Add ETC1 format to SkTextureCompressor

src/utils/SkTextureCompressor.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkTextureCompressor_DEFINED
 #define SkTextureCompressor_DEFINED
 
 #include "SkImageInfo.h"
 #include "SkBlitter.h"
 
 class SkBitmap;
 class SkData;
 
 namespace SkTextureCompressor {
     // Various texture compression formats that we support.
     enum Format {
         // Alpha only formats.
-        kLATC_Format,       // 4x4 blocks, compresses A8
-        kR11_EAC_Format,    // 4x4 blocks, compresses A8
-        kASTC_12x12_Format, // 12x12 blocks, compresses A8
+        kLATC_Format,       // 4x4 blocks, (de)compresses A8
+        kR11_EAC_Format,    // 4x4 blocks, (de)compresses A8
+
+        // RGB only formats
+        kETC1_Format,       // 4x4 blocks, compresses RGB 565, decompresses 8-bit RGB
+                            //    NOTE: ETC1 supports 8-bit RGB compression, but we
+                            //    currently don't have any RGB8 SkColorTypes. We could
+                            //    support 8-bit RGBA but we would have to preprocess the
+                            //    bitmap to insert alphas.
+
+        // Multi-purpose formats
+        kASTC_12x12_Format, // 12x12 blocks, compresses A8, decompresses RGBA
 
         kLast_Format = kASTC_12x12_Format
     };
     static const int kFormatCnt = kLast_Format + 1;
 
     // Returns the size of the compressed data given the width, height, and
     // desired compression format. If the width and height are not an appropriate
     // multiple of the block size, then this function returns an error (-1).
     int GetCompressedDataSize(Format fmt, int width, int height);
 
     // Returns an SkData holding a blob of compressed data that corresponds
     // to the bitmap. If the bitmap colorType cannot be compressed using the 
     // associated format, then we return NULL. The caller is responsible for
     // calling unref() on the returned data.
     SkData* CompressBitmapToFormat(const SkBitmap& bitmap, Format format);
 
     // Compresses the given src data into dst. The src data is assumed to be
     // large enough to hold width*height pixels. The dst data is expected to
     // be large enough to hold the compressed data according to the format.
     bool CompressBufferToFormat(uint8_t* dst, const uint8_t* src, SkColorType srcColorType,
                                 int width, int height, int rowBytes, Format format,
                                 bool opt = true /* Use optimization if available */);
 
     // Decompresses the given src data from the format specified into the
     // destination buffer. The width and height of the data passed corresponds
     // to the width and height of the uncompressed image. The destination buffer (dst)
     // is assumed to be large enough to hold the entire decompressed image. The
-    // decompressed image colors are determined based on the passed format:
-    //
-    // LATC -> Alpha 8
-    // R11_EAC -> Alpha 8
-    // ASTC -> RGBA
+    // decompressed image colors are determined based on the passed format.
     //
     // Note, CompressBufferToFormat compresses A8 data into ASTC. However,
     // general ASTC data encodes RGBA data, so that is what the decompressor
     // operates on.
     //
     // Returns true if successfully decompresses the src data.
     bool DecompressBufferFromFormat(uint8_t* dst, int dstRowBytes, const uint8_t* src,
                                     int width, int height, Format format);
 
     // This typedef defines what the nominal aspects of a compression function
@@ skipping 11 matching lines @@
     // Returns the desired dimensions of the block size for the given format. These dimensions
     // don't necessarily correspond to the specification's dimensions, since there may
     // be specialized algorithms that operate on multiple blocks at once. If the
     // flag 'matchSpec' is true, then the actual dimensions from the specification are
     // returned. If the flag is false, then these dimensions reflect the appropriate operable
     // dimensions of the compression functions.
     void GetBlockDimensions(Format format, int* dimX, int* dimY, bool matchSpec = false);
 }
 
 #endif