xref: /external/skia/src/core/SkImageFilterTypes.cpp

/*
 * Copyright 2019 Google LLC
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "src/core/SkImageFilterTypes.h"

#include "include/core/SkAlphaType.h"
#include "include/core/SkBlendMode.h"
#include "include/core/SkBlender.h"
#include "include/core/SkCanvas.h"
#include "include/core/SkClipOp.h"
#include "include/core/SkColor.h"
#include "include/core/SkColorType.h"
#include "include/core/SkImage.h"
#include "include/core/SkImageInfo.h"
#include "include/core/SkM44.h"
#include "include/core/SkPaint.h"
#include "include/core/SkPicture.h"  // IWYU pragma: keep
#include "include/core/SkShader.h"
#include "include/effects/SkRuntimeEffect.h"
#include "include/private/base/SkDebug.h"
#include "include/private/base/SkFloatingPoint.h"
#include "src/base/SkMathPriv.h"
#include "src/base/SkVx.h"
#include "src/core/SkBitmapDevice.h"
#include "src/core/SkBlenderBase.h"
#include "src/core/SkBlurEngine.h"
#include "src/core/SkCanvasPriv.h"
#include "src/core/SkColorSpacePriv.h"
#include "src/core/SkDevice.h"
#include "src/core/SkImageFilterCache.h"
#include "src/core/SkImageFilter_Base.h"
#include "src/core/SkKnownRuntimeEffects.h"
#include "src/core/SkMatrixPriv.h"
#include "src/core/SkRectPriv.h"
#include "src/core/SkTraceEvent.h"
#include "src/effects/colorfilters/SkColorFilterBase.h"

#include <algorithm>
#include <cmath>
#include <limits>

namespace skif {

namespace {

// This exists to cover up issues where infinite precision would produce integers but float
// math produces values just larger/smaller than an int and roundOut/In on bounds would produce
// nearly a full pixel error. One such case is crbug.com/1313579 where the caller has produced
// near integer CTM and uses integer crop rects that would grab an extra row/column of the
// input image when using a strict roundOut.
static constexpr float kRoundEpsilon = 1e-3f;

std::pair<bool, bool> are_axes_nearly_integer_aligned(const LayerSpace<SkMatrix>& m,
                                                      LayerSpace<SkIPoint>* out=nullptr) {
    float invW  = sk_ieee_float_divide(1.f, m.rc(2,2));
    float tx = SkScalarRoundToScalar(m.rc(0,2)*invW);
    float ty = SkScalarRoundToScalar(m.rc(1,2)*invW);
    // expected = [1 0 tx] after normalizing perspective (divide by m[2,2])
    //            [0 1 ty]
    //            [0 0  1]
    bool affine = SkScalarNearlyEqual(m.rc(2,0)*invW, 0.f, kRoundEpsilon) &&
                  SkScalarNearlyEqual(m.rc(2,1)*invW, 0.f, kRoundEpsilon);
    if (!affine) {
        return {false, false};
    }

    bool xAxis = SkScalarNearlyEqual(1.f, m.rc(0,0)*invW, kRoundEpsilon) &&
                 SkScalarNearlyEqual(0.f, m.rc(0,1)*invW, kRoundEpsilon) &&
                 SkScalarNearlyEqual(tx,  m.rc(0,2)*invW, kRoundEpsilon);
    bool yAxis = SkScalarNearlyEqual(0.f, m.rc(1,0)*invW, kRoundEpsilon) &&
                 SkScalarNearlyEqual(1.f, m.rc(1,1)*invW, kRoundEpsilon) &&
                 SkScalarNearlyEqual(ty,  m.rc(1,2)*invW, kRoundEpsilon);
    if (out && xAxis && yAxis) {
        *out = LayerSpace<SkIPoint>({(int) tx, (int) ty});
    }
    return {xAxis, yAxis};
}

// If m is epsilon within the form [1 0 tx], this returns true and sets out to [tx, ty]
//                                 [0 1 ty]
//                                 [0 0 1 ]
// TODO: Use this in decomposeCTM() (and possibly extend it to support is_nearly_scale_translate)
// to be a little more forgiving on matrix types during layer configuration.
bool is_nearly_integer_translation(const LayerSpace<SkMatrix>& m,
                                   LayerSpace<SkIPoint>* out=nullptr) {
    auto [axisX, axisY] = are_axes_nearly_integer_aligned(m, out);
    return axisX && axisY;
}

void decompose_transform(const SkMatrix& transform, SkPoint representativePoint,
                         SkMatrix* postScaling, SkMatrix* scaling) {
    SkSize scale;
    if (transform.decomposeScale(&scale, postScaling)) {
        *scaling = SkMatrix::Scale(scale.fWidth, scale.fHeight);
    } else {
        // Perspective, which has a non-uniform scaling effect on the filter. Pick a single scale
        // factor that best matches where the filter will be evaluated.
        float approxScale = SkMatrixPriv::DifferentialAreaScale(transform, representativePoint);
        if (SkIsFinite(approxScale) && !SkScalarNearlyZero(approxScale)) {
            // Now take the sqrt to go from an area scale factor to a scaling per X and Y
            approxScale = SkScalarSqrt(approxScale);
        } else {
            // The point was behind the W = 0 plane, so don't factor out any scale.
            approxScale = 1.f;
        }
        if (postScaling) {
            *postScaling = transform;
            float invScale = SkScalarInvert(approxScale);
            postScaling->preScale(invScale, invScale);
        }
        *scaling = SkMatrix::Scale(approxScale, approxScale);
    }
}

std::optional<LayerSpace<SkMatrix>> periodic_axis_transform(
        SkTileMode tileMode,
        const LayerSpace<SkIRect>& crop,
        const LayerSpace<SkIRect>& output) {
    if (tileMode == SkTileMode::kClamp || tileMode == SkTileMode::kDecal) {
        // Not periodic
        return {};
    }

    // Lift crop dimensions into 64 bit so that we can combine with 'output' without worrying about
    // overflowing 32 bits.
    double cropL = (double) crop.left();
    double cropT = (double) crop.top();
    double cropWidth = crop.right() - cropL;
    double cropHeight = crop.bottom() - cropT;

    // Calculate normalized periodic coordinates of 'output' relative to the 'crop' being tiled.
    double periodL = std::floor((output.left() - cropL) / cropWidth);
    double periodT = std::floor((output.top() - cropT) / cropHeight);
    double periodR = std::ceil((output.right() - cropL) / cropWidth);
    double periodB = std::ceil((output.bottom() - cropT) / cropHeight);

    if (periodR - periodL <= 1.0 && periodB - periodT <= 1.0) {
        // The tiling pattern won't be visible, so we can draw the image without tiling and an
        // adjusted transform. We calculate the final translation in double to be exact and then
        // verify that it can round-trip as a float.
        float sx = 1.f;
        float sy = 1.f;
        double tx = -cropL;
        double ty = -cropT;

        if (tileMode == SkTileMode::kMirror) {
            // Flip image when in odd periods on each axis. The periods are stored as doubles but
            // hold integer values since they came from floor or ceil.
            if (std::fmod(periodL, 2.f) > SK_ScalarNearlyZero) {
                sx = -1.f;
                tx = cropWidth - tx;
            }
            if (std::fmod(periodT, 2.f) > SK_ScalarNearlyZero) {
                sy = -1.f;
                ty = cropHeight - ty;
            }
        }
        // Now translate by periods and make relative to crop's top left again. Given 32-bit inputs,
        // the period * dimension shouldn't overflow 64-bits.
        tx += periodL * cropWidth + cropL;
        ty += periodT * cropHeight + cropT;

        // Representing the periodic tiling as a float SkMatrix would lose the pixel precision
        // required to represent it, so don't apply this optimization.
        if (sk_double_saturate2int(tx) != (float) tx ||
            sk_double_saturate2int(ty) != (float) ty) {
            return {};
        }

        SkMatrix periodicTransform;
        periodicTransform.setScaleTranslate(sx, sy, (float) tx, (float) ty);
        return LayerSpace<SkMatrix>(periodicTransform);
    } else {
        // Both low and high edges of the crop would be visible in 'output', or a mirrored
        // boundary is visible in 'output'. Just keep the periodic tiling.
        return {};
    }
}

class RasterBackend : public Backend {
public:

    RasterBackend(const SkSurfaceProps& surfaceProps, SkColorType colorType)
            : Backend(SkImageFilterCache::Get(), surfaceProps, colorType) {}

    sk_sp<SkDevice> makeDevice(SkISize size,
                               sk_sp<SkColorSpace> colorSpace,
                               const SkSurfaceProps* props) const override {
        SkImageInfo imageInfo = SkImageInfo::Make(size,
                                                  this->colorType(),
                                                  kPremul_SkAlphaType,
                                                  std::move(colorSpace));
        return SkBitmapDevice::Create(imageInfo, props ? *props : this->surfaceProps());
    }

    sk_sp<SkSpecialImage> makeImage(const SkIRect& subset, sk_sp<SkImage> image) const override {
        return SkSpecialImages::MakeFromRaster(subset, image, this->surfaceProps());
    }

    sk_sp<SkImage> getCachedBitmap(const SkBitmap& data) const override {
        return SkImages::RasterFromBitmap(data);
    }

#if defined(SK_USE_LEGACY_BLUR_RASTER)
    const SkBlurEngine* getBlurEngine() const override { return nullptr; }
#else
    bool useLegacyFilterResultBlur() const override { return false; }

    const SkBlurEngine* getBlurEngine() const override {
        return SkBlurEngine::GetRasterBlurEngine();
    }
#endif

};

} // anonymous namespace

///////////////////////////////////////////////////////////////////////////////////////////////////

Backend::Backend(sk_sp<SkImageFilterCache> cache,
                 const SkSurfaceProps& surfaceProps,
                 const SkColorType colorType)
        : fCache(std::move(cache))
        , fSurfaceProps(surfaceProps)
        , fColorType(colorType) {}

Backend::~Backend() = default;

sk_sp<Backend> MakeRasterBackend(const SkSurfaceProps& surfaceProps, SkColorType colorType) {
    // TODO (skbug:14286): Remove this forcing to 8888. Many legacy image filters only support
    // N32 on CPU, but once they are implemented in terms of draws and SkSL they will support
    // all color types, like the GPU backends.
    colorType = kN32_SkColorType;

    return sk_make_sp<RasterBackend>(surfaceProps, colorType);
}

void Stats::dumpStats() const {
    SkDebugf("ImageFilter Stats:\n"
             "      # visited filters: %d\n"
             "           # cache hits: %d\n"
             "   # offscreen surfaces: %d\n"
             " # shader-clamped draws: %d\n"
             "   # shader-tiled draws: %d\n",
             fNumVisitedImageFilters,
             fNumCacheHits,
             fNumOffscreenSurfaces,
             fNumShaderClampedDraws,
             fNumShaderBasedTilingDraws);
}

void Stats::reportStats() const {
    TRACE_EVENT_INSTANT2("skia", "ImageFilter Graph Size", TRACE_EVENT_SCOPE_THREAD,
                         "count", fNumVisitedImageFilters, "cache hits", fNumCacheHits);
    TRACE_EVENT_INSTANT1("skia", "ImageFilter Surfaces", TRACE_EVENT_SCOPE_THREAD,
                         "count", fNumOffscreenSurfaces);
    TRACE_EVENT_INSTANT2("skia", "ImageFilter Shader Tiling", TRACE_EVENT_SCOPE_THREAD,
                         "clamp", fNumShaderClampedDraws, "other", fNumShaderBasedTilingDraws);
}

///////////////////////////////////////////////////////////////////////////////////////////////////
// Mapping

SkIRect RoundOut(SkRect r) { return r.makeInset(kRoundEpsilon, kRoundEpsilon).roundOut(); }

SkIRect RoundIn(SkRect r) { return r.makeOutset(kRoundEpsilon, kRoundEpsilon).roundIn(); }

bool Mapping::decomposeCTM(const SkM44& ctm, MatrixCapability capability,
                           const skif::ParameterSpace<SkPoint>& representativePt) {
    SkM44 remainder{SkM44::kUninitialized_Constructor};
    SkM44 layer{SkM44::kUninitialized_Constructor};
    if (capability == MatrixCapability::kTranslate) {
        // Apply the entire CTM post-filtering
        remainder = ctm;
        layer = SkM44();
    } else if (SkMatrixPriv::IsScaleTranslateAsM33(ctm) ||
               capability == MatrixCapability::kComplex) {
        // Either layer space can be anything (kComplex) - or - it can be scale+translate, and the
        // ctm is. In both cases, the layer space can be equivalent to device space.
        remainder = SkM44();
        layer = ctm;
    } else {
        // This case implies some amount of sampling post-filtering, either due to skew or rotation
        // in the original matrix. As such, keep the layer matrix as simple as possible.
        SkMatrix layer33;
        decompose_transform(ctm.asM33(), SkPoint(representativePt),
                            /*postScaling=*/nullptr, &layer33);
        layer = SkM44(layer33);
        // Reconstruct full 4x4 remainder matrix so the mapping doesn't lose the 3rd row/column.
        remainder = ctm;
        remainder.preScale(1.f / layer.rc(0,0), 1.f / layer.rc(1,1));
    }

