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,
+        kMask16,
+        kMask24,
+        kMask32
     };
 
-    static int BytesPerPixel(SrcConfig sc) {
+    /**
+     *  In mask SrcConfigs, used as bit masks for color components.
+     */
+    struct ColorMasks {
+        uint32_t redMask;
+        uint32_t greenMask;
+        uint32_t blueMask;
+        uint32_t alphaMask;
+    };
+
+    /**
+     * Describes if rows of the input start at the top or bottom of the image.
+     */
+    enum RowOrder {
+        kTopDown,

[scroggo, 2015/02/27 17:04:03]

Style nit: In Skia, we append the enum type name to each enum. So this should
be:

kTopDown_RowOrder

etc.

+        kBottomUp
+    };
+
+    /**
+     * Describes if we will render fully transparent images as opaque.
+     */
+    enum ZeroAlpha {
+        kTransparentAsOpaque,
+        kNormal
+    };
+
+    static int BitsPerPixel(SrcConfig sc) {
         switch (sc) {
-            case kGray:
+            case kIndex1:
+                return 1;
+            case kIndex2:
+                return 2;
+            case kIndex4:
+                return 4;
             case kIndex:
-                return 1;
+                return 8;
+            case kRGB_565:
+            case kMask16:
+                return 16;
             case kRGB:
-                return 3;
+            case kBGR:
+            case kMask24:
+                return 24;
             case kRGBX:
             case kRGBA:
-                return 4;
-            case kRGB_565:
-                return 2;
+            case kBGRX:
+            case kBGRA:
+            case kMask32:
+                return 32;
         }
     }
 
     /**
      *  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.
+     *  @param bitMasks Masks used to separate the color components of a pixel
+     *  @param zeroAlpha Some inputs (bmp) have an alpha channel that is unused.
+     *              Users of this channel often fill it with zeros, but still
+     *              expect the image to be opaque.  When zeroAlpha is
+     *              kTransparentAsOpaque, completely transparent images should
+     *              be rendered as opaque. Images that are not completely
+     *              transparent should be treated normally.
+     *  @param rowOrder Order in which input rows are swizzled
      *  @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);
+                                      size_t dstRowBytes, bool skipZeroes,
+                                      const ColorMasks* bitMasks = NULL,
+                                      const ZeroAlpha zeroAlpha = kNormal,
+                                      const RowOrder rowOrder = kTopDown);
     /**
      *  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.
      */
     bool next(const uint8_t* SK_RESTRICT src);
 private:
     /**
      *  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 y Line of source.
      *  @param ctable Colors (used for kIndex source).
+     *  @param masks Bit masks used to separate the color components of a pixel
+     *  @param zeroAlpha Some inputs (bmp) have an alpha channel that is unused.
+     *              Users of this channel often fill it with zeros, but still
+     *              expect the image to be opaque.  When zeroAlpha is
+     *              kTransparentAsOpaque, completely transparent images should
+     *              be rendered as opaque. Images that are not completely
+     *              transparent should be treated normally.
+     *  @param seenNonZeroAlphaPtr A ptr to the field that indicates if we have
+     *              seen a non-zero alpha value in an image.  This is used in
+     *              conjunction with zeroAlpha to ensure accidentally fully
+     *              transparent images are rendered as opaque.
+     *  @param zeroPrevRowsPtr A ptr to the field that indicates if we need
+     *              to set all previously decoded rows as transparent.  This
+     *              occurs when we have decoded transparent rows as opaque
+     *              (because zeroAlpha is true), but then find a pixel that is
+     *              not transparent.  On this event, we must return to
+     *              previously decoded rows and set them as transparent.
      */
     typedef bool (*RowProc)(void* SK_RESTRICT dstRow,
                             const uint8_t* SK_RESTRICT src,
-                            int width, int bpp, int y,
-                            const SkPMColor ctable[]);
+                            int width, int bitsPerPixel, int y,
+                            const SkPMColor ctable[], const ColorMasks* masks,
+                            const ZeroAlpha zeroAlpha,
+                            bool* seenNonZeroAlphaPtr, bool* zeroPrevRowsPtr);
 
     const RowProc       fRowProc;
     const SkPMColor*    fColorTable;    // Unowned pointer
-    const int           fSrcPixelSize;
+    const ColorMasks*   fBitMasks;      // Unowned pointer
+    const int           fSrcBitsPerPixel;
     const SkImageInfo   fDstInfo;
     void*               fDstRow;
     const size_t        fDstRowBytes;
     int                 fCurrY;
+    const ZeroAlpha     fZeroAlpha;
+    const RowOrder      fRowOrder;
+    bool                fSeenNonZeroAlpha;
+    bool                fZeroPrevRows;
 
-    SkSwizzler(RowProc proc, const SkPMColor* ctable, int srcBpp,
-               const SkImageInfo& info, void* dst, size_t rowBytes);
+    SkSwizzler(RowProc proc, const SkPMColor* ctable, int srcBPP,
+               const SkImageInfo& info, void* dst, size_t rowBytes,
+               const ColorMasks* bitMasks, const ZeroAlpha zeroAlpha,
+               const RowOrder rowOrder);
 
 };
 #endif // SkSwizzler_DEFINED