Bmp Image Decoding

src/codec/SkSwizzler.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 SkSwizzler_DEFINED
 #define SkSwizzler_DEFINED
 
 #include "SkTypes.h"
 #include "SkColor.h"
 #include "SkImageInfo.h"
 
 class SkSwizzler : public SkNoncopyable {
 public:
     /**
      *  Enum describing the config of the source data.
      */
     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
+        kGray,
+        kIndex1,
+        kIndex2,
+        kIndex4,
+        kIndex,
+        kRGB,
+        kBGR,
+        kRGBX,
+        kBGRX,
+        kRGBA,
+        kBGRA,
+        kRGB_565,
     };
 
-    static int BytesPerPixel(SrcConfig sc) {
+    /*
+     *
+     * Result code for the alpha components of a row.
+     *
+     */
+    typedef uint16_t ResultAlpha;
+    static const ResultAlpha kOpaque_ResultAlpha = 0xFFFF;
+    static const ResultAlpha kTransparent_ResultAlpha = 0x0000;
+    static const uint8_t kMaxAlphaInit = 0xFF;
+    static const uint8_t kZeroAlphaInit = 0x00;
+
+    /*
+     *
+     * Checks if the result of decoding a row indicates that the row was
+     * transparent.
+     *
+     */
+    static bool IsTransparent(ResultAlpha r) {
+        return kTransparent_ResultAlpha == r;
+    }
+
+    /*
+     *
+     * Checks if the result of decoding a row indicates that the row was
+     * opaque.
+     *
+     */
+    static bool IsOpaque(ResultAlpha r) {
+        return kOpaque_ResultAlpha == r;
+    }
+    
+    /*
+     *
+     * Constructs the proper result code based on accumulated alpha masks
+     *
+     */
+    static ResultAlpha GetResult(uint8_t zeroAlpha, uint8_t maxAlpha);
+
+    /*
+     *
+     * Returns bytes per pixel if bits per pixel >= 8

[scroggo, 2015/03/12 19:58:40]

I'm ambivalent about this. The tricky part is that the caller needs to know
whether it's bytes or bits.

Just to clarify: I *do* think it's good to store the one we care about down
below, and pass it to each call to fRowProc. It just seems a little weird that
this function doesn't specify whether its answer is in bits or bytes.

[msarett, 2015/03/12 21:59:41]

Done.

+     * Returns bits per pixel otherwise
+     *
+     */
+    static int DeltaSrc(SrcConfig sc) {
         switch (sc) {
+            case kIndex1:
+                return 1;
+            case kIndex2:
+                return 2;
+            case kIndex4:
+                return 4;
             case kGray:
             case kIndex:
                 return 1;
+            case kRGB_565:
+                return 2;
             case kRGB:
+            case kBGR:
                 return 3;
             case kRGBX:
             case kRGBA:
+            case kBGRX:
+            case kBGRA:
                 return 4;
-            case kRGB_565:
-                return 2;
             default:
-                SkDebugf("invalid source config passed to BytesPerPixel\n");
-                return -1;
+                SkASSERT(false);
+                return 0;
         }
     }
 
     /**
      *  Create a new SkSwizzler.
      *  @param sc SrcConfig
      *  @param info dimensions() describe both the src and the dst.
      *              Other fields describe the dst.
      *  @param dst Destination to write pixels. Must match info and dstRowBytes
      *  @param dstRowBytes rowBytes for dst.
      *  @param skipZeroes Whether to skip writing zeroes. Useful if dst is
      *              zero-initialized. The implementation may or may not respect this.
      *  @return A new SkSwizzler or NULL on failure.
      */
     static SkSwizzler* CreateSwizzler(SrcConfig sc, const SkPMColor* ctable,
                                       const SkImageInfo& info, void* dst,
                                       size_t dstRowBytes, bool skipZeroes);
+
     /**
      *  Swizzle the next line. Call height times, once for each row of source.
      *  @param src The next row of the source data.
-     *  @return Whether the row had non-opaque alpha.
+     *  @return A result code describing if the row was fully opaque, fully
+     *          transparent, or neither
      */
-    bool next(const uint8_t* SK_RESTRICT src);
+    ResultAlpha next(const uint8_t* SK_RESTRICT src);
+
+    /**
+     *
+     * Alternate version of next that allows the caller to specify the row.
+     * It is very important to only use one version of next.  Since the other
+     * version modifies the dst pointer, it will change the behavior of this
+     * function.  We will check this in Debug mode.
+     *
+     */
+    ResultAlpha next(const uint8_t* SK_RESTRICT src, int y);
 private:
+
+#ifdef SK_DEBUG
+    /*
+     *
+     * Keep track of which version of next the caller is using
+     *
+     */
+    enum NextMode {
+        kUninitialized_NextMode,
+        kConsecutive_NextMode,
+        kDesignateRow_NextMode,
+    };
+
+    NextMode fNextMode;
+#endif
+
     /**
      *  Method for converting raw data to Skia pixels.
      *  @param dstRow Row in which to write the resulting pixels.
      *  @param src Row of src data, in format specified by SrcConfig
      *  @param width Width in pixels
-     *  @param bpp bytes per pixel of the source.
+     *  @param deltaSrc if bitsPerPixel >= 8, deltaSrc is bytesPerPixel
+     *                  else, deltaSrc is bitsPerPixel
      *  @param y Line of source.
      *  @param ctable Colors (used for kIndex source).
      */
-    typedef bool (*RowProc)(void* SK_RESTRICT dstRow,
-                            const uint8_t* SK_RESTRICT src,
-                            int width, int bpp, int y,
-                            const SkPMColor ctable[]);
+    typedef ResultAlpha (*RowProc)(void* SK_RESTRICT dstRow,
+                                   const uint8_t* SK_RESTRICT src,
+                                   int width, int deltaSrc, int y,
+                                   const SkPMColor ctable[]);
 
     const RowProc       fRowProc;
-    const SkPMColor*    fColorTable;    // Unowned pointer
-    const int           fSrcPixelSize;
+    const SkPMColor*    fColorTable;      // Unowned pointer
+    const int           fDeltaSrc;        // if bitsPerPixel >= 8
+                                          //     deltaSrc is bytesPerPixel
+                                          // else
+                                          //     deltaSrc is bitsPerPixel
     const SkImageInfo   fDstInfo;
     void*               fDstRow;
     const size_t        fDstRowBytes;
     int                 fCurrY;
 
-    SkSwizzler(RowProc proc, const SkPMColor* ctable, int srcBpp,
+    SkSwizzler(RowProc proc, const SkPMColor* ctable, int deltaSrc,
                const SkImageInfo& info, void* dst, size_t rowBytes);
 
 };
 #endif // SkSwizzler_DEFINED