    SkM44 invRemainder;
    if (!remainder.invert(&invRemainder)) {
        // Under floating point arithmetic, it's possible to decompose an invertible matrix into
        // a scaling matrix and a remainder and have the remainder be non-invertible. Generally
        // when this happens the scale factors are so large and the matrix so ill-conditioned that
        // it's unlikely that any drawing would be reasonable, so failing to make a layer is okay.
        return false;
    } else {
        fParamToLayerMatrix = layer;
        fLayerToDevMatrix = remainder;
        fDevToLayerMatrix = invRemainder;
        return true;
    }
}

bool Mapping::decomposeCTM(const SkM44& ctm,
                           const SkImageFilter* filter,
                           const skif::ParameterSpace<SkPoint>& representativePt) {
    return this->decomposeCTM(
            ctm,
            filter ? as_IFB(filter)->getCTMCapability() : MatrixCapability::kComplex,
            representativePt);
}

bool Mapping::adjustLayerSpace(const SkM44& layer) {
    SkM44 invLayer;
    if (!layer.invert(&invLayer)) {
        return false;
    }
    fParamToLayerMatrix.postConcat(layer);
    fDevToLayerMatrix.postConcat(layer);
    fLayerToDevMatrix.preConcat(invLayer);
    return true;
}

// Instantiate map specializations for the 6 geometric types used during filtering
template<>
SkRect Mapping::map<SkRect>(const SkRect& geom, const SkMatrix& matrix) {
    return geom.isEmpty() ? SkRect::MakeEmpty() : matrix.mapRect(geom);
}

template<>
SkIRect Mapping::map<SkIRect>(const SkIRect& geom, const SkMatrix& matrix) {
    if (geom.isEmpty()) {
        return SkIRect::MakeEmpty();
    }
    // Unfortunately, there is a range of integer values such that we have 1px precision as an int,
    // but less precision as a float. This can lead to non-empty SkIRects becoming empty simply
    // because of float casting. If we're already dealing with a float rect or having a float
    // output, that's what we're stuck with; but if we are starting form an irect and desiring an
    // SkIRect output, we go through efforts to preserve the 1px precision for simple transforms.
    if (matrix.isScaleTranslate()) {
        double l = (double)matrix.getScaleX()*geom.fLeft   + (double)matrix.getTranslateX();
        double r = (double)matrix.getScaleX()*geom.fRight  + (double)matrix.getTranslateX();
        double t = (double)matrix.getScaleY()*geom.fTop    + (double)matrix.getTranslateY();
        double b = (double)matrix.getScaleY()*geom.fBottom + (double)matrix.getTranslateY();
        return {sk_double_saturate2int(std::floor(std::min(l, r) + kRoundEpsilon)),
                sk_double_saturate2int(std::floor(std::min(t, b) + kRoundEpsilon)),
                sk_double_saturate2int(std::ceil(std::max(l, r)  - kRoundEpsilon)),
                sk_double_saturate2int(std::ceil(std::max(t, b)  - kRoundEpsilon))};
    } else {
        return RoundOut(matrix.mapRect(SkRect::Make(geom)));
    }
}

template<>
SkIPoint Mapping::map<SkIPoint>(const SkIPoint& geom, const SkMatrix& matrix) {
    SkPoint p = SkPoint::Make(SkIntToScalar(geom.fX), SkIntToScalar(geom.fY));
    matrix.mapPoints(&p, 1);
    return SkIPoint::Make(SkScalarRoundToInt(p.fX), SkScalarRoundToInt(p.fY));
}

template<>
SkPoint Mapping::map<SkPoint>(const SkPoint& geom, const SkMatrix& matrix) {
    SkPoint p;
    matrix.mapPoints(&p, &geom, 1);
    return p;
}

template<>
Vector Mapping::map<Vector>(const Vector& geom, const SkMatrix& matrix) {
    SkVector v = SkVector::Make(geom.fX, geom.fY);
    matrix.mapVectors(&v, 1);
    return Vector{v};
}

template<>
IVector Mapping::map<IVector>(const IVector& geom, const SkMatrix& matrix) {
    SkVector v = SkVector::Make(SkIntToScalar(geom.fX), SkIntToScalar(geom.fY));
    matrix.mapVectors(&v, 1);
    return IVector(SkScalarRoundToInt(v.fX), SkScalarRoundToInt(v.fY));
}

// Sizes are also treated as non-positioned values (although this assumption breaks down if there's
// perspective). Unlike vectors, we treat input sizes as specifying lengths of the local X and Y
// axes and return the lengths of those mapped axes.
template<>
SkSize Mapping::map<SkSize>(const SkSize& geom, const SkMatrix& matrix) {
    if (matrix.isScaleTranslate()) {
        // This is equivalent to mapping the two basis vectors and calculating their lengths.
        SkVector sizes = matrix.mapVector(geom.fWidth, geom.fHeight);
        return {SkScalarAbs(sizes.fX), SkScalarAbs(sizes.fY)};
    }

    SkVector xAxis = matrix.mapVector(geom.fWidth, 0.f);
    SkVector yAxis = matrix.mapVector(0.f, geom.fHeight);
    return {xAxis.length(), yAxis.length()};
}

template<>
SkISize Mapping::map<SkISize>(const SkISize& geom, const SkMatrix& matrix) {
    SkSize size = map(SkSize::Make(geom), matrix);
    return SkISize::Make(SkScalarCeilToInt(size.fWidth - kRoundEpsilon),
                         SkScalarCeilToInt(size.fHeight - kRoundEpsilon));
}

template<>
SkMatrix Mapping::map<SkMatrix>(const SkMatrix& m, const SkMatrix& matrix) {
    // If 'matrix' maps from the C1 coord space to the C2 coord space, and 'm' is a transform that
    // operates on, and outputs to, the C1 coord space, we want to return a new matrix that is
    // equivalent to 'm' that operates on and outputs to C2. This is the same as mapping the input
    // from C2 to C1 (matrix^-1), then transforming by 'm', and then mapping from C1 to C2 (matrix).
    SkMatrix inv;
    SkAssertResult(matrix.invert(&inv));
    inv.postConcat(m);
    inv.postConcat(matrix);
    return inv;
}

///////////////////////////////////////////////////////////////////////////////////////////////////
// LayerSpace<T>

LayerSpace<SkIRect> LayerSpace<SkIRect>::relevantSubset(const LayerSpace<SkIRect> dstRect,
                                                        SkTileMode tileMode) const {
    LayerSpace<SkIRect> fittedSrc = *this;
    if (tileMode == SkTileMode::kDecal || tileMode == SkTileMode::kClamp) {
        // For both decal/clamp, we only care about the region that is in dstRect, unless we are
        // clamping and have to preserve edge pixels when there's no overlap.
        if (!fittedSrc.intersect(dstRect)) {
            if (tileMode == SkTileMode::kDecal) {
                // The dstRect would be filled with transparent black.
                fittedSrc = LayerSpace<SkIRect>::Empty();
            } else {
                // We just need the closest row/column/corner of this rect to dstRect.
                auto edge = SkRectPriv::ClosestDisjointEdge(SkIRect(fittedSrc),  SkIRect(dstRect));
                fittedSrc = LayerSpace<SkIRect>(edge);
            }
        }
    } // else assume the entire source is needed for periodic tile modes, so leave fittedSrc alone

    return fittedSrc;
}

// Match rounding tolerances of SkRects to SkIRects
LayerSpace<SkISize> LayerSpace<SkSize>::round() const {
    return LayerSpace<SkISize>(fData.toRound());
}
LayerSpace<SkISize> LayerSpace<SkSize>::ceil() const {
    return LayerSpace<SkISize>({SkScalarCeilToInt(fData.fWidth - kRoundEpsilon),
                                SkScalarCeilToInt(fData.fHeight - kRoundEpsilon)});
}
LayerSpace<SkISize> LayerSpace<SkSize>::floor() const {
    return LayerSpace<SkISize>({SkScalarFloorToInt(fData.fWidth + kRoundEpsilon),
                                SkScalarFloorToInt(fData.fHeight + kRoundEpsilon)});
}

LayerSpace<SkRect> LayerSpace<SkMatrix>::mapRect(const LayerSpace<SkRect>& r) const {
    return LayerSpace<SkRect>(Mapping::map(SkRect(r), fData));
}

// Effectively mapRect(SkRect).roundOut() but more accurate when the underlying matrix or
// SkIRect has large floating point values.
LayerSpace<SkIRect> LayerSpace<SkMatrix>::mapRect(const LayerSpace<SkIRect>& r) const {
    return LayerSpace<SkIRect>(Mapping::map(SkIRect(r), fData));
}

LayerSpace<SkPoint> LayerSpace<SkMatrix>::mapPoint(const LayerSpace<SkPoint>& p) const {
    return LayerSpace<SkPoint>(Mapping::map(SkPoint(p), fData));
}

LayerSpace<Vector> LayerSpace<SkMatrix>::mapVector(const LayerSpace<Vector>& v) const {
    return LayerSpace<Vector>(Mapping::map(Vector(v), fData));
}

LayerSpace<SkSize> LayerSpace<SkMatrix>::mapSize(const LayerSpace<SkSize>& s) const {
    return LayerSpace<SkSize>(Mapping::map(SkSize(s), fData));
}

bool LayerSpace<SkMatrix>::inverseMapRect(const LayerSpace<SkRect>& r,
                                          LayerSpace<SkRect>* out) const {
    SkRect mapped;
    if (r.isEmpty()) {
        // An empty input always inverse maps to an empty rect "successfully"
        *out = LayerSpace<SkRect>::Empty();
        return true;
    } else if (SkMatrixPriv::InverseMapRect(fData, &mapped, SkRect(r))) {
        *out = LayerSpace<SkRect>(mapped);
        return true;
    } else {
        return false;
    }
}

bool LayerSpace<SkMatrix>::inverseMapRect(const LayerSpace<SkIRect>& rect,
                                          LayerSpace<SkIRect>* out) const {
    if (rect.isEmpty()) {
        // An empty input always inverse maps to an empty rect "successfully"
        *out = LayerSpace<SkIRect>::Empty();
        return true;
    } else if (fData.isScaleTranslate()) { // Specialized inverse of 1px-preserving map<SkIRect>
        // A scale-translate matrix with a 0 scale factor is not invertible.
        if (fData.getScaleX() == 0.f || fData.getScaleY() == 0.f) {
            return false;
        }
        double l = (rect.left()   - (double)fData.getTranslateX()) / (double)fData.getScaleX();
        double r = (rect.right()  - (double)fData.getTranslateX()) / (double)fData.getScaleX();
        double t = (rect.top()    - (double)fData.getTranslateY()) / (double)fData.getScaleY();
        double b = (rect.bottom() - (double)fData.getTranslateY()) / (double)fData.getScaleY();

        SkIRect mapped{sk_double_saturate2int(std::floor(std::min(l, r) + kRoundEpsilon)),
                       sk_double_saturate2int(std::floor(std::min(t, b) + kRoundEpsilon)),
                       sk_double_saturate2int(std::ceil(std::max(l, r)  - kRoundEpsilon)),
                       sk_double_saturate2int(std::ceil(std::max(t, b)  - kRoundEpsilon))};
        *out = LayerSpace<SkIRect>(mapped);
        return true;
    } else {
        SkRect mapped;
        if (SkMatrixPriv::InverseMapRect(fData, &mapped, SkRect::Make(SkIRect(rect)))) {
            *out = LayerSpace<SkRect>(mapped).roundOut();
            return true;
        }
    }

    return false;
}

///////////////////////////////////////////////////////////////////////////////////////////////////
// FilterResult::AutoSurface
//
// AutoSurface manages an SkCanvas and device state to draw to a layer-space bounding box,
// and then snap it into a FilterResult. It provides operators to be used directly as an SkDevice,
// assuming surface creation succeeded. It can also be viewed as an SkCanvas (for when an operation
// is unavailable on SkDevice). A given AutoSurface should only rely on one access API.
// Usage:
//
//     AutoSurface surface{ctx, dstBounds, renderInParameterSpace}; // if true, concats layer matrix
//     if (surface) {
//         surface->drawFoo(...);
//     }
//     return surface.snap(); // Automatically handles failed allocations
class FilterResult::AutoSurface {
public:
    AutoSurface(const Context& ctx,
                const LayerSpace<SkIRect>& dstBounds,
                PixelBoundary boundary,
                bool renderInParameterSpace,
                const SkSurfaceProps* props = nullptr)
            : fDstBounds(dstBounds)
            , fBoundary(boundary) {
        // We don't intersect by ctx.desiredOutput() and only use the Context to make the surface.
        // It is assumed the caller has already accounted for the desired output, or it's a
        // situation where the desired output shouldn't apply (e.g. this surface will be transformed
        // to align with the actual desired output via FilterResult metadata).
        sk_sp<SkDevice> device = nullptr;
        if (!dstBounds.isEmpty()) {
            int padding = this->padding();
            if (padding) {
                fDstBounds.outset(LayerSpace<SkISize>({padding, padding}));
                // If we are dealing with pathological inputs, the bounds may be near the maximum
                // represented by an int, in which case the outset gets saturated and we don't end
                // up with the expected padding pixels. We could downgrade the boundary value in
                // this case, but given that these values are going to be causing problems for any
                // of the floating point math during rendering we just fail.
                if (fDstBounds.left() >= dstBounds.left() ||
                    fDstBounds.right() <= dstBounds.right() ||
                    fDstBounds.top() >= dstBounds.top() ||
                    fDstBounds.bottom() <= dstBounds.bottom()) {
                    return;
                }
            }
            device = ctx.backend()->makeDevice(SkISize(fDstBounds.size()),
                                               ctx.refColorSpace(),
                                               props);
        }

        if (!device) {
            return;
        }

        // Wrap the device in a canvas and use that to configure its origin and clip. This ensures
        // the device and the canvas are in sync regardless of how the AutoSurface user intends
        // to render.
        ctx.markNewSurface();
        fCanvas.emplace(std::move(device));
        fCanvas->translate(-fDstBounds.left(), -fDstBounds.top());
        fCanvas->clear(SkColors::kTransparent);
        if (fBoundary == PixelBoundary::kTransparent) {
            // Clip to the original un-padded dst bounds, ensuring that the border pixels remain
            // fully transparent.
            fCanvas->clipIRect(SkIRect(dstBounds));
        } else {
            // Otherwise clip to the possibly padded fDstBounds, if the backend made an approx-fit
            // surface. If the bounds were padded for PixelBoundary::kInitialized, this will allow
            // the border pixels to be rendered naturally.
            fCanvas->clipIRect(SkIRect(fDstBounds));
        }

        if (renderInParameterSpace) {
            fCanvas->concat(ctx.mapping().layerMatrix());
        }
    }

    explicit operator bool() const { return fCanvas.has_value(); }

    SkCanvas* canvas() { SkASSERT(fCanvas.has_value()); return &*fCanvas; }
    SkDevice* device() { return SkCanvasPriv::TopDevice(this->canvas()); }
    SkCanvas* operator->() { return this->canvas(); }

