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// This controls the range of values added to color channels
layout(key) in int rangeType;
@make {
static std::unique_ptr<GrFragmentProcessor> Make(GrPixelConfig dstConfig) {
int rangeType;
switch (dstConfig) {
case kGray_8_GrPixelConfig:
case kRGBA_8888_GrPixelConfig:
case kBGRA_8888_GrPixelConfig:
case kSRGBA_8888_GrPixelConfig:
case kSBGRA_8888_GrPixelConfig:
rangeType = 0;
break;
case kRGB_565_GrPixelConfig:
rangeType = 1;
break;
case kRGBA_4444_GrPixelConfig:
rangeType = 2;
break;
case kUnknown_GrPixelConfig:
case kAlpha_half_GrPixelConfig:
case kRGBA_8888_sint_GrPixelConfig:
case kRGBA_float_GrPixelConfig:
case kRG_float_GrPixelConfig:
case kRGBA_half_GrPixelConfig:
case kAlpha_8_GrPixelConfig:
return nullptr;
}
return std::unique_ptr<GrFragmentProcessor>(new GrDitherEffect(rangeType));
}
}
void main() {
half value;
half range;
@switch (rangeType) {
case 0:
range = 1.0 / 255.0;
break;
case 1:
range = 1.0 / 63.0;
break;
default:
// Experimentally this looks better than the expected value of 1/15.
range = 1.0 / 15.0;
break;
}
@if (sk_Caps.integerSupport) {
// This ordered-dither code is lifted from the cpu backend.
uint x = uint(sk_FragCoord.x);
uint y = uint(sk_FragCoord.y);
uint m = (y & 1) << 5 | (x & 1) << 4 |
(y & 2) << 2 | (x & 2) << 1 |
(y & 4) >> 1 | (x & 4) >> 2;
value = half(m) * 1.0 / 64.0 - 63.0 / 128.0;
} else {
// Simulate the integer effect used above using step/mod. For speed, simulates a 4x4
// dither pattern rather than an 8x8 one.
half4 modValues = mod(sk_FragCoord.xyxy, half4(2.0, 2.0, 4.0, 4.0));
half4 stepValues = step(modValues, half4(1.0, 1.0, 2.0, 2.0));
value = dot(stepValues, half4(8.0 / 16.0, 4.0 / 16.0, 2.0 / 16.0, 1.0 / 16.0)) - 15.0 / 32.0;
}
// For each color channel, add the random offset to the channel value and then clamp
// between 0 and alpha to keep the color premultiplied.
sk_OutColor = half4(clamp(sk_InColor.rgb + value * range, 0, sk_InColor.a), sk_InColor.a);
}
@test(testData) {
float range = testData->fRandom->nextRangeF(0.001f, 0.05f);
return std::unique_ptr<GrFragmentProcessor>(new GrDitherEffect(range));
}
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