Split SkBmpCodec into three separate classes

src/codec/SkBmpRLECodec.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.
+ */
+
+#include "SkBmpCodec.h"
+#include "SkColorTable.h"
+#include "SkImageInfo.h"
+#include "SkTypes.h"
+
+/*
+ * This class implements the decoding for bmp images that use an RLE encoding
+ */
+class SkBmpRLECodec : public SkBmpCodec {
+public:
+
+    /*
+     * Creates an instance of the decoder
+     * Called only by SkBmpCodec::NewFromStream

[scroggo, 2015/08/04 16:16:46]

Interesting that you say that, because it is a public method.

It is in src/ so maybe that plus the comment is enough to dissuade someone from
trying to call it directly.

I suppose you could make SkBmpCodec a friend of SkBmpRLECodec, so this
constructor could be private, but that seems weird?

[msarett, 2015/08/04 23:14:45]

Yeah I'm pretty happy with the subclasses instead of friend classes design. 
Public constructors on the subclasses is the main drawback.  I will make the
comment a little stronger to hopefully dissuade anyone from calling it.

+     *
+     * @param srcInfo contains the source width and height
+     * @param stream the stream of image data

[scroggo, 2015/08/04 16:16:46]

nit: encoded (image data)

[msarett, 2015/08/04 23:14:45]

Done.

+     * @param bitsPerPixel the number of bits used to store each pixel
+     * @param numColors the number of colors in the color table
+     * @param bytesPerColor the number of bytes in the stream used to represent
+                            each color in the color table
+     * @param offset the offset of the image pixel data from the end of the
+     *               headers
+     * @param rowOrder indicates whether rows are ordered top-down or bottom-up
+     * @param RLEBytes used only for RLE decodes, as we must decode all

[scroggo, 2015/08/04 16:16:46]

It seems redundant to say this is used only for RLE decodes, since this class is
only for decoding RLE

[msarett, 2015/08/04 23:14:45]

Done.

+     *                  of the data at once rather than row by row
+     *                  it indicates the amount of data left in the stream
+     *                  after decoding the headers
+     */
+    SkBmpRLECodec(const SkImageInfo& srcInfo, SkStream* stream,
+                  uint16_t bitsPerPixel, uint32_t numColors,
+                  uint32_t bytesPerColor, uint32_t offset,
+                  SkBmpCodec::RowOrder rowOrder, size_t RLEBytes);
+
+protected:
+
+    Result onGetPixels(const SkImageInfo& dstInfo, void* dst,
+                       size_t dstRowBytes, const Options&, SkPMColor*,
+                       int*) override;
+
+private:
+
+    /*
+     * Creates the color table
+     * Sets colorCount to the new color count if it is non-NULL
+     */
+    bool createColorTable(SkAlphaType alphaType, int* colorCount);

[msarett, 2015/08/03 22:52:36]

Used to be in SkBmpCodec.  This has been simplified given that we know we are
creating a color table for RLE mode (fIsIco is always false, alpha is always
0xFF).

+
+    bool initializeStreamBuffer();

[msarett, 2015/08/03 22:52:36]

Factored out of decodeRLE().  Will make scanline decoding easier.

+
+    /*
+     * Set an RLE pixel using the color table
+     */
+    void setPixel(void* dst, size_t dstRowBytes,
+                  const SkImageInfo& dstInfo, uint32_t x, uint32_t y,
+                  uint8_t index);
+    /*
+     * Set an RLE24 pixel from R, G, B values
+     */
+    void setRGBPixel(void* dst, size_t dstRowBytes,
+                     const SkImageInfo& dstInfo, uint32_t x, uint32_t y,
+                     uint8_t red, uint8_t green, uint8_t blue);
+
+    /*
+     * Performs the bitmap decoding for RLE input format
+     */
+    Result decode(const SkImageInfo& dstInfo, void* dst,

[msarett, 2015/08/03 22:52:36]

Used to be decodeRLE() in SkBmpCodec.

+                  size_t dstRowBytes, const Options& opts);
+
+    SkAutoTUnref<SkColorTable>          fColorTable;    // owned
+    uint32_t                            fNumColors;
+    const uint32_t                      fBytesPerColor;
+    const uint32_t                      fOffset;
+    SkAutoTDeleteArray<uint8_t>         fStreamBuffer;
+    size_t                              fRLEBytes;
+    uint32_t                            fCurrRLEByte;
+
+    typedef SkBmpCodec INHERITED;
+};