Add gm for displaying different variants of 8888.

src/core/SkBlitter_Sprite.cpp

 /*
  * 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.
  */
 
 #include "SkOpts.h"
 #include "SkSmallAllocator.h"
 #include "SkSpriteBlitter.h"
@@ skipping 131 matching lines @@
         special blitters regardless of these settings. Ignoring filtertype seems fine
         since by definition there is no scale in the matrix. Ignoring antialiasing is
         a bit of a hack, since we "could" pass in the fractional left/top for the bitmap,
         and respect that by blending the edges of the bitmap against the device. To support
         this we could either add more special blitters here, or detect antialiasing in the
         paint and return null if it is set, forcing the client to take the slow shader case
         (which does respect soft edges).
     */
     SkASSERT(allocator != nullptr);
 
+    // Defer to the general code if the pixels are unpremultipled. This case is not common,
+    // and this simplifies the code.
+    if (source.alphaType() == kUnpremul_SkAlphaType) {
+        return nullptr;
+    }
+
     SkSpriteBlitter* blitter = nullptr;
 
     if (SkSpriteBlitter_Src_SrcOver::Supports(dst, source, paint)) {
         blitter = allocator->createT<SkSpriteBlitter_Src_SrcOver>(source);
     } else {
         switch (dst.colorType()) {
             case kRGB_565_SkColorType:
                 blitter = SkSpriteBlitter::ChooseD16(source, paint, allocator);
                 break;
             case kN32_SkColorType:
                 if (dst.info().isSRGB()) {
                     blitter = SkSpriteBlitter::ChooseS32(source, paint, allocator);
                 } else {
                     blitter = SkSpriteBlitter::ChooseL32(source, paint, allocator);
                 }
                 break;
             case kRGBA_F16_SkColorType:
                 blitter = SkSpriteBlitter::ChooseF16(source, paint, allocator);
                 break;
             default:
                 break;
         }
     }
 
     if (blitter) {
         blitter->setup(dst, left, top, paint);
     }
     return blitter;
 }