Fix HWUI/Skia Gradients to premultiply the colors prior to interpolation

This is fixed in Skia by passing the appropriate flag when the shader is
generated.  The fix in HWUI is to reverse the premultiplication and
interpolation steps.

Test: bit CtsUiRenderingTestCases:.testclasses.ShaderTests
Bug: 34323783
Change-Id: I3417141949f62fcc696b6d8213a4b446d7d0cbf8

1 files changed, 12 insertions, 12 deletions

diff --git a/libs/hwui/GradientCache.cpp b/libs/hwui/GradientCache.cpp
index dceb28518db3..d4d0c997be11 100644
--- a/libs/hwui/GradientCache.cpp
+++ b/libs/hwui/GradientCache.cpp
@@ -189,9 +189,9 @@ void GradientCache::mixBytes(const FloatColor& start, const FloatColor& end,
         float amount, uint8_t*& dst) const {
     float oppAmount = 1.0f - amount;
     float a = start.a * oppAmount + end.a * amount;
-    *dst++ = uint8_t(a * OECF(start.r * oppAmount + end.r * amount) * 255.0f);
-    *dst++ = uint8_t(a * OECF(start.g * oppAmount + end.g * amount) * 255.0f);
-    *dst++ = uint8_t(a * OECF(start.b * oppAmount + end.b * amount) * 255.0f);
+    *dst++ = uint8_t(OECF(start.r * oppAmount + end.r * amount) * 255.0f);
+    *dst++ = uint8_t(OECF(start.g * oppAmount + end.g * amount) * 255.0f);
+    *dst++ = uint8_t(OECF(start.b * oppAmount + end.b * amount) * 255.0f);
     *dst++ = uint8_t(a * 255.0f);
 }
 
@@ -202,13 +202,13 @@ void GradientCache::mixFloats(const FloatColor& start, const FloatColor& end,
     float* d = (float*) dst;
 #ifdef ANDROID_ENABLE_LINEAR_BLENDING
     // We want to stay linear
-    *d++ = a * (start.r * oppAmount + end.r * amount);
-    *d++ = a * (start.g * oppAmount + end.g * amount);
-    *d++ = a * (start.b * oppAmount + end.b * amount);
+    *d++ = (start.r * oppAmount + end.r * amount);
+    *d++ = (start.g * oppAmount + end.g * amount);
+    *d++ = (start.b * oppAmount + end.b * amount);
 #else
-    *d++ = a * OECF(start.r * oppAmount + end.r * amount);
-    *d++ = a * OECF(start.g * oppAmount + end.g * amount);
-    *d++ = a * OECF(start.b * oppAmount + end.b * amount);
+    *d++ = OECF(start.r * oppAmount + end.r * amount);
+    *d++ = OECF(start.g * oppAmount + end.g * amount);
+    *d++ = OECF(start.b * oppAmount + end.b * amount);
 #endif
     *d++ = a;
     dst += 4 * sizeof(float);
@@ -229,10 +229,10 @@ void GradientCache::generateTexture(uint32_t* colors, float* positions,
     ChannelMixer mix = gMixers[mUseFloatTexture];
 
     FloatColor start;
-    start.setUnPreMultiplied(colors[0]);
+    start.set(colors[0]);
 
     FloatColor end;
-    end.setUnPreMultiplied(colors[1]);
+    end.set(colors[1]);
 
     int currentPos = 1;
     float startPos = positions[0];
@@ -247,7 +247,7 @@ void GradientCache::generateTexture(uint32_t* colors, float* positions,
 
             currentPos++;
 
-            end.setUnPreMultiplied(colors[currentPos]);
+            end.set(colors[currentPos]);
             distance = positions[currentPos] - startPos;
         }