src/utils/SkNinePatch.cpp

/*
 * Copyright 2006 The Android Open Source Project
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */


#include "SkNinePatch.h"
#include "SkCanvas.h"
#include "SkShader.h"

static const uint16_t g3x3Indices[] = {
    0, 5, 1,    0, 4, 5,
    1, 6, 2,    1, 5, 6,
    2, 7, 3,    2, 6, 7,

    4, 9, 5,    4, 8, 9,
    5, 10, 6,   5, 9, 10,
    6, 11, 7,   6, 10, 11,

    8, 13, 9,   8, 12, 13,
    9, 14, 10,  9, 13, 14,
    10, 15, 11, 10, 14, 15
};

static int fillIndices(uint16_t indices[], int xCount, int yCount) {
    uint16_t* startIndices = indices;

    int n = 0;
    for (int y = 0; y < yCount; y++) {
        for (int x = 0; x < xCount; x++) {
            *indices++ = n;
            *indices++ = n + xCount + 2;
            *indices++ = n + 1;

            *indices++ = n;
            *indices++ = n + xCount + 1;
            *indices++ = n + xCount + 2;

            n += 1;
        }
        n += 1;
    }
    return static_cast<int>(indices - startIndices);
}

// Computes the delta between vertices along a single axis
static SkScalar computeVertexDelta(bool isStretchyVertex,
                                   SkScalar currentVertex,
                                   SkScalar prevVertex,
                                   SkScalar stretchFactor) {
    // the standard delta between vertices if no stretching is required
    SkScalar delta = currentVertex - prevVertex;

    // if the stretch factor is negative or zero we need to shrink the 9-patch
    // to fit within the target bounds.  This means that we will eliminate all
    // stretchy areas and scale the fixed areas to fit within the target bounds.
    if (stretchFactor <= 0) {
        if (isStretchyVertex)
            delta = 0; // collapse stretchable areas
        else
            delta = SkScalarMul(delta, -stretchFactor); // scale fixed areas
    // if the stretch factor is positive then we use the standard delta for
    // fixed and scale the stretchable areas to fill the target bounds.
    } else if (isStretchyVertex) {
        delta = SkScalarMul(delta, stretchFactor);
    }

    return delta;
}

static void fillRow(SkPoint verts[], SkPoint texs[],
                    const SkScalar vy, const SkScalar ty,
                    const SkRect& bounds, const int32_t xDivs[], int numXDivs,
                    const SkScalar stretchX, int width) {
    SkScalar vx = bounds.fLeft;
    verts->set(vx, vy); verts++;
    texs->set(0, ty); texs++;

    SkScalar prev = 0;
    for (int x = 0; x < numXDivs; x++) {

        const SkScalar tx = SkIntToScalar(xDivs[x]);
        vx += computeVertexDelta(x & 1, tx, prev, stretchX);
        prev = tx;

        verts->set(vx, vy); verts++;
        texs->set(tx, ty); texs++;
    }
    verts->set(bounds.fRight, vy); verts++;
    texs->set(SkIntToScalar(width), ty); texs++;
}

struct Mesh {
    const SkPoint*  fVerts;
    const SkPoint*  fTexs;
    const SkColor*  fColors;
    const uint16_t* fIndices;
};

void SkNinePatch::DrawMesh(SkCanvas* canvas, const SkRect& bounds,
                           const SkBitmap& bitmap,
                           const int32_t xDivs[], int numXDivs,
                           const int32_t yDivs[], int numYDivs,
                           const SkPaint* paint) {
    if (bounds.isEmpty() || bitmap.width() == 0 || bitmap.height() == 0) {
        return;
    }

    // should try a quick-reject test before calling lockPixels
    SkAutoLockPixels alp(bitmap);
    // after the lock, it is valid to check
    if (!bitmap.readyToDraw()) {
        return;
    }

    // check for degenerate divs (just an optimization, not required)
    {
        int i;
        int zeros = 0;
        for (i = 0; i < numYDivs && yDivs[i] == 0; i++) {
            zeros += 1;
        }
        numYDivs -= zeros;
        yDivs += zeros;
        for (i = numYDivs - 1; i >= 0 && yDivs[i] == bitmap.height(); --i) {
            numYDivs -= 1;
        }
    }

