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 "SkStream.h"
+#include "SkSwizzler.h"
+#include "SkTypes.h"
+
+#ifdef SK_SUPPORT_LEGACY_IMAGE_GENERATOR_RETURN

[scroggo, 2015/03/04 17:10:30]

No longer needed

+    #define onGetPixels onGetPixelsEnum
+#endif
+
+/*
+ *
+ * This class implements the decoding for bmp images
+ *
+ */
+class SkBmpCodec : public SkCodec {
+public:
+
+    /*
+     *
+     * 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
+    };
+
+    /*
+     *
+     * 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 standard and bit masks input format
+     *
+     */
+    Result decode(const SkImageInfo& dstInfo, void* dst, uint32_t dstRowBytes);
+
+    /*
+     *
+     * Performs the bitmap decoding for RLE input format
+     *
+     */
+    Result decodeRLE(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
+                        passes ownership to SkBmpCodec

[scroggo, 2015/03/04 17:10:30]

no longer true.

+     * @param colorTable color table for index-based bmp formats

[scroggo, 2015/03/04 17:10:30]

nit: Maybe it's obvious, but this doesn't mention that it's an array?

+     *                  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,
+               SkSwizzler::ColorMasks bitMasks, SkPMColor* colorTable,
+               SkSwizzler::RowOrder rowOrder, uint32_t remainingBytes);
+
+    // Fields
+    const uint16_t                              fBitsPerPixel;
+    const BitmapInputFormat                     fInputFormat;
+    const SkSwizzler::ColorMasks                fBitMasks;
+    const SkAutoTDeleteArray<SkPMColor>         fColorTable;   // owned
+    const SkSwizzler::RowOrder                  fRowOrder;
+    const uint32_t                              fRemainingBytes;
+
+    typedef SkCodec INHERITED;
+};