Pre-multiply gradient colors the right way
Alpha pre-multiplication must be done after applying the
opto-electronic transfer function when linear blending is
disabled. The correct way would be to pre-multiply before
gamma encoding but this leads to improper blending which
cannot be corrected without using sRGB frame buffers and
texture sampling.
Bug: 33010587
Test: cts-tradefed run singleCommand cts-dev --module CtsUiRenderingTestCases --test android.uirendering.cts.testclasses.GradientTests
Change-Id: I5f04bda4cb9f63674537aef5931621c14d601884
diff --git a/libs/hwui/ProgramCache.cpp b/libs/hwui/ProgramCache.cpp
index 0c2309f..2688ba4 100644
--- a/libs/hwui/ProgramCache.cpp
+++ b/libs/hwui/ProgramCache.cpp
@@ -175,10 +175,11 @@
const char* gFS_Gradient_Preamble[2] = {
// Linear framebuffer
"\nvec4 dither(const vec4 color) {\n"
- " return vec4(color.rgb + (triangleNoise(gl_FragCoord.xy * screenSize.xy) / 255.0), color.a);"
+ " return vec4(color.rgb + (triangleNoise(gl_FragCoord.xy * screenSize.xy) / 255.0), color.a);\n"
"}\n"
"\nvec4 gammaMix(const vec4 a, const vec4 b, float v) {\n"
- " return pow(mix(a, b, v), vec4(vec3(1.0 / 2.2), 1.0));"
+ " vec4 c = pow(mix(a, b, v), vec4(vec3(1.0 / 2.2), 1.0));\n"
+ " return vec4(c.rgb * c.a, c.a);\n"
"}\n",
// sRGB framebuffer
"\nvec4 dither(const vec4 color) {\n"
@@ -186,7 +187,8 @@
" return vec4(dithered * dithered, color.a);\n"
"}\n"
"\nvec4 gammaMix(const vec4 a, const vec4 b, float v) {\n"
- " return mix(a, b, v);"
+ " vec4 c = mix(a, b, v);\n"
+ " return vec4(c.rgb * c.a, c.a);\n"
"}\n"
};