    FilterResult snap() {
        if (fCanvas.has_value()) {
            // Finish everything and mark the device as immutable so that snapSpecial() can avoid
            // copying data.
            fCanvas->restoreToCount(0);
            this->device()->setImmutable();

            // Snap a subset of the device with the padded dst bounds
            SkIRect subset = SkIRect::MakeWH(fDstBounds.width(), fDstBounds.height());
            sk_sp<SkSpecialImage> image = this->device()->snapSpecial(subset);
            fCanvas.reset(); // Only use the AutoSurface once

            if (image && fBoundary != PixelBoundary::kUnknown) {
                // Inset subset relative to 'image' reported size
                const int padding = this->padding();
                subset = SkIRect::MakeSize(image->dimensions()).makeInset(padding, padding);
                LayerSpace<SkIPoint> origin{{fDstBounds.left() + padding,
                                             fDstBounds.top() + padding}};
                return {image->makeSubset(subset), origin, fBoundary};
            } else {
                // No adjustment to make
                return {image, fDstBounds.topLeft(), PixelBoundary::kUnknown};
            }
        } else {
            return {};
        }
    }

private:
    int padding() const { return fBoundary == PixelBoundary::kUnknown ? 0 : 1; }

    std::optional<SkCanvas> fCanvas;
    LayerSpace<SkIRect> fDstBounds; // includes padding, if any
    PixelBoundary fBoundary;
};

///////////////////////////////////////////////////////////////////////////////////////////////////
// FilterResult

sk_sp<SkSpecialImage> FilterResult::imageAndOffset(const Context& ctx, SkIPoint* offset) const {
    auto [image, origin] = this->imageAndOffset(ctx);
    *offset = SkIPoint(origin);
    return image;
}

std::pair<sk_sp<SkSpecialImage>, LayerSpace<SkIPoint>>FilterResult::imageAndOffset(
        const Context& ctx) const {
    FilterResult resolved = this->resolve(ctx, ctx.desiredOutput());
    return {resolved.fImage, resolved.layerBounds().topLeft()};
}

FilterResult FilterResult::insetForSaveLayer() const {
    if (!fImage) {
        return {};
    }

    // SkCanvas processing should have prepared a decal-tiled image before calling this.
    SkASSERT(fTileMode == SkTileMode::kDecal);

    // PixelBoundary tracking assumes the special image's subset does not include the padding, so
    // inset by a single pixel.
    FilterResult inset = this->insetByPixel();
    // Trust that SkCanvas configured the layer's SkDevice to ensure the padding remained
    // transparent. Upgrading this pixel boundary knowledge allows the source image to use the
    // simpler clamp math (vs. decal math) when used in a shader context.
    SkASSERT(inset.fBoundary == PixelBoundary::kInitialized &&
             inset.fTileMode == SkTileMode::kDecal);
    inset.fBoundary = PixelBoundary::kTransparent;
    return inset;
}

FilterResult FilterResult::insetByPixel() const {
    // This assumes that the image is pixel aligned with its layer bounds, which is validated in
    // the call to subset().
    auto insetBounds = fLayerBounds;
    insetBounds.inset(LayerSpace<SkISize>({1, 1}));
     // Shouldn't be calling this except in situations where padding was explicitly added before.
    SkASSERT(!insetBounds.isEmpty());
    return this->subset(fLayerBounds.topLeft(), insetBounds);
}

SkEnumBitMask<FilterResult::BoundsAnalysis> FilterResult::analyzeBounds(
        const SkMatrix& xtraTransform,
        const SkIRect& dstBounds,
        BoundsScope scope) const {
    static constexpr SkSamplingOptions kNearestNeighbor = {};
    static constexpr float kHalfPixel = 0.5f;
    static constexpr float kCubicRadius = 1.5f;

    SkEnumBitMask<BoundsAnalysis> analysis = BoundsAnalysis::kSimple;
    const bool fillsLayerBounds = fTileMode != SkTileMode::kDecal ||
                                  (fColorFilter && as_CFB(fColorFilter)->affectsTransparentBlack());

    // 1. Is the layer geometry visible in the dstBounds (ignoring whether or not there are shading
    //    effects that highlight that boundary).
    SkRect pixelCenterBounds = SkRect::Make(dstBounds);
    if (!SkRectPriv::QuadContainsRect(xtraTransform,
                                      SkIRect(fLayerBounds),
                                      dstBounds,
                                      kRoundEpsilon)) {
        // 1a. If an effect doesn't fill out to the layer bounds, is the image content itself
        //     clipped by the layer bounds?
        bool requireLayerCrop = fillsLayerBounds;
        if (!fillsLayerBounds) {
            LayerSpace<SkIRect> imageBounds =
                    fTransform.mapRect(LayerSpace<SkIRect>{fImage->dimensions()});
            requireLayerCrop = !fLayerBounds.contains(imageBounds);
        }

        if (requireLayerCrop) {
            analysis |= BoundsAnalysis::kRequiresLayerCrop;
            // And since the layer crop will have to be applied externally, we can restrict the
            // sample bounds to the intersection of dstBounds and layerBounds
            SkIRect layerBoundsInDst = Mapping::map(SkIRect(fLayerBounds), xtraTransform);
            // In some cases these won't intersect, usually in a complex graph where the input is
            // a bitmap or the dynamic source, in which case it hasn't been clipped or dropped by
            // earlier image filter processing for that particular node. We could return a flag here
            // to signal that the operation should be treated as transparent black, but that would
            // create more shader combinations and image sampling will still do the right thing by
            // leaving 'pixelCenterBounds' as the original 'dstBounds'.
            (void) pixelCenterBounds.intersect(SkRect::Make(layerBoundsInDst));
        }
        // else this is a decal-tiled, non-transparent affecting FilterResult that doesn't have
        // its pixel data clipped by the layer bounds, so the layer crop doesn't have to be applied
        // separately. But this means that the image will be sampled over all of 'dstBounds'.
    }
    // else the layer bounds geometry isn't visible, so 'dstBounds' is already a tighter bounding
    // box for how the image will be sampled.

    // 2. Are the tiling and deferred color filter effects visible in the sampled bounds
    SkRect imageBounds = SkRect::Make(fImage->dimensions());
    LayerSpace<SkMatrix> netTransform = fTransform;
    netTransform.postConcat(LayerSpace<SkMatrix>(xtraTransform));
    SkM44 netM44{SkMatrix(netTransform)};

    const auto [xAxisAligned, yAxisAligned] = are_axes_nearly_integer_aligned(netTransform);
    const bool isPixelAligned = xAxisAligned && yAxisAligned;
    // When decal sampling, we use an inset image bounds for checking if the dst is covered. If not,
    // an image that exactly filled the dst bounds could still sample transparent black, in which
    // case the transform's scale factor needs to be taken into account.
    const bool decalLeaks = scope != BoundsScope::kRescale &&
                            fTileMode == SkTileMode::kDecal &&
                            fSamplingOptions != kNearestNeighbor &&
                            !isPixelAligned;

    const float sampleRadius = fSamplingOptions.useCubic ? kCubicRadius : kHalfPixel;
    SkRect safeImageBounds = imageBounds.makeInset(sampleRadius, sampleRadius);
    if (fSamplingOptions == kDefaultSampling && !isPixelAligned) {
        // When using default sampling, integer translations are eventually downgraded to nearest
        // neighbor, so the 1/2px inset clamping is sufficient to safely access within the subset.
        // When staying with linear filtering, a sample at 1/2px inset exactly will end up accessing
        // one external pixel with a weight of 0 (but MSAN will complain and not all GPUs actually
        // seem to get that correct). To be safe we have to clamp to epsilon inside the 1/2px.
        safeImageBounds.inset(xAxisAligned ? 0.f : kRoundEpsilon,
                              yAxisAligned ? 0.f : kRoundEpsilon);
    }
    bool hasPixelPadding = fBoundary != PixelBoundary::kUnknown;

    if (!SkRectPriv::QuadContainsRect(netM44,
                                      decalLeaks ? safeImageBounds : imageBounds,
                                      pixelCenterBounds,
                                      kRoundEpsilon)) {
        analysis |= BoundsAnalysis::kDstBoundsNotCovered;
        if (fillsLayerBounds) {
            analysis |= BoundsAnalysis::kHasLayerFillingEffect;
        }
        if (decalLeaks) {
            // Some amount of decal tiling will be visible in the output so check the relative size
            // of the decal interpolation from texel to dst space; if it's not close to 1 it needs
            // to be handled specially to keep rendering methods visually consistent.
            float scaleFactors[2];
            if (!(SkMatrix(netTransform).getMinMaxScales(scaleFactors) &&
                    SkScalarNearlyEqual(scaleFactors[0], 1.f, 0.2f) &&
                    SkScalarNearlyEqual(scaleFactors[1], 1.f, 0.2f))) {
                analysis |= BoundsAnalysis::kRequiresDecalInLayerSpace;
                if (fBoundary == PixelBoundary::kTransparent) {
                    // Turn off considering the transparent padding as safe to prevent that
                    // transparency from multiplying with the layer-space decal effect.
                    hasPixelPadding = false;
                }
            }
        }
    }

    if (scope == BoundsScope::kDeferred) {
        return analysis; // skip sampling analysis
    } else if (scope == BoundsScope::kCanDrawDirectly &&
               !(analysis & BoundsAnalysis::kHasLayerFillingEffect)) {
        // When drawing the image directly, the geometry is limited to the image. If the texels
        // are pixel aligned, then it is safe to skip shader-based tiling.
        const bool nnOrBilerp = fSamplingOptions == kDefaultSampling ||
                                fSamplingOptions == kNearestNeighbor;
        if (nnOrBilerp && (hasPixelPadding || isPixelAligned)) {
            return analysis;
        }
    }

    // 3. Would image pixels outside of its subset be sampled if shader-clamping is skipped?

    // Include the padding for sampling analysis and inset the dst by 1/2 px to represent where the
    // sampling is evaluated at.
    if (hasPixelPadding) {
        safeImageBounds.outset(1.f, 1.f);
    }
    pixelCenterBounds.inset(kHalfPixel, kHalfPixel);

    // True if all corners of 'pixelCenterBounds' are on the inside of each edge of
    // 'safeImageBounds', ordered T,R,B,L.
    skvx::int4 edgeMask = SkRectPriv::QuadContainsRectMask(netM44,
                                                           safeImageBounds,
                                                           pixelCenterBounds,
                                                           kRoundEpsilon);
    if (!all(edgeMask)) {
        // Sampling outside the image subset occurs, but if the edges that are exceeded are HW
        // edges, then we can avoid using shader-based tiling.
        skvx::int4 hwEdge{fImage->subset().fTop == 0,
                          fImage->subset().fRight == fImage->backingStoreDimensions().fWidth,
                          fImage->subset().fBottom == fImage->backingStoreDimensions().fHeight,
                          fImage->subset().fLeft == 0};
        if (fTileMode == SkTileMode::kRepeat || fTileMode == SkTileMode::kMirror) {
            // For periodic tile modes, we require both edges on an axis to be HW edges
            hwEdge = hwEdge & skvx::shuffle<2,3,0,1>(hwEdge); // TRBL & BLTR
        }
        if (!all(edgeMask | hwEdge)) {
            analysis |= BoundsAnalysis::kRequiresShaderTiling;
        }
    }

    return analysis;
}

void FilterResult::updateTileMode(const Context& ctx, SkTileMode tileMode) {
    if (fImage) {
        fTileMode = tileMode;
        if (tileMode != SkTileMode::kDecal) {
            fLayerBounds = ctx.desiredOutput();
        }
    }
}

FilterResult FilterResult::applyCrop(const Context& ctx,
                                     const LayerSpace<SkIRect>& crop,
                                     SkTileMode tileMode) const {
    static const LayerSpace<SkMatrix> kIdentity{SkMatrix::I()};

    if (crop.isEmpty() || ctx.desiredOutput().isEmpty()) {
        // An empty crop cannot be anything other than fully transparent
        return {};
    }

    // First, determine how this image's layer bounds interact with the crop rect, which determines
    // the portion of 'crop' that could have non-transparent content.
    LayerSpace<SkIRect> cropContent = crop;
    if (!fImage ||
        !cropContent.intersect(fLayerBounds)) {
        // The pixels within 'crop' would be fully transparent, and tiling won't change that.
        return {};
    }

    // Second, determine the subset of 'crop' that is relevant to ctx.desiredOutput().
    LayerSpace<SkIRect> fittedCrop = crop.relevantSubset(ctx.desiredOutput(), tileMode);

    // Third, check if there's overlap with the known non-transparent cropped content and what's
    // used to tile the desired output. If not, the image is known to be empty. This modifies
    // 'cropContent' and not 'fittedCrop' so that any transparent padding remains if we have to
    // apply repeat/mirror tiling to the original geometry.
    if (!cropContent.intersect(fittedCrop)) {
        return {};
    }

