Analytic AntiAlias for Convex Shapes

src/core/SkAntiRun.h

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef SkAntiRun_DEFINED
 #define SkAntiRun_DEFINED
@@ skipping 61 matching lines @@
             x = 0;
             SkDEBUGCODE(this->validate();)
         }
 
         if (middleCount) {
             SkAlphaRuns::Break(runs, alpha, x, middleCount);
             alpha += x;
             runs += x;
             x = 0;
             do {
-                alpha[0] = SkToU8(alpha[0] + maxValue);
+                alpha[0] = SkToU8(SkTMin<int>(0xFF, alpha[0] + maxValue));

[caryclark, 2016/08/10 13:08:09]

In what case is this needed?

[liyuqian, 2016/08/16 13:22:05]

Our RunBaseAdditiveBlitter uses SkAntiRun and it may trigger this case when
we're adding alphas of two partial rows.

                 int n = runs[0];
                 SkASSERT(n <= middleCount);
                 alpha += n;
                 runs += n;
                 middleCount -= n;
             } while (middleCount > 0);
             SkDEBUGCODE(this->validate();)
             lastAlpha = alpha;
         }
 
@@ skipping 88 matching lines @@
             x -= n;
         }
     }
 
 private:
     SkDEBUGCODE(int fWidth;)
     SkDEBUGCODE(void validate() const;)
 };
 
 #endif