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
     };
 
     /*
+     * Used to define the input format of the bmp
+     */
+    enum BmpInputFormat {
+        kStandard_BmpInputFormat,
+        kRLE_BmpInputFormat,
+        kBitMask_BmpInputFormat,
+        kUnknown_BmpInputFormat
+    };
+
+    /*
      * 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);
+    SkBmpCodec(const SkImageInfo& info, SkStream* stream, BmpInputFormat inputFormat,
+            uint16_t bitsPerPixel, RowOrder 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 NULL, 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);
@@ skipping 32 matching lines @@
     RowOrder rowOrder() const { return fRowOrder; }
 
 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;
+    /*
+     * Allow to BmpCodec subclasses to implement unique onStart() functions

[scroggo, 2015/08/14 21:53:00]

Maybe mention that this relates to scanline decoding?

[msarett, 2015/08/17 19:16:13]

This is now shared with onGetPixels().

+     */
+    virtual SkCodec::Result onStart(const SkImageInfo& dstInfo, const SkCodec::Options& options,

[scroggo, 2015/08/14 21:53:01]

I do not know whether it's good or bad that this shares the same name as
SkScanlineDecoder::onStart.

Would it make sense for onGetPixels to call onStart?

[msarett, 2015/08/17 19:16:13]

I think it makes sense to change the name because it's a bit confusing to
duplicate the name of a scanline decoding function.  With the name change, I
think it makes sense to share this function with onGetPixels().

+            SkPMColor inputColorPtr[], int* inputColorCount) = 0;
+
+    /*
+     * Performs the row by row decode
+     * Unique for each of the bmp subclasses
+     */
+    virtual Result decode(const SkImageInfo& dstInfo, void* dst, size_t dstRowBytes,

[scroggo, 2015/08/14 21:53:01]

Can you add a description for these parameters? I think it's interesting (and
not necessarily intuitive) that the height of dstInfo allows the caller to do a
subset (of lines - not in X).

Also, I assume it decodes the next dstInfo.height() lines?

[msarett, 2015/08/17 19:16:13]

Yeah I'm adding comments, this is awkward.  Ideally we would share a decodeRow()
function and do away with this capability (since we are not enabling subsets for
bmp).

decodeRow() isn't a good fit for RLE though.  So I think sticking with decode()
is the best design move.

+            const Options& opts) = 0;
+
+    const BmpInputFormat fInputFormat;
+    const uint16_t       fBitsPerPixel;
+    const RowOrder       fRowOrder;
+
+    friend class SkBmpScanlineDecoder;
 
     typedef SkCodec INHERITED;
 };
 
 #endif