    // Fourth, a periodic tiling that covers the output with a single instance of the image can be
    // simplified to just a transform.
    auto periodicTransform = periodic_axis_transform(tileMode, fittedCrop, ctx.desiredOutput());
    if (periodicTransform) {
        return this->applyTransform(ctx, *periodicTransform, FilterResult::kDefaultSampling);
    }

    bool preserveTransparencyInCrop = false;
    if (tileMode == SkTileMode::kDecal) {
        // We can reduce the crop dimensions to what's non-transparent
        fittedCrop = cropContent;
    } else if (fittedCrop.contains(ctx.desiredOutput())) {
        tileMode = SkTileMode::kDecal;
        fittedCrop = ctx.desiredOutput();
    } else if (!cropContent.contains(fittedCrop)) {
        // There is transparency in fittedCrop that must be resolved in order to maintain the new
        // tiling geometry.
        preserveTransparencyInCrop = true;
        if (fTileMode == SkTileMode::kDecal && tileMode == SkTileMode::kClamp) {
            // include 1px buffer for transparency from original kDecal tiling
            cropContent.outset(skif::LayerSpace<SkISize>({1, 1}));
            SkAssertResult(fittedCrop.intersect(cropContent));
        }
    } // Otherwise cropContent == fittedCrop

    // Fifth, when the transform is an integer translation, any prior tiling and the new tiling
    // can sometimes be addressed analytically without producing a new image. Moving the crop into
    // the image dimensions allows future operations like applying a transform or color filter to
    // be composed without rendering a new image since there will not be an intervening crop.
    const bool doubleClamp = fTileMode == SkTileMode::kClamp && tileMode == SkTileMode::kClamp;
    LayerSpace<SkIPoint> origin;
    if (!preserveTransparencyInCrop &&
        is_nearly_integer_translation(fTransform, &origin) &&
        (doubleClamp ||
         !(this->analyzeBounds(fittedCrop) & BoundsAnalysis::kHasLayerFillingEffect))) {
        // Since the transform is axis-aligned, the tile mode can be applied to the original
        // image pre-transformation and still be consistent with the 'crop' geometry. When the
        // original tile mode is decal, extract_subset is always valid. When the original mode is
        // mirror/repeat, !kHasLayerFillingEffect ensures that 'fittedCrop' is contained within
        // the base image bounds, so extract_subset is valid. When the original mode is clamp
        // and the new mode is not clamp, that is also the case. When both modes are clamp, we have
        // to consider how 'fittedCrop' intersects (or doesn't) with the base image bounds.
        FilterResult restrictedOutput = this->subset(origin, fittedCrop, doubleClamp);
        restrictedOutput.updateTileMode(ctx, tileMode);
        if (restrictedOutput.fBoundary == PixelBoundary::kInitialized ||
            tileMode != SkTileMode::kDecal) {
            // Discard kInitialized since a crop is a strict constraint on sampling outside of it.
            // But preserve (kTransparent+kDecal) if this is a no-op crop.
            restrictedOutput.fBoundary = PixelBoundary::kUnknown;
        }
        return restrictedOutput;
    } else if (tileMode == SkTileMode::kDecal) {
        // A decal crop can always be applied as the final operation by adjusting layer bounds, and
        // does not modify any prior tile mode.
        SkASSERT(!preserveTransparencyInCrop);
        FilterResult restrictedOutput = *this;
        restrictedOutput.fLayerBounds = fittedCrop;
        return restrictedOutput;
    } else {
        // There is a non-trivial transform to the image data that must be applied before the
        // non-decal tilemode is meant to be applied to the axis-aligned 'crop'.
        FilterResult tiled = this->resolve(ctx, fittedCrop, /*preserveDstBounds=*/true);
        tiled.updateTileMode(ctx, tileMode);
        return tiled;
    }
}

FilterResult FilterResult::applyColorFilter(const Context& ctx,
                                            sk_sp<SkColorFilter> colorFilter) const {
    // A null filter is the identity, so it should have been caught during image filter DAG creation
    SkASSERT(colorFilter);

    if (ctx.desiredOutput().isEmpty()) {
        return {};
    }

    // Color filters are applied after the transform and image sampling, but before the fLayerBounds
    // crop. We can compose 'colorFilter' with any previously applied color filter regardless
    // of the transform/sample state, so long as it respects the effect of the current crop.
    LayerSpace<SkIRect> newLayerBounds = fLayerBounds;
    if (as_CFB(colorFilter)->affectsTransparentBlack()) {
        if (!fImage || !newLayerBounds.intersect(ctx.desiredOutput())) {
            // The current image's intersection with the desired output is fully transparent, but
            // the new color filter converts that into a non-transparent color. The desired output
            // is filled with this color, but use a 1x1 surface and clamp tiling.
            AutoSurface surface{ctx,
                                LayerSpace<SkIRect>{SkIRect::MakeXYWH(ctx.desiredOutput().left(),
                                                                      ctx.desiredOutput().top(),
                                                                      1, 1)},
                                PixelBoundary::kInitialized,
                                /*renderInParameterSpace=*/false};
            if (surface) {
                SkPaint paint;
                paint.setColor4f(SkColors::kTransparent, /*colorSpace=*/nullptr);
                paint.setColorFilter(std::move(colorFilter));
#if !defined(SK_USE_SRCOVER_FOR_FILTERS)
                paint.setBlendMode(SkBlendMode::kSrc);
#endif
                surface->drawPaint(paint);
            }
            FilterResult solidColor = surface.snap();
            solidColor.updateTileMode(ctx, SkTileMode::kClamp);
            return solidColor;
        }

        if (this->analyzeBounds(ctx.desiredOutput()) & BoundsAnalysis::kRequiresLayerCrop) {
            // Since 'colorFilter' modifies transparent black, the new result's layer bounds must
            // be the desired output. But if the current image is cropped we need to resolve the
            // image to avoid losing the effect of the current 'fLayerBounds'.
            newLayerBounds.outset(LayerSpace<SkISize>({1, 1}));
            SkAssertResult(newLayerBounds.intersect(ctx.desiredOutput()));
            FilterResult filtered = this->resolve(ctx, newLayerBounds, /*preserveDstBounds=*/true);
            filtered.fColorFilter = std::move(colorFilter);
            filtered.updateTileMode(ctx, SkTileMode::kClamp);
            return filtered;
        }

        // otherwise we can fill out to the desired output without worrying about losing the crop.
        newLayerBounds = ctx.desiredOutput();
    } else {
        if (!fImage || !LayerSpace<SkIRect>::Intersects(newLayerBounds, ctx.desiredOutput())) {
            // The color filter does not modify transparent black, so it remains transparent
            return {};
        }
        // otherwise a non-transparent affecting color filter can always be lifted before any crop
        // because it does not change the "shape" of the prior FilterResult.
    }

    // If we got here we can compose the new color filter with the previous filter and the prior
    // layer bounds are either soft-cropped to the desired output, or we fill out the desired output
    // when the new color filter affects transparent black. We don't check if the entire composed
    // filter affects transparent black because earlier floods are restricted by the layer bounds.
    FilterResult filtered = *this;
    filtered.fLayerBounds = newLayerBounds;
    filtered.fColorFilter = SkColorFilters::Compose(std::move(colorFilter), fColorFilter);
    return filtered;
}

static bool compatible_sampling(const SkSamplingOptions& currentSampling,
                                bool currentXformWontAffectNearest,
                                SkSamplingOptions* nextSampling,
                                bool nextXformWontAffectNearest) {
    // Both transforms could perform non-trivial sampling, but if they are similar enough we
    // assume performing one non-trivial sampling operation with the concatenated transform will
    // not be visually distinguishable from sampling twice.
    // TODO(michaelludwig): For now ignore mipmap policy, SkSpecialImages are not supposed to be
    // drawn with mipmapping, and the majority of filter steps produce images that are at the
    // proper scale and do not define mip levels. The main exception is the ::Image() filter
    // leaf but that doesn't use this system yet.
    if (currentSampling.isAniso() && nextSampling->isAniso()) {
        // Assume we can get away with one sampling at the highest anisotropy level
        *nextSampling =  SkSamplingOptions::Aniso(std::max(currentSampling.maxAniso,
                                                           nextSampling->maxAniso));
        return true;
    } else if (currentSampling.isAniso() && nextSampling->filter == SkFilterMode::kLinear) {
        // Assume we can get away with the current anisotropic filter since the next is linear
        *nextSampling = currentSampling;
        return true;
    } else if (nextSampling->isAniso() && currentSampling.filter == SkFilterMode::kLinear) {
        // Mirror of the above, assume we can just get away with next's anisotropic filter
        return true;
    } else if (currentSampling.useCubic && (nextSampling->filter == SkFilterMode::kLinear ||
                                            (nextSampling->useCubic &&
                                             currentSampling.cubic.B == nextSampling->cubic.B &&
                                             currentSampling.cubic.C == nextSampling->cubic.C))) {
        // Assume we can get away with the current bicubic filter, since the next is the same
        // or a bilerp that can be upgraded.
        *nextSampling = currentSampling;
        return true;
    } else if (nextSampling->useCubic && currentSampling.filter == SkFilterMode::kLinear) {
        // Mirror of the above, assume we can just get away with next's cubic resampler
        return true;
    } else if (currentSampling.filter == SkFilterMode::kLinear &&
               nextSampling->filter == SkFilterMode::kLinear) {
        // Assume we can get away with a single bilerp vs. the two
        return true;
    } else if (nextSampling->filter == SkFilterMode::kNearest && currentXformWontAffectNearest) {
        // The next transform and nearest-neighbor filtering isn't impacted by the current transform
        SkASSERT(currentSampling.filter == SkFilterMode::kLinear);
        return true;
    } else if (currentSampling.filter == SkFilterMode::kNearest && nextXformWontAffectNearest) {
        // The next transform doesn't change the nearest-neighbor filtering of the current transform
        SkASSERT(nextSampling->filter == SkFilterMode::kLinear);
        *nextSampling = currentSampling;
        return true;
    } else {
        // The current or next sampling is nearest neighbor, and will produce visible texels
        // oriented with the current transform; assume this is a desired effect and preserve it.
        return false;
    }
}

FilterResult FilterResult::applyTransform(const Context& ctx,
                                          const LayerSpace<SkMatrix>& transform,
                                          const SkSamplingOptions &sampling) const {
    if (!fImage || ctx.desiredOutput().isEmpty()) {
        // Transformed transparent black remains transparent black.
        SkASSERT(!fColorFilter);
        return {};
    }

    if (!transform.invert(nullptr)) {
        return {};
    }

    // Extract the sampling options that matter based on the current and next transforms.
    // We make sure the new sampling is bilerp (default) if the new transform doesn't matter
    // (and assert that the current is bilerp if its transform didn't matter). Bilerp can be
    // maximally combined, so simplifies the logic in compatible_sampling().
    const bool currentXformIsInteger = is_nearly_integer_translation(fTransform);
    const bool nextXformIsInteger = is_nearly_integer_translation(transform);

    SkASSERT(!currentXformIsInteger || fSamplingOptions == kDefaultSampling);
    SkSamplingOptions nextSampling = nextXformIsInteger ? kDefaultSampling : sampling;

    // Determine if the image is being visibly cropped by the layer bounds, in which case we can't
    // merge this transform with any previous transform (unless the new transform is an integer
    // translation in which case any visible edge is aligned with the desired output and can be
    // resolved by intersecting the transformed layer bounds and the output bounds).
    bool isCropped = !nextXformIsInteger &&
                     (this->analyzeBounds(SkMatrix(transform), SkIRect(ctx.desiredOutput()))
                            & BoundsAnalysis::kRequiresLayerCrop);

    FilterResult transformed;
    if (!isCropped && compatible_sampling(fSamplingOptions, currentXformIsInteger,
                                          &nextSampling, nextXformIsInteger)) {
        // We can concat transforms and 'nextSampling' will be either fSamplingOptions,
        // sampling, or a merged combination depending on the two transforms in play.
        transformed = *this;
    } else {
        // We'll have to resolve this FilterResult first before 'transform' and 'sampling' can be
        // correctly evaluated. 'nextSampling' will always be 'sampling'.
        LayerSpace<SkIRect> tightBounds;
        if (transform.inverseMapRect(ctx.desiredOutput(), &tightBounds)) {
            transformed = this->resolve(ctx, tightBounds);
        }

        if (!transformed.fImage) {
            // Transform not invertible or resolve failed to create an image
            return {};
        }
    }

    transformed.fSamplingOptions = nextSampling;
    transformed.fTransform.postConcat(transform);
    // Rebuild the layer bounds and then restrict to the current desired output. The original value
    // of fLayerBounds includes the image mapped by the original fTransform as well as any
    // accumulated soft crops from desired outputs of prior stages. To prevent discarding that info,
    // we map fLayerBounds by the additional transform, instead of re-mapping the image bounds.
    transformed.fLayerBounds = transform.mapRect(transformed.fLayerBounds);
    if (!LayerSpace<SkIRect>::Intersects(transformed.fLayerBounds, ctx.desiredOutput())) {
        // The transformed output doesn't touch the desired, so it would just be transparent black.
        return {};
    }

    return transformed;
}

FilterResult FilterResult::resolve(const Context& ctx,
                                   LayerSpace<SkIRect> dstBounds,
                                   bool preserveDstBounds) const {
    // The layer bounds is the final clip, so it can always be used to restrict 'dstBounds'. Even
    // if there's a non-decal tile mode or transparent-black affecting color filter, those floods
    // are restricted to fLayerBounds.
    if (!fImage || (!preserveDstBounds && !dstBounds.intersect(fLayerBounds))) {
        return {nullptr, {}};
    }

    // If we have any extra effect to apply, there's no point in trying to extract a subset.
    const bool subsetCompatible = !fColorFilter &&
                                  fTileMode == SkTileMode::kDecal &&
                                  !preserveDstBounds;

