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      1 /*
      2  * Copyright 2018 Google Inc.
      3  *
      4  * Use of this source code is governed by a BSD-style license that can be
      5  * found in the LICENSE file.
      6  */
      7 
      8 // This controls the range of values added to color channels
      9 layout(key) in int rangeType;
     10 
     11 @make {
     12     static std::unique_ptr<GrFragmentProcessor> Make(GrPixelConfig dstConfig) {
     13         int rangeType;
     14         switch (dstConfig) {
     15             case kGray_8_GrPixelConfig:
     16             case kGray_8_as_Lum_GrPixelConfig:
     17             case kGray_8_as_Red_GrPixelConfig:
     18             case kRGBA_8888_GrPixelConfig:
     19             case kBGRA_8888_GrPixelConfig:
     20             case kSRGBA_8888_GrPixelConfig:
     21             case kSBGRA_8888_GrPixelConfig:
     22                 rangeType = 0;
     23                 break;
     24             case kRGB_565_GrPixelConfig:
     25                 rangeType = 1;
     26                 break;
     27             case kRGBA_4444_GrPixelConfig:
     28                 rangeType = 2;
     29                 break;
     30             case kUnknown_GrPixelConfig:
     31             case kAlpha_half_GrPixelConfig:
     32             case kAlpha_half_as_Red_GrPixelConfig:
     33             case kRGBA_8888_sint_GrPixelConfig:
     34             case kRGBA_float_GrPixelConfig:
     35             case kRG_float_GrPixelConfig:
     36             case kRGBA_half_GrPixelConfig:
     37             case kAlpha_8_GrPixelConfig:
     38             case kAlpha_8_as_Alpha_GrPixelConfig:
     39             case kAlpha_8_as_Red_GrPixelConfig:
     40                 return nullptr;
     41         }
     42         return std::unique_ptr<GrFragmentProcessor>(new GrDitherEffect(rangeType));
     43     }
     44 }
     45 
     46 void main() {
     47     half value;
     48     half range;
     49     @switch (rangeType) {
     50         case 0:
     51             range = 1.0 / 255.0;
     52             break;
     53         case 1:
     54             range = 1.0 / 63.0;
     55             break;
     56         default:
     57             // Experimentally this looks better than the expected value of 1/15.
     58             range = 1.0 / 15.0;
     59             break;
     60     }
     61     @if (sk_Caps.integerSupport) {
     62         // This ordered-dither code is lifted from the cpu backend.
     63         uint x = uint(sk_FragCoord.x);
     64         uint y = uint(sk_FragCoord.y);
     65         uint m = (y & 1) << 5 | (x & 1) << 4 |
     66                  (y & 2) << 2 | (x & 2) << 1 |
     67                  (y & 4) >> 1 | (x & 4) >> 2;
     68         value = half(m) * 1.0 / 64.0 - 63.0 / 128.0;
     69     } else {
     70         // Simulate the integer effect used above using step/mod. For speed, simulates a 4x4
     71         // dither pattern rather than an 8x8 one.
     72         half4 modValues = mod(sk_FragCoord.xyxy, half4(2.0, 2.0, 4.0, 4.0));
     73         half4 stepValues = step(modValues, half4(1.0, 1.0, 2.0, 2.0));
     74         value = dot(stepValues, half4(8.0 / 16.0, 4.0 / 16.0, 2.0 / 16.0, 1.0 / 16.0)) - 15.0 / 32.0;
     75     }
     76     // For each color channel, add the random offset to the channel value and then clamp
     77     // between 0 and alpha to keep the color premultiplied.
     78     sk_OutColor = half4(clamp(sk_InColor.rgb + value * range, 0, sk_InColor.a), sk_InColor.a);
     79 }
     80 
     81 @test(testData) {
     82     float range = testData->fRandom->nextRangeF(0.001f, 0.05f);
     83     return std::unique_ptr<GrFragmentProcessor>(new GrDitherEffect(range));
     84 }
     85