Bowing my head in shame, going back to gamma interpolated gradients

Frankengradients (linearly interpolated RGB, gamma interpolated alpha) look
fantastic but unfortunately create sligh compatibility issues. For instance,
a gradient from 0xffea1030 to 0x00ea1030 (opaque to alpha, with a single
color) blended on top of 0xff101010 would not look the same as a single
opaque gradient from 0xffea1030 to 0xff101010. The difference is hardly
noticeable on simple gradients but it could cause confusion amongst app
developers. Their life is hard enough as it is, let's be good to them.

My crusade against the gamma world is not over and one day I shall
be the victor. I am patience.

Bug: 35485208
Test: UiRendering.ShaderTests, UiRendering.GradientTests, manual testing
Change-Id: I8204e60cdf0a6b12dfe22638d30ca9622687000e

1 files changed, 22 insertions, 19 deletions

diff --git a/libs/hwui/ProgramCache.cpp b/libs/hwui/ProgramCache.cpp
index 3f842e0b5679..38c23e4babe8 100644
--- a/libs/hwui/ProgramCache.cpp
+++ b/libs/hwui/ProgramCache.cpp
@@ -202,23 +202,26 @@ const char* gFS_Gradient_Functions = R"__SHADER__(
 )__SHADER__";
 const char* gFS_Gradient_Preamble[2] = {
         // Linear framebuffer
-        "\nvec4 dither(const vec4 color) {\n"
-        "    return color + (triangleNoise(gl_FragCoord.xy * screenSize.xy) / 255.0);\n"
-        "}\n"
-        "\nvec4 gammaMix(const vec4 a, const vec4 b, float v) {\n"
-        "    vec4 c = mix(a, b, v);\n"
-        "    c.a = EOTF_sRGB(c.a);\n" // This is technically incorrect but preserves compatibility
-        "    return vec4(OETF_sRGB(c.rgb) * c.a, c.a);\n"
-        "}\n",
+        R"__SHADER__(
+        vec4 dither(const vec4 color) {
+            return color + (triangleNoise(gl_FragCoord.xy * screenSize.xy) / 255.0);
+        }
+        vec4 gradientMix(const vec4 a, const vec4 b, float v) {
+            vec4 c = mix(a, b, v);
+            return vec4(c.rgb * c.a, c.a);
+        }
+        )__SHADER__",
         // sRGB framebuffer
-        "\nvec4 dither(const vec4 color) {\n"
-        "    vec3 dithered = sqrt(color.rgb) + (triangleNoise(gl_FragCoord.xy * screenSize.xy) / 255.0);\n"
-        "    return vec4(dithered * dithered, color.a);\n"
-        "}\n"
-        "\nvec4 gammaMix(const vec4 a, const vec4 b, float v) {\n"
-        "    vec4 c = mix(a, b, v);\n"
-        "    return vec4(c.rgb * c.a, c.a);\n"
-        "}\n"
+        R"__SHADER__(
+        vec4 dither(const vec4 color) {
+            vec3 dithered = sqrt(color.rgb) + (triangleNoise(gl_FragCoord.xy * screenSize.xy) / 255.0);
+            return vec4(dithered * dithered, color.a);
+        }
+        vec4 gradientMixMix(const vec4 a, const vec4 b, float v) {
+            vec4 c = mix(a, b, v);
+            return vec4(c.rgb * c.a, c.a);
+        }
+        )__SHADER__",
 };
 
 // Uses luminance coefficients from Rec.709 to choose the appropriate gamma
@@ -272,19 +275,19 @@ const char* gFS_Main_FetchGradient[6] = {
         // Linear
         "    vec4 gradientColor = texture2D(gradientSampler, linear);\n",
 
-        "    vec4 gradientColor = gammaMix(startColor, endColor, clamp(linear, 0.0, 1.0));\n",
+        "    vec4 gradientColor = gradientMix(startColor, endColor, clamp(linear, 0.0, 1.0));\n",
 
         // Circular
         "    vec4 gradientColor = texture2D(gradientSampler, vec2(length(circular), 0.5));\n",
 
-        "    vec4 gradientColor = gammaMix(startColor, endColor, clamp(length(circular), 0.0, 1.0));\n",
+        "    vec4 gradientColor = gradientMix(startColor, endColor, clamp(length(circular), 0.0, 1.0));\n",
 
         // Sweep
         "    highp float index = atan(sweep.y, sweep.x) * 0.15915494309; // inv(2 * PI)\n"
         "    vec4 gradientColor = texture2D(gradientSampler, vec2(index - floor(index), 0.5));\n",
 
         "    highp float index = atan(sweep.y, sweep.x) * 0.15915494309; // inv(2 * PI)\n"
-        "    vec4 gradientColor = gammaMix(startColor, endColor, clamp(index - floor(index), 0.0, 1.0));\n"
+        "    vec4 gradientColor = gradientMix(startColor, endColor, clamp(index - floor(index), 0.0, 1.0));\n"
 };
 const char* gFS_Main_FetchBitmap =
         "    vec4 bitmapColor = OETF(texture2D(bitmapSampler, outBitmapTexCoords));\n";