    // TODO(michaelludwig): If we get to the point where all filter results track bounds in
    // floating point, then we can extend this case to any S+T transform.
    LayerSpace<SkIPoint> origin;
    if (subsetCompatible && is_nearly_integer_translation(fTransform, &origin)) {
        return this->subset(origin, dstBounds);
    } // else fall through and attempt a draw

    // Don't use context properties to avoid DMSAA on internal stages of filter evaluation.
    SkSurfaceProps props = {};
    PixelBoundary boundary = preserveDstBounds ? PixelBoundary::kUnknown
                                               : PixelBoundary::kTransparent;
    AutoSurface surface{ctx, dstBounds, boundary, /*renderInParameterSpace=*/false, &props};
    if (surface) {
        this->draw(ctx, surface.device(), /*preserveDeviceState=*/false);
    }
    return surface.snap();
}

FilterResult FilterResult::subset(const LayerSpace<SkIPoint>& knownOrigin,
                                  const LayerSpace<SkIRect>& subsetBounds,
                                  bool clampSrcIfDisjoint) const {
    SkDEBUGCODE(LayerSpace<SkIPoint> actualOrigin;)
    SkASSERT(is_nearly_integer_translation(fTransform, &actualOrigin) &&
             SkIPoint(actualOrigin) == SkIPoint(knownOrigin));


    LayerSpace<SkIRect> imageBounds(SkIRect::MakeXYWH(knownOrigin.x(), knownOrigin.y(),
                                                      fImage->width(), fImage->height()));
    imageBounds = imageBounds.relevantSubset(subsetBounds, clampSrcIfDisjoint ? SkTileMode::kClamp
                                                                              : SkTileMode::kDecal);
    if (imageBounds.isEmpty()) {
        return {};
    }

    // Offset the image subset directly to avoid issues negating (origin). With the prior
    // intersection (bounds - origin) will be >= 0, but (bounds + (-origin)) may not, (e.g.
    // origin is INT_MIN).
    SkIRect subset = { imageBounds.left() - knownOrigin.x(),
                       imageBounds.top() - knownOrigin.y(),
                       imageBounds.right() - knownOrigin.x(),
                       imageBounds.bottom() - knownOrigin.y() };
    SkASSERT(subset.fLeft >= 0 && subset.fTop >= 0 &&
             subset.fRight <= fImage->width() && subset.fBottom <= fImage->height());

    FilterResult result{fImage->makeSubset(subset), imageBounds.topLeft()};
    result.fColorFilter = fColorFilter;

    // Update what's known about PixelBoundary based on how the subset aligns.
    SkASSERT(result.fBoundary == PixelBoundary::kUnknown);
    // If the pixel bounds didn't change, preserve the original boundary value
    if (fImage->subset() == result.fImage->subset()) {
        result.fBoundary = fBoundary;
    } else {
        // If the new pixel bounds are bordered by valid data, upgrade to kInitialized
        SkIRect safeSubset = fImage->subset();
        if (fBoundary == PixelBoundary::kUnknown) {
            safeSubset.inset(1, 1);
        }
        if (safeSubset.contains(result.fImage->subset())) {
            result.fBoundary = PixelBoundary::kInitialized;
        }
    }
    return result;
}

void FilterResult::draw(const Context& ctx, SkDevice* target, const SkBlender* blender) const {
    SkAutoDeviceTransformRestore adtr{target, ctx.mapping().layerToDevice()};
    this->draw(ctx, target, /*preserveDeviceState=*/true, blender);
}

void FilterResult::draw(const Context& ctx,
                        SkDevice* device,
                        bool preserveDeviceState,
                        const SkBlender* blender) const {
    const bool blendAffectsTransparentBlack = blender && as_BB(blender)->affectsTransparentBlack();
    if (!fImage) {
        // The image is transparent black, this is a no-op unless we need to apply the blend mode
        if (blendAffectsTransparentBlack) {
            SkPaint clear;
            clear.setColor4f(SkColors::kTransparent);
            clear.setBlender(sk_ref_sp(blender));
            device->drawPaint(clear);
        }
        return;
    }

    BoundsScope scope = blendAffectsTransparentBlack ? BoundsScope::kShaderOnly
                                                     : BoundsScope::kCanDrawDirectly;
    SkEnumBitMask<BoundsAnalysis> analysis = this->analyzeBounds(device->localToDevice(),
                                                                 device->devClipBounds(),
                                                                 scope);

    if (analysis & BoundsAnalysis::kRequiresLayerCrop) {
        if (blendAffectsTransparentBlack) {
            // This is similar to the resolve() path in applyColorFilter() when the filter affects
            // transparent black but must be applied after the prior visible layer bounds clip.
            // NOTE: We map devClipBounds() by the local-to-device matrix instead of the Context
            // mapping because that works for both use cases: drawing to the final device (where
            // the transforms are the same), or drawing to intermediate layer images (where they
            // are not the same).
            LayerSpace<SkIRect> dstBounds;
            if (!LayerSpace<SkMatrix>(device->localToDevice()).inverseMapRect(
                        LayerSpace<SkIRect>(device->devClipBounds()), &dstBounds)) {
                return;
            }
            // Regardless of the scenario, the end result is that it's in layer space.
            FilterResult clipped = this->resolve(ctx, dstBounds);
            clipped.draw(ctx, device, preserveDeviceState, blender);
            return;
        }
        // Otherwise we can apply the layer bounds as a clip to avoid an intermediate render pass
        if (preserveDeviceState) {
            device->pushClipStack();
        }
        device->clipRect(SkRect::Make(SkIRect(fLayerBounds)), SkClipOp::kIntersect, /*aa=*/true);
    }

    // If we are an integer translate, the default bilinear sampling *should* be equivalent to
    // nearest-neighbor. Going through the direct image-drawing path tends to detect this
    // and reduce sampling automatically. When we have to use an image shader, this isn't
    // detected and some GPUs' linear filtering doesn't exactly match nearest-neighbor and can
    // lead to leaks beyond the image's subset. Detect and reduce sampling explicitly.
    const bool pixelAligned =
            is_nearly_integer_translation(fTransform) &&
            is_nearly_integer_translation(skif::LayerSpace<SkMatrix>(device->localToDevice()));
    SkSamplingOptions sampling = fSamplingOptions;
    if (sampling == kDefaultSampling && pixelAligned) {
        sampling = {};
    }

    if (analysis & BoundsAnalysis::kHasLayerFillingEffect ||
        (blendAffectsTransparentBlack && (analysis & BoundsAnalysis::kDstBoundsNotCovered))) {
        // Fill the canvas with the shader, so that the pixels beyond the image dimensions are still
        // covered by the draw and either resolve tiling into the image, color filter transparent
        // black, apply the blend mode to the dst, or any combination thereof.
        SkPaint paint;
        if (!preserveDeviceState && !blender) {
            // When we don't care about the device's prior contents, the default blender can be kSrc
#if !defined(SK_USE_SRCOVER_FOR_FILTERS)
            paint.setBlendMode(SkBlendMode::kSrc);
#endif
        } else {
            paint.setBlender(sk_ref_sp(blender));
        }
        paint.setShader(this->getAnalyzedShaderView(ctx, sampling, analysis));
        device->drawPaint(paint);
    } else {
        SkPaint paint;
        paint.setBlender(sk_ref_sp(blender));
        paint.setColorFilter(fColorFilter);

        // src's origin is embedded in fTransform. For historical reasons, drawSpecial() does
        // not automatically use the device's current local-to-device matrix, but that's what preps
        // it to match the expected layer coordinate system.
        SkMatrix netTransform = SkMatrix::Concat(device->localToDevice(), SkMatrix(fTransform));

        // Check fSamplingOptions for linear filtering, not 'sampling' since it may have been
        // reduced to nearest neighbor.
        if (this->canClampToTransparentBoundary(analysis) && fSamplingOptions == kDefaultSampling) {
            SkASSERT(!(analysis & BoundsAnalysis::kRequiresShaderTiling));
            // Draw non-AA with a 1px outset image so that the transparent boundary filtering is
            // not multiplied with the AA (which creates a harsher AA transition).
            if (!preserveDeviceState && !blender) {
                // Since this is a non-AA draw, kSrc can be more efficient if we are the default
                // blend mode and can assume the prior dst pixels were transparent black.
#if !defined(SK_USE_SRCOVER_FOR_FILTERS)
                paint.setBlendMode(SkBlendMode::kSrc);
#endif
            }
            netTransform.preTranslate(-1.f, -1.f);
            device->drawSpecial(fImage->makePixelOutset().get(), netTransform, sampling, paint,
                                SkCanvas::kFast_SrcRectConstraint);
        } else {
            paint.setAntiAlias(true);
            SkCanvas::SrcRectConstraint constraint = SkCanvas::kFast_SrcRectConstraint;
            if (analysis & BoundsAnalysis::kRequiresShaderTiling) {
                constraint = SkCanvas::kStrict_SrcRectConstraint;
                ctx.markShaderBasedTilingRequired(SkTileMode::kClamp);
            }
            device->drawSpecial(fImage.get(), netTransform, sampling, paint, constraint);
        }
    }

    if (preserveDeviceState && (analysis & BoundsAnalysis::kRequiresLayerCrop)) {
        device->popClipStack();
    }
}

sk_sp<SkShader> FilterResult::asShader(const Context& ctx,
                                       const SkSamplingOptions& xtraSampling,
                                       SkEnumBitMask<ShaderFlags> flags,
                                       const LayerSpace<SkIRect>& sampleBounds) const {
    if (!fImage) {
        return nullptr;
    }
    // Even if flags don't force resolving the filter result to an axis-aligned image, if the
    // extra sampling to be applied is not compatible with the accumulated transform and sampling,
    // or if the logical image is cropped by the layer bounds, the FilterResult will need to be
    // resolved to an image before we wrap it as an SkShader. When checking if cropped, we use the
    // FilterResult's layer bounds instead of the context's desired output, assuming that the layer
    // bounds reflect the bounds of the coords a parent shader will pass to eval().
    const bool currentXformIsInteger = is_nearly_integer_translation(fTransform);
    const bool nextXformIsInteger = !(flags & ShaderFlags::kNonTrivialSampling);

    SkBlendMode colorFilterMode;
    SkEnumBitMask<BoundsAnalysis> analysis = this->analyzeBounds(sampleBounds,
                                                                 BoundsScope::kShaderOnly);

    SkSamplingOptions sampling = xtraSampling;
    const bool needsResolve =
            // Deferred calculations on the input would be repeated with each sample, but we allow
            // simple color filters to skip resolving since their repeated math should be cheap.
            (flags & ShaderFlags::kSampledRepeatedly &&
                    ((fColorFilter && (!fColorFilter->asAColorMode(nullptr, &colorFilterMode) ||
                                       colorFilterMode > SkBlendMode::kLastCoeffMode)) ||
                     !SkColorSpace::Equals(fImage->getColorSpace(), ctx.colorSpace()))) ||
            // The deferred sampling options can't be merged with the one requested
            !compatible_sampling(fSamplingOptions, currentXformIsInteger,
                                 &sampling, nextXformIsInteger) ||
            // The deferred edge of the layer bounds is visible to sampling
            (analysis & BoundsAnalysis::kRequiresLayerCrop);

    // Downgrade to nearest-neighbor if the sequence of sampling doesn't do anything
    if (sampling == kDefaultSampling && nextXformIsInteger &&
        (needsResolve || currentXformIsInteger)) {
        sampling = {};
    }

    sk_sp<SkShader> shader;
    if (needsResolve) {
        // The resolve takes care of fTransform (sans origin), fTileMode, fColorFilter, and
        // fLayerBounds.
        FilterResult resolved = this->resolve(ctx, sampleBounds);
        if (resolved) {
            // Redo the analysis, however, because it's hard to predict HW edge tiling. Since the
            // original layer crop was visible, that implies that the now-resolved image won't cover
            // dst bounds. Since we are using this as a shader to fill the dst bounds, we may have
            // to still do shader-clamping (to a transparent boundary) if the resolved image doesn't
            // have HW-tileable boundaries.
            [[maybe_unused]] static constexpr SkEnumBitMask<BoundsAnalysis> kExpectedAnalysis =
                    BoundsAnalysis::kDstBoundsNotCovered | BoundsAnalysis::kRequiresShaderTiling;
            analysis = resolved.analyzeBounds(sampleBounds, BoundsScope::kShaderOnly);
            SkASSERT(!(analysis & ~kExpectedAnalysis));
            return resolved.getAnalyzedShaderView(ctx, sampling, analysis);
        }
    } else {
        shader = this->getAnalyzedShaderView(ctx, sampling, analysis);
    }

    return shader;
}

sk_sp<SkShader> FilterResult::getAnalyzedShaderView(
        const Context& ctx,
        const SkSamplingOptions& finalSampling,
        SkEnumBitMask<BoundsAnalysis> analysis) const {
    const SkMatrix& localMatrix(fTransform);
    const SkRect imageBounds = SkRect::Make(fImage->dimensions());
    // We need to apply the decal in a coordinate space that matches the resolution of the layer
    // space. If the transform preserves rectangles, map the image bounds by the transform so we
    // can apply it before we evaluate the shader. Otherwise decompose the transform into a
    // non-scaling post-decal transform and a scaling pre-decal transform.
    SkMatrix postDecal, preDecal;
    if (localMatrix.rectStaysRect() ||
        !(analysis & BoundsAnalysis::kRequiresDecalInLayerSpace)) {
        postDecal = SkMatrix::I();
        preDecal = localMatrix;
    } else {
        decompose_transform(localMatrix, imageBounds.center(), &postDecal, &preDecal);
    }

