Analytic AntiAlias for Convex Shapes

src/core/SkBlitter.cpp

Index: src/core/SkBlitter.cpp
diff --git a/src/core/SkBlitter.cpp b/src/core/SkBlitter.cpp
index db9fcda93b19fc3b364859b0727de89e3b55888e..b57bd43ad0a4ebe7bd123a03f4afadda235e7f3e 100644
--- a/src/core/SkBlitter.cpp
+++ b/src/core/SkBlitter.cpp
@@ -71,17 +71,22 @@ void SkBlitter::blitRect(int x, int y, int width, int height) {
     }
 }
 
-/// Default implementation doesn't check for any easy optimizations
-/// such as alpha == 0 or 255; also uses blitV(), which some subclasses
+/// Default implementation doesn't check for easy optimizations
+/// such as alpha == 255; also uses blitV(), which some subclasses
 /// may not support.
 void SkBlitter::blitAntiRect(int x, int y, int width, int height,
                              SkAlpha leftAlpha, SkAlpha rightAlpha) {
-    this->blitV(x++, y, height, leftAlpha);
+    if (leftAlpha > 0) { // we may send in x = -1 with leftAlpha = 0

[reed1, 2016/08/18 20:31:00]

Can this land ahead of time, or does it only make sense w/ your CL?

[liyuqian, 2016/08/22 15:30:48]

I think it only make sens w/ my CL as previous algorithm won't have this edge
case.

+        this->blitV(x, y, height, leftAlpha);
+    }
+    x++;
     if (width > 0) {
         this->blitRect(x, y, width, height);
         x += width;
     }
-    this->blitV(x, y, height, rightAlpha);
+    if (rightAlpha > 0) {
+        this->blitV(x, y, height, rightAlpha);
+    }
 }
 
 //////////////////////////////////////////////////////////////////////////////