Sk4px blit mask.

src/core/Sk4px.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef Sk4px_DEFINED
 #define Sk4px_DEFINED
 
@@ skipping 147 matching lines @@
                 fn(Load2(dst), Load2(src)).store2(dst);
                 dst += 2; src += 2; n -= 2;
             }
             if (n >= 1) {
                 fn(Load1(dst), Load1(src)).store1(dst);
             }
             break;
         }
     }
 
+    // As above, but with dst4' = fn(dst4, alpha4).
+    template <typename Fn, typename Dst>
+    static void MapDstAlpha(int n, Dst* dst, const SkAlpha* a, const Fn& fn) {
+        while (n > 0) {
+            if (n >= 8) {
+                Sk4px dst0 = fn(Load4(dst+0), Load4Alphas(a+0)),
+                      dst4 = fn(Load4(dst+4), Load4Alphas(a+4));
+                dst0.store4(dst+0);
+                dst4.store4(dst+4);
+                dst += 8; a += 8; n -= 8;
+                continue;  // Keep our stride at 8 pixels as long as possible.
+            }
+            SkASSERT(n <= 7);
+            if (n >= 4) {
+                fn(Load4(dst), Load4Alphas(a)).store4(dst);
+                dst += 4; a += 4; n -= 4;
+            }
+            if (n >= 2) {
+                fn(Load2(dst), Load2Alphas(a)).store2(dst);
+                dst += 2; a += 2; n -= 2;
+            }
+            if (n >= 1) {
+                fn(Load1(dst), DupAlpha(*a)).store1(dst);
+            }
+            break;
+        }
+    }
+
     // As above, but with dst4' = fn(dst4, src4, alpha4).
     template <typename Fn, typename Dst>
     static void MapDstSrcAlpha(int n, Dst* dst, const SkPMColor* src, const SkAlpha* a,
                                const Fn& fn) {
         while (n > 0) {
             if (n >= 8) {
                 Sk4px dst0 = fn(Load4(dst+0), Load4(src+0), Load4Alphas(a+0)),
                       dst4 = fn(Load4(dst+4), Load4(src+4), Load4Alphas(a+4));
                 dst0.store4(dst+0);
                 dst4.store4(dst+4);
@@ skipping 28 matching lines @@
     #if SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2
         #include "../opts/Sk4px_SSE2.h"
     #elif defined(SK_ARM_HAS_NEON)
         #include "../opts/Sk4px_NEON.h"
     #else
         #include "../opts/Sk4px_none.h"
     #endif
 #endif
 
 #endif//Sk4px_DEFINED