    // If the image covers the dst bounds, then its tiling won't be visible, so we can switch
    // to the faster kClamp for either HW or shader-based tiling. If we are applying the decal
    // in layer space, then that extra shader implements the tiling, so we can switch to clamp
    // for the image shader itself.
    SkTileMode effectiveTileMode = fTileMode;
    const bool decalClampToTransparent = this->canClampToTransparentBoundary(analysis);
    const bool strict = SkToBool(analysis & BoundsAnalysis::kRequiresShaderTiling);

    sk_sp<SkShader> imageShader;
    if (strict && decalClampToTransparent) {
        // Make the image shader apply to the 1px outset so that the strict subset includes the
        // transparent pixels.
        preDecal.preTranslate(-1.f, -1.f);
        imageShader = fImage->makePixelOutset()->asShader(SkTileMode::kClamp, finalSampling,
                                                          preDecal, strict);
        effectiveTileMode = SkTileMode::kClamp;
    } else {
        if (!(analysis & BoundsAnalysis::kDstBoundsNotCovered) ||
            (analysis & BoundsAnalysis::kRequiresDecalInLayerSpace)) {
            effectiveTileMode = SkTileMode::kClamp;
        }
        imageShader = fImage->asShader(effectiveTileMode, finalSampling, preDecal, strict);
    }
    if (strict) {
        ctx.markShaderBasedTilingRequired(effectiveTileMode);
    }

    if (analysis & BoundsAnalysis::kRequiresDecalInLayerSpace) {
        SkASSERT(fTileMode == SkTileMode::kDecal);
        // TODO(skbug:12784) - As part of fully supporting subsets in image shaders, it probably
        // makes sense to share the subset tiling logic that's in GrTextureEffect as dedicated
        // SkShaders. Graphite can then add those to its program as-needed vs. always doing
        // shader-based tiling, and CPU can have raster-pipeline tiling applied more flexibly than
        // at the bitmap level. At that point, this effect is redundant and can be replaced with the
        // decal-subset shader.
        const SkRuntimeEffect* decalEffect =
                GetKnownRuntimeEffect(SkKnownRuntimeEffects::StableKey::kDecal);

        SkRuntimeShaderBuilder builder(sk_ref_sp(decalEffect));
        builder.child("image") = std::move(imageShader);
        builder.uniform("decalBounds") = preDecal.mapRect(imageBounds);

        imageShader = builder.makeShader();
    }

    if (imageShader && (analysis & BoundsAnalysis::kRequiresDecalInLayerSpace)) {
        imageShader = imageShader->makeWithLocalMatrix(postDecal);
    }

    if (imageShader && fColorFilter) {
        imageShader = imageShader->makeWithColorFilter(fColorFilter);
    }

    // Shader now includes the image, the sampling, the tile mode, the transform, and the color
    // filter, skipping deferred effects that aren't present or aren't visible given 'analysis'.
    // The last "effect", layer bounds cropping, must be handled externally by either resolving
    // the image before hand or clipping the device that's drawing the returned shader.
    return imageShader;
}

// FilterResult::rescale() implementation

namespace {

// The following code uses "PixelSpace" as an alias to refer to the LayerSpace of the low-res
// input image and blurred output to differentiate values for the original and final layer space
template <typename T>
using PixelSpace = LayerSpace<T>;

int downscale_step_count(float netScaleFactor) {
    int steps = SkNextLog2(sk_float_ceil2int(1.f / netScaleFactor));
    // There are (steps-1) 1/2x steps and then one step that will be between 1/2-1x. If the
    // final step is practically the identity scale, we can save a render pass and not incur too
    // much sampling error by reducing the step count and using a final scale that's slightly less
    // than 1/2.
    if (steps > 0) {
        // For a multipass rescale, we allow for a lot of tolerance when deciding to collapse the
        // final step. If there's only a single pass, we require the scale factor to be very close
        // to the identity since it causes the step count to go to 0.
        static constexpr float kMultiPassLimit = 0.9f;
        static constexpr float kNearIdentityLimit = 1.f - kRoundEpsilon; // 1px error in 1000px img

        float finalStepScale = netScaleFactor * (1 << (steps - 1));
        float limit = steps == 1 ? kNearIdentityLimit : kMultiPassLimit;
        if (finalStepScale >= limit) {
            steps--;
        }
    }

    return steps;
}

PixelSpace<SkRect> scale_about_center(const PixelSpace<SkRect> src, float sx, float sy) {
    float cx = sx == 1.f ? 0.f : (0.5f * src.left() + 0.5f * src.right());
    float cy = sy == 1.f ? 0.f : (0.5f * src.top()  + 0.5f * src.bottom());
    return LayerSpace<SkRect>({(src.left()  - cx) * sx, (src.top()    - cy) * sy,
                               (src.right() - cx) * sx, (src.bottom() - cy) * sy});
}

void draw_color_filtered_border(SkCanvas* canvas,
                                PixelSpace<SkIRect> border,
                                sk_sp<SkColorFilter> colorFilter) {
    SkPaint cfOnly;
    cfOnly.setColor4f(SkColors::kTransparent);
    cfOnly.setColorFilter(std::move(colorFilter));
#if !defined(SK_USE_SRCOVER_FOR_FILTERS)
    cfOnly.setBlendMode(SkBlendMode::kSrc);
#endif

    canvas->drawIRect({border.left(),      border.top(),
                       border.right(),     border.top() + 1},
                       cfOnly); // Top (with corners)
    canvas->drawIRect({border.left(),      border.bottom() - 1,
                       border.right(),     border.bottom()},
                       cfOnly); // Bottom (with corners)
    canvas->drawIRect({border.left(),      border.top() + 1,
                       border.left() + 1,  border.bottom() - 1},
                       cfOnly); // Left (no corners)
    canvas->drawIRect({border.right() - 1, border.top() + 1,
                       border.right(),     border.bottom() - 1},
                       cfOnly); // Right (no corners)
}

void draw_tiled_border(SkCanvas* canvas,
                       SkTileMode tileMode,
                       const SkPaint& paint,
                       const PixelSpace<SkMatrix>& srcToDst,
                       PixelSpace<SkRect> srcBorder,
                       PixelSpace<SkRect> dstBorder) {
    SkASSERT(tileMode != SkTileMode::kDecal); // There are faster ways for just transparent black

    // Sample the border pixels directly, scaling only on an axis at a time for
    // edges, and with no scaling for corners. Since only the CTM is adjusted, these
    // 8 draws should be batchable with the primary fill that had used `paint`.
    auto drawEdge = [&](const SkRect& src, const SkRect& dst) {
        canvas->save();
        canvas->concat(SkMatrix::RectToRect(src, dst));
        canvas->drawRect(src, paint);
        canvas->restore();
    };
    auto drawCorner = [&](const SkPoint& src, const SkPoint& dst) {
        drawEdge(SkRect::MakeXYWH(src.fX, src.fY, 1.f, 1.f),
                 SkRect::MakeXYWH(dst.fX, dst.fY, 1.f, 1.f));
    };

    // 'dstBorder' includes the 1px padding that we are filling in. Inset to reconstruct the
    // original sampled dst.
    PixelSpace<SkRect> dstSampleBounds{dstBorder};
    dstSampleBounds.inset(PixelSpace<SkSize>({1.f, 1.f}));

    // Reconstruct the original source coordinate bounds
    PixelSpace<SkRect> srcSampleBounds;
    SkAssertResult(srcToDst.inverseMapRect(dstSampleBounds, &srcSampleBounds));

    if (tileMode == SkTileMode::kMirror || tileMode == SkTileMode::kRepeat) {
        // Adjust 'srcBorder' to instead match the 1px rectangle centered over srcSampleBounds
        // in order to calculate the average of the two outermost sampled pixels.
        // Inset by an extra 1/2 so that the eventual sample coordinates average the outermost two
        // rows/columns of src pixels.
        srcBorder = dstSampleBounds;
        srcBorder.inset(PixelSpace<SkSize>({0.5f, 0.5f}));
        SkAssertResult(srcToDst.inverseMapRect(srcBorder, &srcBorder));
        srcBorder.outset(PixelSpace<SkSize>({0.5f, 0.5f}));
    }

    // Invert the dst coordinates for repeat so that the left edge is mapped to the
    // right edge of the output, etc.
    if (tileMode == SkTileMode::kRepeat) {
        dstBorder = PixelSpace<SkRect>({dstBorder.right() - 1.f, dstBorder.bottom() - 1.f,
                                        dstBorder.left()  + 1.f, dstBorder.top()    + 1.f});
    }

    // Edges (excluding corners)
    drawEdge({srcBorder.left(),        srcSampleBounds.top(),
              srcBorder.left() + 1.f,  srcSampleBounds.bottom()},
             {dstBorder.left(),        dstSampleBounds.top(),
              dstBorder.left() + 1.f,  dstSampleBounds.bottom()}); // Left

    drawEdge({srcBorder.right() - 1.f, srcSampleBounds.top(),
              srcBorder.right(),       srcSampleBounds.bottom()},
             {dstBorder.right() - 1.f, dstSampleBounds.top(),
              dstBorder.right(),       dstSampleBounds.bottom()}); // Right

    drawEdge({srcSampleBounds.left(),  srcBorder.top(),
              srcSampleBounds.right(), srcBorder.top() + 1.f},
             {dstSampleBounds.left(),  dstBorder.top(),
              dstSampleBounds.right(), dstBorder.top() + 1.f});    // Top

    drawEdge({srcSampleBounds.left(),  srcBorder.bottom() - 1.f,
              srcSampleBounds.right(), srcBorder.bottom()},
             {dstSampleBounds.left(),  dstBorder.bottom() - 1.f,
              dstSampleBounds.right(), dstBorder.bottom()});       // Bottom

    // Corners (sampled directly to preserve their value since they can dominate the
    // output of a clamped blur with a large radius).
    drawCorner({srcBorder.left(),        srcBorder.top()},
               {dstBorder.left(),        dstBorder.top()});          // TL
    drawCorner({srcBorder.right() - 1.f, srcBorder.top()},
               {dstBorder.right() - 1.f, dstBorder.top()});          // TR
    drawCorner({srcBorder.right() - 1.f, srcBorder.bottom() - 1.f},
               {dstBorder.right() - 1.f, dstBorder.bottom() - 1.f}); // BR
    drawCorner({srcBorder.left(),        srcBorder.bottom() - 1.f},
               {dstBorder.left(),        dstBorder.bottom() - 1.f}); // BL
}

} // anonymous namespace

FilterResult FilterResult::rescale(const Context& ctx,
                                   const LayerSpace<SkSize>& scale,
                                   bool enforceDecal) const {
    LayerSpace<SkIRect> visibleLayerBounds = fLayerBounds;
    if (!fImage || !visibleLayerBounds.intersect(ctx.desiredOutput()) ||
        scale.width() <= 0.f || scale.height() <= 0.f) {
        return {};
    }

    // NOTE: For the first pass, PixelSpace and LayerSpace are equivalent
    PixelSpace<SkIPoint> origin;
    const bool pixelAligned = is_nearly_integer_translation(fTransform, &origin);
    SkEnumBitMask<BoundsAnalysis> analysis = this->analyzeBounds(ctx.desiredOutput(),
                                                                 BoundsScope::kRescale);

    // If there's no actual scaling, and no other effects that have to be resolved for blur(),
    // then just extract the necessary subset. Otherwise fall through and apply the effects with
    // scale factor (possibly identity).
    const bool canDeferTiling =
            pixelAligned &&
            !(analysis & BoundsAnalysis::kRequiresLayerCrop) &&
            !(enforceDecal && (analysis & BoundsAnalysis::kHasLayerFillingEffect));

    // To match legacy color space conversion logic, treat a null src as sRGB and a null dst as
    // as the src CS.
    const SkColorSpace* srcCS = fImage->getColorSpace() ? fImage->getColorSpace()
                                                        : sk_srgb_singleton();
    const SkColorSpace* dstCS = ctx.colorSpace() ? ctx.colorSpace() : srcCS;
    const bool hasEffectsToApply =
            !canDeferTiling ||
            SkToBool(fColorFilter) ||
            fImage->colorType() != ctx.backend()->colorType() ||
            !SkColorSpace::Equals(srcCS, dstCS);

    int xSteps = downscale_step_count(scale.width());
    int ySteps = downscale_step_count(scale.height());
    if (xSteps == 0 && ySteps == 0 && !hasEffectsToApply) {
        if (analysis & BoundsAnalysis::kHasLayerFillingEffect) {
            // At this point, the only effects that could be visible is a non-decal mode, so just
            // return the image with adjusted layer bounds to match desired output.
            FilterResult noop = *this;
            noop.fLayerBounds = visibleLayerBounds;
            return noop;
        } else {
            // The visible layer bounds represents a tighter bounds than the image itself
            return this->subset(origin, visibleLayerBounds);
        }
    }

    PixelSpace<SkIRect> srcRect;
    SkTileMode tileMode;
    bool cfBorder = false;
    bool deferPeriodicTiling = false;
    if (canDeferTiling && (analysis & BoundsAnalysis::kHasLayerFillingEffect)) {
        // When we can defer tiling, and said tiling is visible, rescaling the original image
        // uses smaller textures.
        srcRect = LayerSpace<SkIRect>(SkIRect::MakeXYWH(origin.x(), origin.y(),
                                                        fImage->width(), fImage->height()));
        if (fTileMode == SkTileMode::kDecal &&
            (analysis & BoundsAnalysis::kHasLayerFillingEffect)) {
            // Like in applyColorFilter() evaluate the transparent CF'ed border and clamp to it.
            tileMode = SkTileMode::kClamp;
            cfBorder = true;
        } else {
            tileMode = fTileMode;
            deferPeriodicTiling = tileMode == SkTileMode::kRepeat ||
                                  tileMode == SkTileMode::kMirror;
        }
    } else {
        // Otherwise we either have to rescale the layer-bounds-sized image (!canDeferTiling)
        // or the tiling isn't visible so the layer bounds represents a smaller effective
        // image than the original image data.
        srcRect = visibleLayerBounds;
        tileMode = SkTileMode::kDecal;
    }

    srcRect = srcRect.relevantSubset(ctx.desiredOutput(), tileMode);
    // To avoid incurring error from rounding up the dimensions at every step, the logical size of
    // the image is tracked in floats through the whole process; rounding to integers is only done
    // to produce a conservative pixel buffer and clamp-tiling is used so that partially covered
    // pixels are filled with the un-weighted color.
    PixelSpace<SkRect> stepBoundsF{srcRect};
    if (stepBoundsF.isEmpty()) {
        return {};
    }
    // stepPixelBounds holds integer pixel values (as floats) and includes any padded outsetting
    // that was rendered by the previous step, while stepBoundsF does not have any padding.
    PixelSpace<SkRect> stepPixelBounds{srcRect};

