diff options
| author |  Eric Karl <ericrk@chromium.org> | 2017-08-07 15:55:13 -0700 |
|---|---|---|
| committer |  Skia Commit-Bot <skia-commit-bot@chromium.org> | 2017-08-09 17:43:25 +0000 |
| commit | e1fc9ac0453470cae2b76f3d22443b9a13ef0811 (patch) | |
| tree | a5981b3fb172c56a540b8343d9ffb051ebf1a38b /src | |
| parent | 7e59e391efc82585cbacbd8223a4aaf5ae632b42 (diff) | |
Improve float-based dither logic
This code simulates the integer-based ordered-dither using step/mod
with only floating point values. Produces similar results.
R=bsalomon@google.com
Bug: skia:4430
Change-Id: I1406f751f0ddd6bfd14e532dfb4efc0bb5784992
Reviewed-on: https://skia-review.googlesource.com/28942
Commit-Queue: Eric Karl <ericrk@chromium.org>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Diffstat (limited to 'src')
| -rw-r--r-- | src/gpu/effects/GrDitherEffect.cpp | 11 | ||||
| -rw-r--r-- | src/gpu/effects/GrDitherEffect.fp | 14 |
2 files changed, 12 insertions, 13 deletions
diff --git a/src/gpu/effects/GrDitherEffect.cpp b/src/gpu/effects/GrDitherEffect.cpp index 17b94ff087..f2fc6784a2 100644 --- a/src/gpu/effects/GrDitherEffect.cpp +++ b/src/gpu/effects/GrDitherEffect.cpp @@ -27,13 +27,14 @@ public: "float value;\nfloat range;\n@switch (%d) {\n case 0:\n range = " "0.0039215686274509803;\n break;\n case 1:\n range = " "0.015873015873015872;\n break;\n default:\n range = " - "0.0083333333333333332;\n break;\n}\n@if (sk_Caps.integerSupport) {\n " + "0.066666666666666666;\n break;\n}\n@if (sk_Caps.integerSupport) {\n " "uint x = uint(sk_FragCoord.x);\n uint y = uint(sk_FragCoord.y);\n uint m = " "(((((y & 1) << 5 | (x & 1) << 4) | (y & 2) << 2) | (x & 2) << 1) | (y & 4) >> 1) " - "| (x & 4) >> 2;\n value = float(m) / 64.0 - 0.4921875;\n} else {\n value = " - "fract(sin(dot(sk_FragCoord.xy, float2(12.989800000000001, 78.233000000000004))) * " - "43758.545299999998) - 0.5;\n}\n%s = float4(clamp(%s.xyz + value * range, 0.0, " - "%s.w), %s.w);\n", + "| (x & 4) >> 2;\n value = float(m) / 64.0 - 0.4921875;\n} else {\n float4 " + "modValues = mod(sk_FragCoord.xyxy, float4(2.0, 2.0, 4.0, 4.0));\n float4 " + "stepValues = step(modValues, float4(1.0, 1.0, 2.0, 2.0));\n value = " + "dot(stepValues, float4(0.5, 0.25, 0.125, 0.0625)) - 0.46875;\n}\n%s = " + "float4(clamp(%s.xyz + value * range, 0.0, %s.w), %s.w);\n", _outer.rangeType(), args.fOutputColor, args.fInputColor ? args.fInputColor : "float4(1)", args.fInputColor ? args.fInputColor : "float4(1)", diff --git a/src/gpu/effects/GrDitherEffect.fp b/src/gpu/effects/GrDitherEffect.fp index 308e02ed43..7ec852e6b0 100644 --- a/src/gpu/effects/GrDitherEffect.fp +++ b/src/gpu/effects/GrDitherEffect.fp @@ -43,7 +43,7 @@ void main() { break; default: // Experimentally this looks better than the expected value of 1/15. - range = 0.125 / 15.0; + range = 1.0 / 15.0; break; } @if (sk_Caps.integerSupport) { @@ -55,13 +55,11 @@ void main() { (y & 4) >> 1 | (x & 4) >> 2; value = float(m) * 1.0 / 64.0 - 63.0 / 128.0; } else { - // Generate a random number based on the fragment position. For this - // random number generator, we use the "GLSL rand" function - // that seems to be floating around on the internet. It works under - // the assumption that sin(<big number>) oscillates with high frequency - // and sampling it will generate "randomness". Since we're using this - // for rendering and not cryptography it should be OK. - value = fract(sin(dot(sk_FragCoord.xy, float2(12.9898, 78.233))) * 43758.5453) - .5; + // Simulate the integer effect used above using step/mod. For speed, simulates a 4x4 + // dither pattern rather than an 8x8 one. + float4 modValues = mod(sk_FragCoord.xyxy, float4(2.0, 2.0, 4.0, 4.0)); + float4 stepValues = step(modValues, float4(1.0, 1.0, 2.0, 2.0)); + value = dot(stepValues, float4(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. |