Pass compressed blitters to our mask drawing algorithm

src/utils/SkTextureCompressor_ASTC.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkTextureCompressor_ASTC.h"
 #include "SkTextureCompressor_Blitter.h"
 
@@ skipping 1993 matching lines @@
     uint8_t** dstPtr = &dst;
     for (int y = 0; y < height; y += 12) {
         for (int x = 0; x < width; x += 12) {
             compress_a8_astc_block<GetAlpha>(dstPtr, src + y*rowBytes + x, rowBytes);
         }
     }
 
     return true;
 }
 
-SkBlitter* CreateASTCBlitter(int width, int height, void* outputBuffer) {
-    return new
-        SkTCompressedAlphaBlitter<12, 16, CompressA8ASTCBlockVertical>
+SkBlitter* CreateASTCBlitter(int width, int height, void* outputBuffer,
+                             SkTBlitterAllocator* allocator) {
+    if ((width % 12) != 0 || (height % 12) != 0) {
+        return NULL;
+    }
+
+    // Memset the output buffer to an encoding that decodes to zero. We must do this
+    // in order to avoid having uninitialized values in the buffer if the blitter
+    // decides not to write certain scanlines (and skip entire rows of blocks).
+    // In the case of ASTC, if everything index is zero, then the interpolated value
+    // will decode to zero provided we have the right header. We use the encoding
+    // from recognizing all zero blocks from above.
+    const int nBlocks = (width * height / 144);
+    uint8_t *dst = reinterpret_cast<uint8_t *>(outputBuffer);
+    for (int i = 0; i < nBlocks; ++i) {
+        send_packing(&dst, SkTEndian_SwapLE64(0x0000000001FE000173ULL), 0);
+    }
+
+    return allocator->createT<
+        SkTCompressedAlphaBlitter<12, 16, CompressA8ASTCBlockVertical>, int, int, void* >
         (width, height, outputBuffer);
 }
 
 void DecompressASTC(uint8_t* dst, int dstRowBytes, const uint8_t* src,
                     int width, int height, int blockDimX, int blockDimY) {
     // ASTC is encoded in what they call "raster order", so that the first
     // block is the bottom-left block in the image, and the first pixel
     // is the bottom-left pixel of the image
     dst += height * dstRowBytes;
 
     ASTCDecompressionData data(blockDimX, blockDimY);
     for (int y = 0; y < height; y += blockDimY) {
         dst -= blockDimY * dstRowBytes;
         SkColor *colorPtr = reinterpret_cast<SkColor*>(dst);
         for (int x = 0; x < width; x += blockDimX) {
             read_astc_block(&data, src);
             decompress_astc_block(reinterpret_cast<uint8_t*>(colorPtr + x), dstRowBytes, data);
 
             // ASTC encoded blocks are 16 bytes (128 bits) large.
             src += 16;
         }
     }
 }
 
 }  // SkTextureCompressor