    // If we made it here, at least one iteration is required, even if xSteps and ySteps are 0.
    FilterResult image = *this;
    if (!pixelAligned && (xSteps > 0 || ySteps > 0)) {
        // If the source image has a deferred transform with a downscaling factor, we don't want to
        // necessarily compose the first rescale step's transform with it because we will then be
        // missing pixels in the bilinear filtering and create sampling artifacts during animations.
        // NOTE: Force nextSteps counts to the max integer value when the accumulated scale factor
        // is not finite, to force the input image to be resolved.
        LayerSpace<SkSize> netScale = image.fTransform.mapSize(scale);
        int nextXSteps = std::isfinite(netScale.width()) ? downscale_step_count(netScale.width())
                                                         : std::numeric_limits<int>::max();
        int nextYSteps = std::isfinite(netScale.height()) ? downscale_step_count(netScale.height())
                                                          : std::numeric_limits<int>::max();
        // We only need to resolve the deferred transform if the rescaling along an axis is not
        // near identity (steps > 0). If it's near identity, there's no real difference in sampling
        // between resolving here and deferring it to the first rescale iteration.
        if ((xSteps > 0 && nextXSteps > xSteps) || (ySteps > 0 && nextYSteps > ySteps)) {
            // Resolve the deferred transform. We don't just fold the deferred scale factor into
            // the rescaling steps because, for better or worse, the deferred transform does not
            // otherwise participate in progressive scaling so we should be consistent.
            image = image.resolve(ctx, srcRect);
            if (!image) {
                // Early out if the resolve failed
                return {};
            }
            if (!cfBorder) {
                // This sets the resolved image to match either kDecal or the deferred tile mode.
                image.fTileMode = tileMode;
            } // else leave it as kDecal when cfBorder is true
        }
    }

    // For now, if we are deferring periodic tiling, we need to ensure that the low-res image bounds
    // are pixel aligned. This is because the tiling is applied at the pixel level in SkImageShader,
    // and we need the period of the low-res image to align with the original high-resolution period
    // If/when SkImageShader supports shader-tiling over fractional bounds, this can relax.
    float finalScaleX = xSteps > 0 ? scale.width() : 1.f;
    float finalScaleY = ySteps > 0 ? scale.height() : 1.f;
    if (deferPeriodicTiling) {
        PixelSpace<SkRect> dstBoundsF = scale_about_center(stepBoundsF, finalScaleX, finalScaleY);
        // Use a pixel bounds that's smaller than what was requested to ensure any post-blur amount
        // is lower than the max supported. In the event that roundIn() would collapse to an empty
        // rect, use a 1x1 bounds that contains the center point.
        PixelSpace<SkIRect> innerDstPixels = dstBoundsF.roundIn();
        int dstCenterX = sk_float_floor2int(0.5f * dstBoundsF.right()  + 0.5f * dstBoundsF.left());
        int dstCenterY = sk_float_floor2int(0.5f * dstBoundsF.bottom() + 0.5f * dstBoundsF.top());
        dstBoundsF = PixelSpace<SkRect>({(float) std::min(dstCenterX,   innerDstPixels.left()),
                                         (float) std::min(dstCenterY,   innerDstPixels.top()),
                                         (float) std::max(dstCenterX+1, innerDstPixels.right()),
                                         (float) std::max(dstCenterY+1, innerDstPixels.bottom())});

        finalScaleX = dstBoundsF.width() / srcRect.width();
        finalScaleY = dstBoundsF.height() / srcRect.height();

        // Recompute how many steps are needed, as we may need to do one more step from the round-in
        xSteps = downscale_step_count(finalScaleX);
        ySteps = downscale_step_count(finalScaleY);

        // The periodic tiling effect will be manually rendered into the lower resolution image so
        // that clamp tiling can be used at each decimation.
        image.fTileMode = SkTileMode::kClamp;
    }

    do {
        float sx = 1.f;
        if (xSteps > 0) {
            sx = xSteps > 1 ? 0.5f : srcRect.width()*finalScaleX / stepBoundsF.width();
            xSteps--;
        }

        float sy = 1.f;
        if (ySteps > 0) {
            sy = ySteps > 1 ? 0.5f : srcRect.height()*finalScaleY / stepBoundsF.height();
            ySteps--;
        }

        // Downscale relative to the center of the image, which better distributes any sort of
        // sampling errors across the image (vs. emphasizing the bottom right edges).
        PixelSpace<SkRect> dstBoundsF = scale_about_center(stepBoundsF, sx, sy);

        // NOTE: Rounding out is overly conservative when dstBoundsF has an odd integer width/height
        // but with coordinates at 1/2. In this case, we could create a pixel grid that has a
        // fractional translation in the final FilterResult but that will best be done when
        // FilterResult tracks floating bounds.
        PixelSpace<SkIRect> dstPixelBounds = dstBoundsF.roundOut();

        PixelBoundary boundary = PixelBoundary::kUnknown;
        PixelSpace<SkIRect> sampleBounds = dstPixelBounds;
        if (tileMode == SkTileMode::kDecal) {
            boundary = PixelBoundary::kTransparent;
        } else {
            // This is roughly equivalent to using PixelBoundary::kInitialized, but keeps some of
            // the later logic simpler.
            dstPixelBounds.outset(LayerSpace<SkISize>({1,1}));
        }

        AutoSurface surface{ctx, dstPixelBounds, boundary, /*renderInParameterSpace=*/false};
        if (surface) {
            const auto scaleXform = PixelSpace<SkMatrix>::RectToRect(stepBoundsF, dstBoundsF);

            // Redo analysis with the actual scale transform and padded low res bounds.
            // With the padding added to dstPixelBounds, intermediate steps should not require
            // shader tiling. Unfortunately, when the last step requires a scale factor other than
            // 1/2, shader based clamping may still be necessary with just a single pixel of padding
            // TODO: Given that the final step may often require shader-based tiling, it may make
            // sense to tile into a large enough texture that the subsequent blurs will not require
            // any shader-based tiling.
            analysis = image.analyzeBounds(SkMatrix(scaleXform),
                                           SkIRect(sampleBounds),
                                           BoundsScope::kRescale);

            // Primary fill that will cover all of 'sampleBounds'
            SkPaint paint;
            paint.setShader(image.getAnalyzedShaderView(ctx, image.sampling(), analysis));
#if !defined(SK_USE_SRCOVER_FOR_FILTERS)
            paint.setBlendMode(SkBlendMode::kSrc);
#endif

            PixelSpace<SkRect> srcSampled;
            SkAssertResult(scaleXform.inverseMapRect(PixelSpace<SkRect>(sampleBounds),
                                                     &srcSampled));

            surface->save();
                surface->concat(SkMatrix(scaleXform));
                surface->drawRect(SkRect(srcSampled), paint);
            surface->restore();

            if (cfBorder) {
                // Fill in the border with the transparency-affecting color filter, which is
                // what the image shader's tile mode would have produced anyways but this avoids
                // triggering shader-based tiling.
                SkASSERT(fColorFilter && as_CFB(fColorFilter)->affectsTransparentBlack());
                SkASSERT(tileMode == SkTileMode::kClamp);

                draw_color_filtered_border(surface.canvas(), dstPixelBounds, fColorFilter);
                // Clamping logic will preserve its values on subsequent rescale steps.
                cfBorder = false;
            } else if (tileMode != SkTileMode::kDecal) {
                // Draw the edges of the shader into the padded border, respecting the tile mode
                draw_tiled_border(surface.canvas(), tileMode, paint, scaleXform,
                                  stepPixelBounds, PixelSpace<SkRect>(dstPixelBounds));
            }
        } else {
            // Rescaling can't complete, no sense in downscaling non-existent data
            return {};
        }

        image = surface.snap();
        // If we are deferring periodic tiling, use kClamp on subsequent steps to preserve the
        // border pixels. The original tile mode will be restored at the end.
        image.fTileMode = deferPeriodicTiling ? SkTileMode::kClamp : tileMode;

        stepBoundsF = dstBoundsF;
        stepPixelBounds = PixelSpace<SkRect>(dstPixelBounds);
    } while(xSteps > 0 || ySteps > 0);


    // Rebuild the downscaled image, including a transform back to the original layer-space
    // resolution, restoring the layer bounds it should fill, and setting tile mode.
    if (deferPeriodicTiling) {
        // Inset the image to undo the manually added border of pixels, which will allow the result
        // to have the kInitialized boundary state.
        image = image.insetByPixel();
    } else {
        SkASSERT(tileMode == SkTileMode::kDecal || tileMode == SkTileMode::kClamp);
        // Leave the image as-is. If it's decal tiled, this preserves the known transparent
        // boundary. If it's clamp tiled, we want to clamp to the carefully maintained boundary
        // pixels that better preserved the original boundary. Taking a subset like we did for
        // periodic tiles would effectively clamp to the interior of the image.
    }
    image.fTileMode = tileMode;
    image.fTransform.postConcat(
            LayerSpace<SkMatrix>::RectToRect(stepBoundsF, LayerSpace<SkRect>{srcRect}));
    image.fLayerBounds = visibleLayerBounds;

    SkASSERT(!enforceDecal || image.fTileMode == SkTileMode::kDecal);
    SkASSERT(image.fTileMode != SkTileMode::kDecal ||
             image.fBoundary == PixelBoundary::kTransparent);
    SkASSERT(!deferPeriodicTiling || image.fBoundary == PixelBoundary::kInitialized);
    return image;
}

FilterResult FilterResult::MakeFromPicture(const Context& ctx,
                                           sk_sp<SkPicture> pic,
                                           ParameterSpace<SkRect> cullRect) {
    SkASSERT(pic);
    LayerSpace<SkIRect> dstBounds = ctx.mapping().paramToLayer(cullRect).roundOut();
    if (!dstBounds.intersect(ctx.desiredOutput())) {
        return {};
    }

    // Given the standard usage of the picture image filter (i.e., to render content at a fixed
    // resolution that, most likely, differs from the screen's) disable LCD text by removing any
    // knowledge of the pixel geometry.
    // TODO: Should we just generally do this for layers with image filters? Or can we preserve it
    // for layers that are still axis-aligned?
    SkSurfaceProps props = ctx.backend()->surfaceProps()
                                         .cloneWithPixelGeometry(kUnknown_SkPixelGeometry);
    // TODO(b/329700315): The SkPicture may contain dithered content, which would be affected by any
    // boundary padding. Until we can control the dither origin, force it to have no padding.
    AutoSurface surface{ctx, dstBounds, PixelBoundary::kUnknown,
                        /*renderInParameterSpace=*/true, &props};
    if (surface) {
        surface->clipRect(SkRect(cullRect));
        surface->drawPicture(std::move(pic));
    }
    return surface.snap();
}

FilterResult FilterResult::MakeFromShader(const Context& ctx,
                                          sk_sp<SkShader> shader,
                                          bool dither) {
    SkASSERT(shader);

    // TODO(b/329700315): Using a boundary other than unknown shifts the origin of dithering, which
    // complicates layout test validation in chrome. Until we can control the dither origin,
    // force dithered shader FilterResults to have no padding.
    PixelBoundary boundary = dither ? PixelBoundary::kUnknown : PixelBoundary::kTransparent;
    AutoSurface surface{ctx, ctx.desiredOutput(), boundary, /*renderInParameterSpace=*/true};
    if (surface) {
        SkPaint paint;
        paint.setShader(shader);
        paint.setDither(dither);
#if !defined(SK_USE_SRCOVER_FOR_FILTERS)
        paint.setBlendMode(SkBlendMode::kSrc);
#endif
        surface->drawPaint(paint);
    }
    return surface.snap();
}

FilterResult FilterResult::MakeFromImage(const Context& ctx,
                                         sk_sp<SkImage> image,
                                         SkRect srcRect,
                                         ParameterSpace<SkRect> dstRect,
                                         const SkSamplingOptions& sampling) {
    SkASSERT(image);

    SkRect imageBounds = SkRect::Make(image->dimensions());
    if (!imageBounds.contains(srcRect)) {
        SkMatrix srcToDst = SkMatrix::RectToRect(srcRect, SkRect(dstRect));
        if (!srcRect.intersect(imageBounds)) {
            return {}; // No overlap, so return an empty/transparent image
        }
        // Adjust dstRect to match the updated srcRect
        dstRect = ParameterSpace<SkRect>{srcToDst.mapRect(srcRect)};
    }

    if (SkRect(dstRect).isEmpty()) {
        return {}; // Output collapses to empty
    }

    // Check for direct conversion to an SkSpecialImage and then FilterResult. Eventually this
    // whole function should be replaceable with:
    //    FilterResult(fImage, fSrcRect, fDstRect).applyTransform(mapping.layerMatrix(), fSampling);
    SkIRect srcSubset = RoundOut(srcRect);
    if (SkRect::Make(srcSubset) == srcRect) {
        // Construct an SkSpecialImage from the subset directly instead of drawing.
        sk_sp<SkSpecialImage> specialImage = ctx.backend()->makeImage(srcSubset, std::move(image));

