/* * Copyright 2018 Google Inc. * * Use of this source code is governed by a BSD-style license that can be * found in the LICENSE file. */ // Unrolled gradient code supporting up to 8 intervals that produces code // targeting a specific interval count. // Assumed to be between 1 and 8. layout(key) in int intervalCount; // With the current hardstop detection threshold of 0.00024, the maximum scale and bias values // will be on the order of 4k (since they divide by dt). That is well outside the precision // capabilities of half floats, which can lead to inaccurate gradient calculations layout(ctype=SkPMColor4f) in uniform float4 scale0_1; layout(ctype=SkPMColor4f, when=intervalCount > 1) in uniform float4 scale2_3; layout(ctype=SkPMColor4f, when=intervalCount > 2) in uniform float4 scale4_5; layout(ctype=SkPMColor4f, when=intervalCount > 3) in uniform float4 scale6_7; layout(ctype=SkPMColor4f, when=intervalCount > 4) in uniform float4 scale8_9; layout(ctype=SkPMColor4f, when=intervalCount > 5) in uniform float4 scale10_11; layout(ctype=SkPMColor4f, when=intervalCount > 6) in uniform float4 scale12_13; layout(ctype=SkPMColor4f, when=intervalCount > 7) in uniform float4 scale14_15; layout(ctype=SkPMColor4f) in uniform float4 bias0_1; layout(ctype=SkPMColor4f, when=intervalCount > 1) in uniform float4 bias2_3; layout(ctype=SkPMColor4f, when=intervalCount > 2) in uniform float4 bias4_5; layout(ctype=SkPMColor4f, when=intervalCount > 3) in uniform float4 bias6_7; layout(ctype=SkPMColor4f, when=intervalCount > 4) in uniform float4 bias8_9; layout(ctype=SkPMColor4f, when=intervalCount > 5) in uniform float4 bias10_11; layout(ctype=SkPMColor4f, when=intervalCount > 6) in uniform float4 bias12_13; layout(ctype=SkPMColor4f, when=intervalCount > 7) in uniform float4 bias14_15; // The 7 threshold positions that define the boundaries of the 8 intervals (excluding t = 0, and t = // 1) are packed into two half4's instead of having up to 7 separate scalar uniforms. For low // interval counts, the extra components are ignored in the shader, but the uniform simplification // is worth it. It is assumed thresholds are provided in increasing value, mapped as: // - thresholds1_7.x = boundary between (0,1) and (2,3) -> 1_2 // - .y = boundary between (2,3) and (4,5) -> 3_4 // - .z = boundary between (4,5) and (6,7) -> 5_6 // - .w = boundary between (6,7) and (8,9) -> 7_8 // - thresholds9_13.x = boundary between (8,9) and (10,11) -> 9_10 // - .y = boundary between (10,11) and (12,13) -> 11_12 // - .z = boundary between (12,13) and (14,15) -> 13_14 // - .w = unused in uniform half4 thresholds1_7; in uniform half4 thresholds9_13; void main() { half t = sk_InColor.x; float4 scale, bias; // Explicit binary search for the proper interval that t falls within. The interval count // checks are converted into constant expressions in the C++ generated SkSL, which are then // optimized to the minimal number of branches for the specific interval count. // thresholds1_7.w is mid point for intervals (0,7) and (8,15) if (intervalCount <= 4 || t < thresholds1_7.w) { // thresholds1_7.y is mid point for intervals (0,3) and (4,7) if (intervalCount <= 2 || t < thresholds1_7.y) { // thresholds1_7.x is mid point for intervals (0,1) and (2,3) if (intervalCount <= 1 || t < thresholds1_7.x) { scale = scale0_1; bias = bias0_1; } else { scale = scale2_3; bias = bias2_3; } } else { // thresholds1_7.z is mid point for intervals (4,5) and (6,7) if (intervalCount <= 3 || t < thresholds1_7.z) { scale = scale4_5; bias = bias4_5; } else { scale = scale6_7; bias = bias6_7; } } } else { // thresholds9_13.y is mid point for intervals (8,11) and (12,15) if (intervalCount <= 6 || t < thresholds9_13.y) { // thresholds9_13.x is mid point for intervals (8,9) and (10,11) if (intervalCount <= 5 || t < thresholds9_13.x) { // interval 8-9 scale = scale8_9; bias = bias8_9; } else { // interval 10-11 scale = scale10_11; bias = bias10_11; } } else { // thresholds9_13.z is mid point for intervals (12,13) and (14,15) if (intervalCount <= 7 || t < thresholds9_13.z) { // interval 12-13 scale = scale12_13; bias = bias12_13; } else { // interval 14-15 scale = scale14_15; bias = bias14_15; } } } sk_OutColor = half4(t * scale + bias); } ////////////////////////////////////////////////////////////////////////////// @class { static const int kMaxColorCount = 16; } @make { static std::unique_ptr Make(const SkPMColor4f* colors, const SkScalar* positions, int count); } @cppEnd { static const int kMaxIntervals = 8; std::unique_ptr GrUnrolledBinaryGradientColorizer::Make( const SkPMColor4f* colors, const SkScalar* positions, int count) { // Depending on how the positions resolve into hard stops or regular stops, the number of // intervals specified by the number of colors/positions can change. For instance, a plain // 3 color gradient is two intervals, but a 4 color gradient with a hard stop is also // two intervals. At the most extreme end, an 8 interval gradient made entirely of hard // stops has 16 colors. if (count > kMaxColorCount) { // Definitely cannot represent this gradient configuration return nullptr; } // The raster implementation also uses scales and biases, but since they must be calculated // after the dst color space is applied, it limits our ability to cache their values. SkPMColor4f scales[kMaxIntervals]; SkPMColor4f biases[kMaxIntervals]; SkScalar thresholds[kMaxIntervals]; int intervalCount = 0; for (int i = 0; i < count - 1; i++) { if (intervalCount >= kMaxIntervals) { // Already reached kMaxIntervals, and haven't run out of color stops so this // gradient cannot be represented by this shader. return nullptr; } SkScalar t0 = positions[i]; SkScalar t1 = positions[i + 1]; SkScalar dt = t1 - t0; // If the interval is empty, skip to the next interval. This will automatically create // distinct hard stop intervals as needed. It also protects against malformed gradients // that have repeated hard stops at the very beginning that are effectively unreachable. if (SkScalarNearlyZero(dt)) { continue; } auto c0 = Sk4f::Load(colors[i].vec()); auto c1 = Sk4f::Load(colors[i + 1].vec()); auto scale = (c1 - c0) / dt; auto bias = c0 - t0 * scale; scale.store(scales + intervalCount); bias.store(biases + intervalCount); thresholds[intervalCount] = t1; intervalCount++; } // For isEqual to make sense, set the unused values to something consistent for (int i = intervalCount; i < kMaxIntervals; i++) { scales[i] = SK_PMColor4fTRANSPARENT; biases[i] = SK_PMColor4fTRANSPARENT; thresholds[i] = 0.0; } return std::unique_ptr(new GrUnrolledBinaryGradientColorizer( intervalCount, scales[0], scales[1], scales[2], scales[3], scales[4], scales[5], scales[6], scales[7], biases[0], biases[1], biases[2], biases[3], biases[4], biases[5], biases[6], biases[7], SkRect::MakeLTRB(thresholds[0], thresholds[1], thresholds[2], thresholds[3]), SkRect::MakeLTRB(thresholds[4], thresholds[5], thresholds[6], 0.0))); } }