Pass compressed blitters to our mask drawing algorithm

src/utils/SkTextureCompressor_LATC.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_LATC.h"
 #include "SkTextureCompressor_Blitter.h"
 
+#include "SkBlitter.h"
 #include "SkEndian.h"
 
 // Compression options. In general, the slow version is much more accurate, but
 // much slower. The fast option is much faster, but much less accurate. YMMV.
 #define COMPRESS_LATC_SLOW 0
 #define COMPRESS_LATC_FAST 1
 
 ////////////////////////////////////////////////////////////////////////////////
 
 // Generates an LATC palette. LATC constructs
@@ skipping 399 matching lines @@
 bool CompressA8ToLATC(uint8_t* dst, const uint8_t* src, int width, int height, int rowBytes) {
 #if COMPRESS_LATC_FAST
     return compress_4x4_a8_latc(dst, src, width, height, rowBytes);
 #elif COMPRESS_LATC_SLOW
     return compress_4x4_a8_to_64bit(dst, src, width, height, rowBytes, compress_latc_block);
 #else
 #error "Must choose either fast or slow LATC compression"
 #endif
 }
 
-SkBlitter* CreateLATCBlitter(int width, int height, void* outputBuffer) {
+SkBlitter* CreateLATCBlitter(int width, int height, void* outputBuffer,
+                             SkTBlitterAllocator* allocator) {
+    if ((width % 4) != 0 || (height % 4) != 0) {
+        return NULL;
+    }
+
 #if COMPRESS_LATC_FAST
-    return new
-        SkTCompressedAlphaBlitter<4, 8, CompressA8LATCBlockVertical>
+    // 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 LATC, if everything is zero, then LUM0 and LUM1 are also zero,
+    // and they will only be non-zero (0xFF) if the index is 7. So bzero will do just fine.
+    // (8 bytes per block) * (w * h / 16 blocks) = w * h / 2
+    sk_bzero(outputBuffer, width * height / 2);
+
+    return allocator->createT<
+        SkTCompressedAlphaBlitter<4, 8, CompressA8LATCBlockVertical>, int, int, void* >
         (width, height, outputBuffer);
 #elif COMPRESS_LATC_SLOW
     // TODO (krajcevski)
     return NULL;
 #endif
 }
 
 void DecompressLATC(uint8_t* dst, int dstRowBytes, const uint8_t* src, int width, int height) {
     for (int j = 0; j < height; j += 4) {
         for (int i = 0; i < width; i += 4) {
             decompress_latc_block(dst + i, dstRowBytes, src);
             src += 8;
         }
         dst += 4 * dstRowBytes;
     }
 }
 
 }  // SkTextureCompressor