        // Treat the srcRect's top left as "layer" space since we are folding the src->dst transform
        // and the param->layer transform into a single transform step. We don't override the
        // PixelBoundary from kUnknown even if srcRect is contained within the 'image' because the
        // client could be doing their own external approximate-fit texturing.
        skif::FilterResult subset{std::move(specialImage),
                                  skif::LayerSpace<SkIPoint>(srcSubset.topLeft())};
        SkM44 transform = ctx.mapping().layerMatrix() * SkM44::RectToRect(srcRect, SkRect(dstRect));
        return subset.applyTransform(ctx, skif::LayerSpace<SkMatrix>(transform.asM33()), sampling);
    }

    // For now, draw the src->dst subset of image into a new image.
    LayerSpace<SkIRect> dstBounds = ctx.mapping().paramToLayer(dstRect).roundOut();
    if (!dstBounds.intersect(ctx.desiredOutput())) {
        return {};
    }

    AutoSurface surface{ctx, dstBounds, PixelBoundary::kTransparent,
                        /*renderInParameterSpace=*/true};
    if (surface) {
        SkPaint paint;
        paint.setAntiAlias(true);
        surface->drawImageRect(std::move(image), srcRect, SkRect(dstRect), sampling, &paint,
                               SkCanvas::kStrict_SrcRectConstraint);
    }
    return surface.snap();
}

///////////////////////////////////////////////////////////////////////////////////////////////////
// FilterResult::Builder

FilterResult::Builder::Builder(const Context& context) : fContext(context) {}
FilterResult::Builder::~Builder() = default;

SkSpan<sk_sp<SkShader>> FilterResult::Builder::createInputShaders(
        const LayerSpace<SkIRect>& outputBounds,
        bool evaluateInParameterSpace) {
    SkEnumBitMask<ShaderFlags> xtraFlags = ShaderFlags::kNone;
    SkMatrix layerToParam;
    if (evaluateInParameterSpace) {
        // The FilterResult is meant to be sampled in layer space, but the shader this is feeding
        // into is being sampled in parameter space. Add the inverse of the layerMatrix() (i.e.
        // layer to parameter space) as a local matrix to convert from the parameter-space coords
        // of the outer shader to the layer-space coords of the FilterResult).
        SkAssertResult(fContext.mapping().layerMatrix().asM33().invert(&layerToParam));
        // Automatically add nonTrivial sampling if the layer-to-parameter space mapping isn't
        // also pixel aligned.
        if (!is_nearly_integer_translation(LayerSpace<SkMatrix>(layerToParam))) {
            xtraFlags |= ShaderFlags::kNonTrivialSampling;
        }
    }

    fInputShaders.reserve(fInputs.size());
    for (const SampledFilterResult& input : fInputs) {
        // Assume the input shader will be evaluated once per pixel in the output unless otherwise
        // specified when the FilterResult was added to the builder.
        auto sampleBounds = input.fSampleBounds ? *input.fSampleBounds : outputBounds;
        auto shader = input.fImage.asShader(fContext,
                                            input.fSampling,
                                            input.fFlags | xtraFlags,
                                            sampleBounds);
        if (evaluateInParameterSpace && shader) {
            shader = shader->makeWithLocalMatrix(layerToParam);
        }
        fInputShaders.push_back(std::move(shader));
    }
    return SkSpan<sk_sp<SkShader>>(fInputShaders);
}

LayerSpace<SkIRect> FilterResult::Builder::outputBounds(
        std::optional<LayerSpace<SkIRect>> explicitOutput) const {
    // Pessimistically assume output fills the full desired bounds
    LayerSpace<SkIRect> output = fContext.desiredOutput();
    if (explicitOutput.has_value()) {
        // Intersect with the provided explicit bounds
        if (!output.intersect(*explicitOutput)) {
            return LayerSpace<SkIRect>::Empty();
        }
    }
    return output;
}

FilterResult FilterResult::Builder::drawShader(sk_sp<SkShader> shader,
                                               const LayerSpace<SkIRect>& outputBounds,
                                               bool evaluateInParameterSpace) const {
    SkASSERT(!outputBounds.isEmpty()); // Should have been rejected before we created shaders
    if (!shader) {
        return {};
    }

    AutoSurface surface{fContext, outputBounds, PixelBoundary::kTransparent,
                        evaluateInParameterSpace};
    if (surface) {
        SkPaint paint;
        paint.setShader(std::move(shader));
#if !defined(SK_USE_SRCOVER_FOR_FILTERS)
        paint.setBlendMode(SkBlendMode::kSrc);
#endif
        surface->drawPaint(paint);
    }
    return surface.snap();
}

FilterResult FilterResult::Builder::merge() {
    // merge() could return an empty image on 0 added inputs, but this should have been caught
    // earlier and routed to SkImageFilters::Empty() instead.
    SkASSERT(!fInputs.empty());
    if (fInputs.size() == 1) {
        SkASSERT(!fInputs[0].fSampleBounds.has_value() &&
                 fInputs[0].fSampling == kDefaultSampling &&
                 fInputs[0].fFlags == ShaderFlags::kNone);
        return fInputs[0].fImage;
    }

    const auto mergedBounds = LayerSpace<SkIRect>::Union(
            (int) fInputs.size(),
            [this](int i) { return fInputs[i].fImage.layerBounds(); });
    const auto outputBounds = this->outputBounds(mergedBounds);

    AutoSurface surface{fContext, outputBounds, PixelBoundary::kTransparent,
                        /*renderInParameterSpace=*/false};
    if (surface) {
        for (const SampledFilterResult& input : fInputs) {
            SkASSERT(!input.fSampleBounds.has_value() &&
                     input.fSampling == kDefaultSampling &&
                     input.fFlags == ShaderFlags::kNone);
            input.fImage.draw(fContext, surface.device(), /*preserveDeviceState=*/true);
        }
    }
    return surface.snap();
}

FilterResult FilterResult::Builder::blur(const LayerSpace<SkSize>& sigma) {
    SkASSERT(fInputs.size() == 1);

    // TODO: The blur functor is only supported for GPU contexts; SkBlurImageFilter should have
    // detected this.
    const SkBlurEngine* blurEngine = fContext.backend()->getBlurEngine();
    SkASSERT(blurEngine);

    const SkBlurEngine::Algorithm* algorithm = blurEngine->findAlgorithm(
            SkSize(sigma), fContext.backend()->colorType());
    if (!algorithm) {
        return {};
    }

    // TODO: De-duplicate this logic between SkBlurImageFilter, here, and skgpu::BlurUtils.
    LayerSpace<SkISize> radii =
            LayerSpace<SkSize>({3.f*sigma.width(), 3.f*sigma.height()}).ceil();
    auto maxOutput = fInputs[0].fImage.layerBounds();
    maxOutput.outset(radii);

    auto outputBounds = this->outputBounds(maxOutput);
    if (outputBounds.isEmpty()) {
        return {};
    }

    // These are the source pixels that will be read from the input image, which can be calculated
    // internally because the blur's access pattern is well defined (vs. needing it to be provided
    // in Builder::add()).
    auto sampleBounds = outputBounds;
    sampleBounds.outset(radii);

    if (fContext.backend()->useLegacyFilterResultBlur()) {
        SkASSERT(sigma.width() <= algorithm->maxSigma() && sigma.height() <= algorithm->maxSigma());

        FilterResult resolved = fInputs[0].fImage.resolve(fContext, sampleBounds);
        if (!resolved) {
            return {};
        }
        auto srcRelativeOutput = outputBounds;
        srcRelativeOutput.offset(-resolved.layerBounds().topLeft());
        resolved = {algorithm->blur(SkSize(sigma),
                                    resolved.fImage,
                                    SkIRect::MakeSize(resolved.fImage->dimensions()),
                                    SkTileMode::kDecal,
                                    SkIRect(srcRelativeOutput)),
                    outputBounds.topLeft()};
        return resolved;
    }

    float sx = sigma.width()  > algorithm->maxSigma() ? algorithm->maxSigma()/sigma.width()  : 1.f;
    float sy = sigma.height() > algorithm->maxSigma() ? algorithm->maxSigma()/sigma.height() : 1.f;
    // For identity scale factors, this rescale() is a no-op when possible, but otherwise it will
    // also handle resolving any color filters or transform similar to a resolve() except that it
    // can defer the tile mode.
    FilterResult lowResImage = fInputs[0].fImage.rescale(
            fContext.withNewDesiredOutput(sampleBounds),
            LayerSpace<SkSize>({sx, sy}),
            algorithm->supportsOnlyDecalTiling());
    if (!lowResImage) {
        return {};
    }
    SkASSERT(lowResImage.tileMode() == SkTileMode::kDecal ||
             !algorithm->supportsOnlyDecalTiling());

    // Map 'sigma' into the low-res image's pixel space to determine the low-res blur params to pass
    // into the blur engine. This relies on rescale() producing an image with a scale+translate
    // transform, so it's possible to derive the inverse scale factors directly. We also clamp to
    // be <= maxSigma just in case floating point error made it slightly higher.
    const float invScaleX = sk_ieee_float_divide(1.f, lowResImage.fTransform.rc(0,0));
    const float invScaleY = sk_ieee_float_divide(1.f, lowResImage.fTransform.rc(1,1));
    PixelSpace<SkSize> lowResSigma{{std::min(sigma.width() * invScaleX, algorithm->maxSigma()),
                                    std::min(sigma.height()* invScaleY, algorithm->maxSigma())}};
    PixelSpace<SkIRect> lowResMaxOutput{SkISize{lowResImage.fImage->width(),
                                                lowResImage.fImage->height()}};

    PixelSpace<SkIRect> srcRelativeOutput;
    if (lowResImage.tileMode() == SkTileMode::kRepeat ||
        lowResImage.tileMode() == SkTileMode::kMirror) {
        // The periodic tiling was deferred when down-sampling; we can further defer it to after the
        // blur. The low-res output is 1-to-1 with the low res image.
        srcRelativeOutput = lowResMaxOutput;
    } else {
        // For decal and clamp tiling, the blurred image stops being interesting outside the radii
        // outset, so redo the max output analysis with the 'outputBounds' mapped into pixel space.
        SkAssertResult(lowResImage.fTransform.inverseMapRect(outputBounds, &srcRelativeOutput));

        // NOTE: Since 'lowResMaxOutput' is based on the actual image and deferred tiling, this can
        // be smaller than the pessimistic filling for a clamp-tiled blur.
        lowResMaxOutput.outset(PixelSpace<SkSize>({3.f * lowResSigma.width(),
                                                   3.f * lowResSigma.height()}).ceil());
        srcRelativeOutput = lowResMaxOutput.relevantSubset(srcRelativeOutput,
                                                           lowResImage.tileMode());

        // Clamp won't return empty from relevantSubset() and a non-intersecting decal should have
        // been caught earlier.
        // TODO(40042624): However, with some pathological inputs and the current mix of float vs.
        // int representations, the definition of emptiness can change. Once everything is floating
        // point, this check can be removed.
        if (srcRelativeOutput.isEmpty()) {
            return {};
        }

        // Include 1px of blur output so that it can be sampled during the upscale, which is needed
        // to correctly seam large blurs across crop/raster tiles (crbug.com/1500021).
        srcRelativeOutput.outset(PixelSpace<SkISize>({1, 1}));
    }

    sk_sp<SkSpecialImage> lowResBlur = lowResImage.refImage();
    SkIRect blurOutputBounds = SkIRect(srcRelativeOutput);
    SkTileMode tileMode = lowResImage.tileMode();
    if (!algorithm->supportsOnlyDecalTiling() &&
        lowResImage.canClampToTransparentBoundary(BoundsAnalysis::kSimple)) {
        // Have to manage this manually since the BlurEngine isn't aware of the known pixel padding.
        lowResBlur = lowResBlur->makePixelOutset();
        // This offset() is intentional; `blurOutputBounds` already includes an outset from an
        // earlier modification of `srcRelativeOutput`. This offset is to align the SkBlurAlgorithm
        // output bounds with the adjusted source image.
        blurOutputBounds.offset(1, 1);
        tileMode = SkTileMode::kClamp;
    }

    lowResBlur = algorithm->blur(SkSize(lowResSigma),
                                 lowResBlur,
                                 SkIRect::MakeSize(lowResBlur->dimensions()),
                                 tileMode,
                                 blurOutputBounds);
    if (!lowResBlur) {
        // The blur output bounds may exceed max texture size even if the source image did not.
        // TODO(b/377932106): Can we handle this more gracefully by rendering a smaller image and
        // then transforming it to fill the large space?
        return {};
    }

    FilterResult result{std::move(lowResBlur), srcRelativeOutput.topLeft()};
    if (lowResImage.tileMode() == SkTileMode::kClamp ||
        lowResImage.tileMode() == SkTileMode::kDecal) {
        // Undo the outset padding that was added to srcRelativeOutput before invoking the blur
        result = result.insetByPixel();
    }

    result.fTransform.postConcat(lowResImage.fTransform);
    if (lowResImage.tileMode() == SkTileMode::kDecal) {
        // Recalculate the output bounds based on the blur output; with rounding the final image may
        // be slightly larger than the original, which would unnecessarily add cropping to the layer
        // bounds. But so long as the `outputBounds` had been constrained by the input's own layer,
        // that crop is unnecessary. The result is still restricted to the desired output bounds,
        // which will induce clipping as needed for a rounded-out image.
        outputBounds = this->outputBounds(
                result.fTransform.mapRect(LayerSpace<SkIRect>(result.fImage->dimensions())));
    }
    result.fLayerBounds = outputBounds;
    result.fTileMode = lowResImage.tileMode();
    return result;
}

} // end namespace skif