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>
diff --git a/src/gpu/effects/GrDitherEffect.cpp b/src/gpu/effects/GrDitherEffect.cpp
index 17b94ff..f2fc678 100644
--- a/src/gpu/effects/GrDitherEffect.cpp
+++ b/src/gpu/effects/GrDitherEffect.cpp
@@ -27,13 +27,14 @@
"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)",