Allow sampling GIF images during decode.

src/images/SkScaledBitmapSampler.h

 
 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #ifndef SkScaledBitmapSampler_DEFINED
 #define SkScaledBitmapSampler_DEFINED
 
 #include "SkTypes.h"
 #include "SkColor.h"
 #include "SkImageDecoder.h"
 
 class SkBitmap;
 
 class SkScaledBitmapSampler {
 public:
     SkScaledBitmapSampler(int origWidth, int origHeight, int cellSize);
 
     int scaledWidth() const { return fScaledWidth; }
     int scaledHeight() const { return fScaledHeight; }
 
     int srcY0() const { return fY0; }
+    int srcDX() const { return fDX; }
     int srcDY() const { return fDY; }
 
     enum SrcConfig {
         kGray,  // 1 byte per pixel
         kIndex, // 1 byte per pixel
         kRGB,   // 3 bytes per pixel
         kRGBX,  // 4 byes per pixel (ignore 4th)
         kRGBA,  // 4 bytes per pixel
         kRGB_565 // 2 bytes per pixel
     };
 
     // Given a dst bitmap (with pixels already allocated) and a src-config,
     // prepares iterator to process the src colors and write them into dst.
     // Returns false if the request cannot be fulfulled.
     bool begin(SkBitmap* dst, SrcConfig sc, const SkImageDecoder& decoder,
                const SkPMColor* = NULL);
     // call with row of src pixels, for y = 0...scaledHeight-1.
     // returns true if the row had non-opaque alpha in it
     bool next(const uint8_t* SK_RESTRICT src);
 
+    // Like next(), but specifies the y value of the source row, so the
+    // rows can come in any order. If the row is not part of the output
+    // sample, it will be skipped. Only sampleInterlaced OR next should
+    // be called for one SkScaledBitmapSampler.
+    bool sampleInterlaced(const uint8_t* SK_RESTRICT src, int srcY);
+
     typedef bool (*RowProc)(void* SK_RESTRICT dstRow,
                             const uint8_t* SK_RESTRICT src,
                             int width, int deltaSrc, int y,
                             const SkPMColor[]);
 
 private:
     int fScaledWidth;
     int fScaledHeight;
 
     int fX0;    // first X coord to sample
     int fY0;    // first Y coord (scanline) to sample
     int fDX;    // step between X samples
     int fDY;    // step between Y samples
 
+#ifdef SK_DEBUG
+    // Keep track of whether the caller is using next or sampleInterlaced.
+    // Only one can be used per sampler.
+    enum SampleMode {
+        kUninitialized_SampleMode,
+        kConsecutive_SampleMode,
+        kInterlaced_SampleMode,
+    };
+
+    SampleMode fSampleMode;
+#endif
+
     // setup state
     char*   fDstRow; // points into bitmap's pixels
     size_t  fDstRowBytes;
     int     fCurrY; // used for dithering
     int     fSrcPixelSize;  // 1, 3, 4
     RowProc fRowProc;
 
     // optional reference to the src colors if the src is a palette model
     const SkPMColor* fCTable;
 
 #ifdef SK_DEBUG
     // Helper class allowing a test to have access to fRowProc.
     friend class RowProcTester;
 #endif
 };
 
 #endif