Handle premultiplication correctly for ColorMatrixColorFilters

bug:17405627

Previously, the input content to the color matrix computation was left
premultiplied. Since the color matrix could reduce the alpha channel,
the alpha was re-multiplied, but this was incomplete, and incorrect.

Instead, apply the color matrix in unpremultiplied space.

Change-Id: I87b8e03d2e228e6ded81f7bbfea952605d7a095c

2 files changed, 5 insertions, 1 deletions

diff --git a/libs/hwui/ProgramCache.cpp b/libs/hwui/ProgramCache.cpp
index a8b8b16..06353c0 100644
--- a/libs/hwui/ProgramCache.cpp
+++ b/libs/hwui/ProgramCache.cpp
@@ -327,8 +327,10 @@ const char* gFS_Main_ApplyColorOp[3] = {
         // None
         "",
         // Matrix
+        "    fragColor.rgb /= (fragColor.a + 0.0019);\n" // un-premultiply
         "    fragColor *= colorMatrix;\n"
-        "    fragColor += colorMatrixVector;\n",
+        "    fragColor += colorMatrixVector;\n"
+        "    fragColor.rgb *= (fragColor.a + 0.0019);\n", // re-premultiply
         // PorterDuff
         "    fragColor = blendColors(colorBlend, fragColor);\n"
 };
diff --git a/libs/hwui/Renderer.h b/libs/hwui/Renderer.h
index 6d4bb4a..3681637 100644
--- a/libs/hwui/Renderer.h
+++ b/libs/hwui/Renderer.h
@@ -70,6 +70,7 @@ public:
     // TODO: move to a method on android:Paint
     static inline bool paintWillNotDraw(const SkPaint& paint) {
         return paint.getAlpha() == 0
+                && !paint.getColorFilter()
                 && getXfermode(paint.getXfermode()) != SkXfermode::kClear_Mode;
     }
 
@@ -77,6 +78,7 @@ public:
     static inline bool paintWillNotDrawText(const SkPaint& paint) {
         return paint.getAlpha() == 0
                 && paint.getLooper() == NULL
+                && !paint.getColorFilter()
                 && getXfermode(paint.getXfermode()) == SkXfermode::kSrcOver_Mode;
     }
 // ----------------------------------------------------------------------------