Scanline decoding for bmp

src/codec/SkBmpCodec.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.
  */
 #ifndef SkBmpCodec_DEFINED
 #define SkBmpCodec_DEFINED
 
 #include "SkCodec.h"
 #include "SkColorTable.h"
 #include "SkImageInfo.h"
 #include "SkMaskSwizzler.h"
+#include "SkScanlineDecoder.h"
 #include "SkStream.h"
 #include "SkSwizzler.h"
 #include "SkTypes.h"
 
 /*
  * This class enables code sharing between its bmp codec subclasses.  The
  * subclasses actually do the work.
  */
 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 bmp
      */
     static bool IsBmp(SkStream*);
 
     /*
      * Assumes IsBmp was called and returned true
      * Creates a bmp decoder
      * Reads enough of the stream to determine the image format
      */
     static SkCodec* NewFromStream(SkStream*);
 
     /*
      * Creates a bmp decoder for a bmp embedded in ico
      * Reads enough of the stream to determine the image format
      */
     static SkCodec* NewFromIco(SkStream*);
 
+    /*
+     * Assumes IsBmp was called and returned true
+     * Creates a bmp scanline decoder
+     * Takes ownership of the stream
+     */
+    static SkScanlineDecoder* NewSDFromStream(SkStream* stream);
+
 protected:
 
     SkBmpCodec(const SkImageInfo& info, SkStream* stream, uint16_t bitsPerPixel,
-            RowOrder rowOrder);
+            SkScanlineDecoder::SkScanlineOrder rowOrder);
 
     SkEncodedFormat onGetEncodedFormat() const override { return kBMP_SkEncodedFormat; }
 
     /*
      * Read enough of the stream to initialize the SkBmpCodec. Returns a bool
      * representing success or failure. If it returned true, and codecOut was
      * not nullptr, it will be set to a new SkBmpCodec.
      * Does *not* take ownership of the passed in SkStream.
      */
     static bool ReadHeader(SkStream*, bool inIco, SkCodec** codecOut);
 
     bool onRewind() override;
 
     /*
      * Returns whether this BMP is part of an ICO image.
      */
     bool inIco() const {
         return this->onInIco();
     }
 
     virtual bool onInIco() const {
         return false;
     }
 
     /*
+     * Get the destination row number corresponding to the encoded row number.
+     * For kTopDown, we simply return y, but for kBottomUp, the rows will be
+     * decoded in reverse order.
+     *
+     * @param y      Iterates from 0 to height, indicating the current row.
+     * @param height The height of the current subset of the image that we are
+     *               decoding.  This is generally equal to the full height
+     *               when we want to decode the full or one when we are
+     *               sampling.
+     */
+    int32_t getDstRow(int32_t y, int32_t height);
+
+    /*
      * Get the destination row to start filling from
      * Used to fill the remainder of the image on incomplete input for bmps
      * This is tricky since bmps may be kTopDown or kBottomUp.  For kTopDown,
      * we start filling from where we left off, but for kBottomUp we start
      * filling at the top of the image.
      */
     void* getDstStartRow(void* dst, size_t dstRowBytes, int32_t y) const;
 
     /*
      * Compute the number of colors in the color table
      */
     uint32_t computeNumColors(uint32_t numColors);
 
     /*
      * Accessors used by subclasses
      */
     uint16_t bitsPerPixel() const { return fBitsPerPixel; }
-    RowOrder rowOrder() const { return fRowOrder; }
+    SkScanlineDecoder::SkScanlineOrder rowOrder() const { return fRowOrder; }
+
+    /*
+     * To be overriden by bmp subclasses, which provide unique implementations.
+     * Performs subclass specific setup.
+     *
+     * @param dstInfo         Contains output information.  Height specifies
+     *                        the total number of rows that will be decoded.
+     * @param options         Additonal options to pass to the decoder.
+     * @param inputColorPtr   Client-provided memory for a color table.  Must
+     *                        be enough for 256 colors.  This will be
+     *                        populated with colors if the encoded image uses
+     *                        a color table.
+     * @param inputColorCount If the encoded image uses a color table, this
+     *                        will be set to the number of colors in the
+     *                        color table.
+     */
+    virtual SkCodec::Result prepareToDecode(const SkImageInfo& dstInfo,
+            const SkCodec::Options& options, SkPMColor inputColorPtr[],
+            int* inputColorCount) = 0;
 
 private:
 
     /*
      * Creates a bmp decoder
      * Reads enough of the stream to determine the image format
      */
     static SkCodec* NewFromStream(SkStream*, bool inIco);
 
-    const uint16_t fBitsPerPixel;
-    const RowOrder fRowOrder;
+    /*
+     * Decodes the next dstInfo.height() lines.
+     *
+     * onGetPixels() uses this for full image decodes.
+     * SkScaledCodec::onGetPixels() uses the scanline decoder to call this with
+     * dstInfo.height() = 1, in order to implement sampling.
+     * A potential future use is to allow the caller to decode a subset of the
+     * lines in the image.
+     *
+     * @param dstInfo     Contains output information.  Height specifies the
+     *                    number of rows to decode at this time.
+     * @param dst         Memory location to store output pixels
+     * @param dstRowBytes Bytes in a row of the destination
+     */
+    virtual Result decodeRows(const SkImageInfo& dstInfo, void* dst, size_t dstRowBytes,
+            const Options& opts) = 0;
+
+    const uint16_t                           fBitsPerPixel;
+    const SkScanlineDecoder::SkScanlineOrder fRowOrder;
+
+    friend class SkBmpScanlineDecoder;
 
     typedef SkCodec INHERITED;
 };
 
 #endif