Bmp Image Decoding

src/codec/SkCodec_libbmp.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 "SkCodec.h"
+#include "SkImageInfo.h"
+#include "SkMaskSwizzler.h"
+#include "SkStream.h"
+#include "SkSwizzler.h"
+#include "SkTypes.h"
+
+// TODO: rename SkCodec_libbmp files to SkBmpCodec
+// TODO: define a wrapper for SkDebugf that doesn't always print
+/*
+ *
+ * This class implements the decoding for bmp images
+ *
+ */
+class SkBmpCodec : public SkCodec {
+public:
+
+    /*
+     *
+     * Describes if rows of the input start at the top or bottom of the image
+     *
+     */
+    enum RowOrder {
+        kTopDown_RowOrder,
+        kBottomUp_RowOrder
+    };
+
+    /*
+     *
+     * Checks the start of the stream to see if the image is a bitmap
+     *
+     */
+    static bool IsBmp(SkStream*);
+
+    /*
+     *
+     * Assumes IsBmp was called and returned true
+     * Creates a bitmap decoder
+     * Reads enough of the stream to determine the image format
+     *
+     */
+    static SkCodec* NewFromStream(SkStream*);
+
+protected:
+
+    /*
+     *
+     * Initiates the bitmap decode
+     *
+     */
+    virtual Result onGetPixels(const SkImageInfo& dstInfo, void* dst,
+                               size_t dstRowBytes, SkPMColor*,
+                               int*) SK_OVERRIDE;
+
+private:
+
+    /*
+     *
+     * Used to define the input format of the bitmap
+     *
+     */
+    enum BitmapInputFormat {
+        kStandard_BitmapInputFormat,
+        kRLE_BitmapInputFormat,
+        kBitMask_BitmapInputFormat,
+        kUnknown_BitmapInputFormat
+    };
+
+    /*
+     *
+     * Performs the bitmap decoding for bit masks input format
+     *
+     */
+    Result decodeMask(const SkImageInfo& dstInfo, void* dst,
+                      uint32_t dstRowBytes);
+
+    /*
+     *
+     * Set an RLE pixel using the color table
+     *
+     */
+    void setRLEPixel(SkPMColor* dst, uint32_t dstRowBytes, int height,
+                     uint32_t x, uint32_t y, uint8_t index);
+
+    /*
+     *
+     * Performs the bitmap decoding for RLE input format
+     *
+     */
+    Result decodeRLE(const SkImageInfo& dstInfo, void* dst,
+                     uint32_t dstRowBytes);
+
+    /*
+     *
+     * Performs the bitmap decoding for standard input format
+     *
+     */
+    Result decode(const SkImageInfo& dstInfo, void* dst, uint32_t dstRowBytes);
+
+    /*
+     *
+     * Creates an instance of the decoder
+     * Called only by NewFromStream
+     *
+     * @param srcInfo contains the source width and height
+     * @param stream the stream of image data
+     * @param bitsPerPixel the number of bits used to store each pixel
+     * @param format the format of the bmp file
+     * @param bitMasks optional color masks for certain bmp formats

[scroggo, 2015/03/11 19:22:45]

masks*

Also, can you add a comment about ownership? It looks like we currently leak
masks.

[msarett, 2015/03/11 20:03:11]

You are correct.  I made fMasks an AutoTDelete and designed the pointer as owned
by SkBmpCodec.

+     * @param colorTable array representing the color table for index-based bmp
+     *                   formats, passes ownership to SkBmpCodec
+     * @param rowOrder indicates whether rows are ordered top-down or bottom-up
+     * @param remainingBytes used only for RLE decodes, as we must decode all
+     *                  of the data at once rather than row by row
+     *                  it indicates the amount of data left in the stream
+     *                  after decoding the headers
+     *
+     */
+    SkBmpCodec(const SkImageInfo& srcInfo, SkStream* stream,
+               uint16_t bitsPerPixel, BitmapInputFormat format,
+               SkMasks* masks, SkPMColor* colorTable,
+               RowOrder rowOrder, uint32_t remainingBytes);
+
+    // Fields
+    const uint16_t                      fBitsPerPixel;
+    const BitmapInputFormat             fInputFormat;
+    SkMasks*                            fMasks;
+    const SkAutoTDeleteArray<SkPMColor> fColorTable;     // owned
+    const RowOrder                      fRowOrder;
+    const uint32_t                      fRemainingBytes;
+
+    typedef SkCodec INHERITED;
+};