Correctly implement the CLEAR xfermode.

The previous implementation was using glBlendFunc with the parameters
GL_ZERO/GL_ZERO which doesn't work for text, paths and other alpha
sources (anti-aliasing.) The correct implementation is GL_ZERO/
GL_ONE_MINUS_SRC_ALPHA.

Change-Id: I4cca65e57b6a37bbf5a41d382cb0648ee8e11e79

4 files changed, 38 insertions, 6 deletions

diff --git a/libs/hwui/Debug.h b/libs/hwui/Debug.h
index f74238e..2cdc8c3 100644
--- a/libs/hwui/Debug.h
+++ b/libs/hwui/Debug.h
@@ -37,6 +37,8 @@
 
 // Turn on to display debug info about 9patch objects
 #define DEBUG_PATCHES 0
+// Turn on to "explode" 9patch objects
+#define DEBUG_EXPLODE_PATCHES 0
 // Turn on to display vertex and tex coords data about 9patch objects
 // This flag requires DEBUG_PATCHES to be turned on
 #define DEBUG_PATCHES_VERTICES 0
diff --git a/libs/hwui/OpenGLRenderer.cpp b/libs/hwui/OpenGLRenderer.cpp
index 560c1f9..8cf325b 100644
--- a/libs/hwui/OpenGLRenderer.cpp
+++ b/libs/hwui/OpenGLRenderer.cpp
@@ -63,7 +63,7 @@ struct Blender {
 // In this array, the index of each Blender equals the value of the first
 // entry. For instance, gBlends[1] == gBlends[SkXfermode::kSrc_Mode]
 static const Blender gBlends[] = {
-    { SkXfermode::kClear_Mode,   GL_ZERO,                 GL_ZERO },
+    { SkXfermode::kClear_Mode,   GL_ZERO,                 GL_ONE_MINUS_SRC_ALPHA },
     { SkXfermode::kSrc_Mode,     GL_ONE,                  GL_ZERO },
     { SkXfermode::kDst_Mode,     GL_ZERO,                 GL_ONE },
     { SkXfermode::kSrcOver_Mode, GL_ONE,                  GL_ONE_MINUS_SRC_ALPHA },
@@ -81,7 +81,7 @@ static const Blender gBlends[] = {
 // this array's SrcOver blending mode is actually DstOver. You can refer to
 // createLayer() for more information on the purpose of this array.
 static const Blender gBlendsSwap[] = {
-    { SkXfermode::kClear_Mode,   GL_ZERO,                 GL_ZERO },
+    { SkXfermode::kClear_Mode,   GL_ONE_MINUS_DST_ALPHA,  GL_ZERO },
     { SkXfermode::kSrc_Mode,     GL_ZERO,                 GL_ONE },
     { SkXfermode::kDst_Mode,     GL_ONE,                  GL_ZERO },
     { SkXfermode::kSrcOver_Mode, GL_ONE_MINUS_DST_ALPHA,  GL_ONE },
diff --git a/libs/hwui/Patch.cpp b/libs/hwui/Patch.cpp
index 11eb953..f7dacae 100644
--- a/libs/hwui/Patch.cpp
+++ b/libs/hwui/Patch.cpp
@@ -152,12 +152,12 @@ void Patch::updateVertices(const float bitmapWidth, const float bitmapHeight,
     float previousStepY = 0.0f;
 
     float y1 = 0.0f;
+    float y2 = 0.0f;
     float v1 = 0.0f;
 
     for (uint32_t i = 0; i < mYCount; i++) {
         float stepY = mYDivs[i];
 
-        float y2 = 0.0f;
         if (i & 1) {
             const float segment = stepY - previousStepY;
             y2 = y1 + floorf(segment * stretchY + 0.5f);
@@ -167,8 +167,15 @@ void Patch::updateVertices(const float bitmapWidth, const float bitmapHeight,
         float v2 = fmax(0.0f, stepY - 0.5f) / bitmapHeight;
 
         if (stepY > 0.0f) {
+#if DEBUG_EXPLODE_PATCHES
+            y1 += i * EXPLODE_GAP;
+            y2 += i * EXPLODE_GAP;
+#endif
             generateRow(vertex, y1, y2, v1, v2, stretchX, right - left,
                     bitmapWidth, quadCount);
+#if DEBUG_EXPLODE_PATCHES
+            y2 -= i * EXPLODE_GAP;
+#endif
         }
 
         y1 = y2;
@@ -178,7 +185,12 @@ void Patch::updateVertices(const float bitmapWidth, const float bitmapHeight,
     }
 
     if (previousStepY != bitmapHeight) {
-        generateRow(vertex, y1, bottom - top, v1, 1.0f, stretchX, right - left,
+        y2 = bottom - top;
+#if DEBUG_EXPLODE_PATCHES
+        y1 += mYCount * EXPLODE_GAP;
+        y2 += mYCount * EXPLODE_GAP;
+#endif
+        generateRow(vertex, y1, y2, v1, 1.0f, stretchX, right - left,
                 bitmapWidth, quadCount);
     }
 
@@ -202,13 +214,13 @@ void Patch::generateRow(TextureVertex*& vertex, float y1, float y2, float v1, fl
     float previousStepX = 0.0f;
 
     float x1 = 0.0f;
+    float x2 = 0.0f;
     float u1 = 0.0f;
 
     // Generate the row quad by quad
     for (uint32_t i = 0; i < mXCount; i++) {
         float stepX = mXDivs[i];
 
-        float x2 = 0.0f;
         if (i & 1) {
             const float segment = stepX - previousStepX;
             x2 = x1 + floorf(segment * stretchX + 0.5f);
@@ -218,7 +230,14 @@ void Patch::generateRow(TextureVertex*& vertex, float y1, float y2, float v1, fl
         float u2 = fmax(0.0f, stepX - 0.5f) / bitmapWidth;
 
         if (stepX > 0.0f) {
+#if DEBUG_EXPLODE_PATCHES
+            x1 += i * EXPLODE_GAP;
+            x2 += i * EXPLODE_GAP;
+#endif
             generateQuad(vertex, x1, y1, x2, y2, u1, v1, u2, v2, quadCount);
+#if DEBUG_EXPLODE_PATCHES
+            x2 -= i * EXPLODE_GAP;
+#endif
         }
 
         x1 = x2;
@@ -228,7 +247,12 @@ void Patch::generateRow(TextureVertex*& vertex, float y1, float y2, float v1, fl
     }
 
     if (previousStepX != bitmapWidth) {
-        generateQuad(vertex, x1, y1, width, y2, u1, v1, 1.0f, v2, quadCount);
+        x2 = width;
+#if DEBUG_EXPLODE_PATCHES
+        x1 += mXCount * EXPLODE_GAP;
+        x2 += mXCount * EXPLODE_GAP;
+#endif
+        generateQuad(vertex, x1, y1, x2, y2, u1, v1, 1.0f, v2, quadCount);
     }
 }
 
diff --git a/libs/hwui/Patch.h b/libs/hwui/Patch.h
index 0f0ffa2..28c9048 100644
--- a/libs/hwui/Patch.h
+++ b/libs/hwui/Patch.h
@@ -31,6 +31,12 @@ namespace android {
 namespace uirenderer {
 
 ///////////////////////////////////////////////////////////////////////////////
+// Defines
+///////////////////////////////////////////////////////////////////////////////
+
+#define EXPLODE_GAP 4
+
+///////////////////////////////////////////////////////////////////////////////
 // 9-patch structures
 ///////////////////////////////////////////////////////////////////////////////