    Mesh mesh;

    const int numXStretch = (numXDivs + 1) >> 1;
    const int numYStretch = (numYDivs + 1) >> 1;

    if (numXStretch < 1 && numYStretch < 1) {
        canvas->drawBitmapRect(bitmap, bounds, paint);
        return;
    }

    if (false) {
        int i;
        for (i = 0; i < numXDivs; i++) {
            SkDebugf("--- xdivs[%d] %d\n", i, xDivs[i]);
        }
        for (i = 0; i < numYDivs; i++) {
            SkDebugf("--- ydivs[%d] %d\n", i, yDivs[i]);
        }
    }

    SkScalar stretchX = 0, stretchY = 0;

    if (numXStretch > 0) {
        int stretchSize = 0;
        for (int i = 1; i < numXDivs; i += 2) {
            stretchSize += xDivs[i] - xDivs[i-1];
        }
        const SkScalar fixed = SkIntToScalar(bitmap.width() - stretchSize);
        if (bounds.width() >= fixed)
            stretchX = (bounds.width() - fixed) / stretchSize;
        else // reuse stretchX, but keep it negative as a signal
            stretchX = -bounds.width() / fixed;
    }

    if (numYStretch > 0) {
        int stretchSize = 0;
        for (int i = 1; i < numYDivs; i += 2) {
            stretchSize += yDivs[i] - yDivs[i-1];
        }
        const SkScalar fixed = SkIntToScalar(bitmap.height() - stretchSize);
        if (bounds.height() >= fixed)
            stretchY = (bounds.height() - fixed) / stretchSize;
        else // reuse stretchX, but keep it negative as a signal
            stretchY = -bounds.height() / fixed;
    }

#if 0
    SkDebugf("---- drawasamesh [%d %d] -> [%g %g] <%d %d> (%g %g)\n",
             bitmap.width(), bitmap.height(),
             SkScalarToFloat(bounds.width()), SkScalarToFloat(bounds.height()),
             numXDivs + 1, numYDivs + 1,
             SkScalarToFloat(stretchX), SkScalarToFloat(stretchY));
#endif

    const int vCount = (numXDivs + 2) * (numYDivs + 2);
    // number of celss * 2 (tris per cell) * 3 (verts per tri)
    const int indexCount = (numXDivs + 1) * (numYDivs + 1) * 2 * 3;
    // allocate 2 times, one for verts, one for texs, plus indices
    SkAutoMalloc storage(vCount * sizeof(SkPoint) * 2 +
                         indexCount * sizeof(uint16_t));
    SkPoint* verts = (SkPoint*)storage.get();
    SkPoint* texs = verts + vCount;
    uint16_t* indices = (uint16_t*)(texs + vCount);

    mesh.fVerts = verts;
    mesh.fTexs = texs;
    mesh.fColors = nullptr;
    mesh.fIndices = nullptr;

    // we use <= for YDivs, since the prebuild indices work for 3x2 and 3x1 too
    if (numXDivs == 2 && numYDivs <= 2) {
        mesh.fIndices = g3x3Indices;
    } else {
        SkDEBUGCODE(int n =) fillIndices(indices, numXDivs + 1, numYDivs + 1);
        SkASSERT(n == indexCount);
        mesh.fIndices = indices;
    }

    SkScalar vy = bounds.fTop;
    fillRow(verts, texs, vy, 0, bounds, xDivs, numXDivs,
            stretchX, bitmap.width());
    verts += numXDivs + 2;
    texs += numXDivs + 2;
    for (int y = 0; y < numYDivs; y++) {
        const SkScalar ty = SkIntToScalar(yDivs[y]);
        if (stretchY >= 0) {
            if (y & 1) {
                vy += stretchY;
            } else {
                vy += ty;
            }
        } else {    // shrink fixed sections, and collaps stretchy sections
            if (y & 1) {
                ;// do nothing
            } else {
                vy += SkScalarMul(ty, -stretchY);
            }
        }
        fillRow(verts, texs, vy, ty, bounds, xDivs, numXDivs,
                stretchX, bitmap.width());
        verts += numXDivs + 2;
        texs += numXDivs + 2;
    }
    fillRow(verts, texs, bounds.fBottom, SkIntToScalar(bitmap.height()),
            bounds, xDivs, numXDivs, stretchX, bitmap.width());

    SkShader* shader = SkShader::CreateBitmapShader(bitmap,
                                                    SkShader::kClamp_TileMode,
                                                    SkShader::kClamp_TileMode);
    SkPaint p;
    if (paint) {
        p = *paint;
    }
    p.setShader(shader)->unref();
    canvas->drawVertices(SkCanvas::kTriangles_VertexMode, vCount,
                         mesh.fVerts, mesh.fTexs, mesh.fColors, nullptr,
                         mesh.fIndices, indexCount, p);
}

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

static void drawNineViaRects(SkCanvas* canvas, const SkRect& dst,
                             const SkBitmap& bitmap, const SkIRect& margins,
                             const SkPaint* paint) {
    const int32_t srcX[4] = {
        0, margins.fLeft, bitmap.width() - margins.fRight, bitmap.width()
    };
    const int32_t srcY[4] = {
        0, margins.fTop, bitmap.height() - margins.fBottom, bitmap.height()
    };
    SkScalar dstX[4] = {
        dst.fLeft, dst.fLeft + SkIntToScalar(margins.fLeft),
        dst.fRight - SkIntToScalar(margins.fRight), dst.fRight
    };
    SkScalar dstY[4] = {
        dst.fTop, dst.fTop + SkIntToScalar(margins.fTop),
        dst.fBottom - SkIntToScalar(margins.fBottom), dst.fBottom
    };

    if (dstX[1] > dstX[2]) {
        dstX[1] = dstX[0] + (dstX[3] - dstX[0]) * SkIntToScalar(margins.fLeft) /
            (SkIntToScalar(margins.fLeft) + SkIntToScalar(margins.fRight));
        dstX[2] = dstX[1];
    }

    if (dstY[1] > dstY[2]) {
        dstY[1] = dstY[0] + (dstY[3] - dstY[0]) * SkIntToScalar(margins.fTop) /
            (SkIntToScalar(margins.fTop) + SkIntToScalar(margins.fBottom));
        dstY[2] = dstY[1];
    }

    SkIRect s;
    SkRect  d;
    for (int y = 0; y < 3; y++) {
        s.fTop = srcY[y];
        s.fBottom = srcY[y+1];
        d.fTop = dstY[y];
        d.fBottom = dstY[y+1];
        for (int x = 0; x < 3; x++) {
            s.fLeft = srcX[x];
            s.fRight = srcX[x+1];
            d.fLeft = dstX[x];
            d.fRight = dstX[x+1];
            canvas->drawBitmapRect(bitmap, s, d, paint);
        }
    }
}

void SkNinePatch::DrawNine(SkCanvas* canvas, const SkRect& bounds,
                           const SkBitmap& bitmap, const SkIRect& margins,
                           const SkPaint* paint) {
    /** Our vertices code has numerical precision problems if the transformed
     coordinates land directly on a 1/2 pixel boundary. To work around that
     for now, we only take the vertices case if we are in opengl. Also,
     when not in GL, the vertices impl is slower (more math) than calling
     the viaRects code.
     */
    if (false /* is our canvas backed by a gpu?*/) {
        int32_t xDivs[2];
        int32_t yDivs[2];

        xDivs[0] = margins.fLeft;
        xDivs[1] = bitmap.width() - margins.fRight;
        yDivs[0] = margins.fTop;
        yDivs[1] = bitmap.height() - margins.fBottom;

        if (xDivs[0] > xDivs[1]) {
            xDivs[0] = bitmap.width() * margins.fLeft /
                (margins.fLeft + margins.fRight);
            xDivs[1] = xDivs[0];
        }
        if (yDivs[0] > yDivs[1]) {
            yDivs[0] = bitmap.height() * margins.fTop /
                (margins.fTop + margins.fBottom);
            yDivs[1] = yDivs[0];
        }

        SkNinePatch::DrawMesh(canvas, bounds, bitmap,
                              xDivs, 2, yDivs, 2, paint);
    } else {
        drawNineViaRects(canvas, bounds, bitmap, margins, paint);
    }
}