Bmp Image Decoding

src/codec/SkSwizzler.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkColorPriv.h"
 #include "SkSwizzler.h"
 #include "SkTemplates.h"
 
-// index
-
 #define A32_MASK_IN_PLACE   (SkPMColor)(SK_A32_MASK << SK_A32_SHIFT)
 
-static bool swizzle_index_to_n32(void* SK_RESTRICT dstRow,
-                                 const uint8_t* SK_RESTRICT src,
-                                 int width, int deltaSrc, int, const SkPMColor ctable[]) {
+// kIndex1, kIndex2, kIndex4
+
+static bool swizzle_small_index_to_n32(void* SK_RESTRICT dstRow,
+                                       const uint8_t* SK_RESTRICT src,
+                                       int width, int bitsPerPixel, int,
+                                       const SkPMColor ctable[],
+                                       const SkSwizzler::ColorMasks,
+                                       const SkSwizzler::ZeroAlpha, bool*,
+                                       bool*) {
 
     SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
     SkPMColor cc = A32_MASK_IN_PLACE;
+    const uint32_t pixelsPerByte = 8 / bitsPerPixel;
+    const uint32_t rowBytes = (width + pixelsPerByte - 1) / pixelsPerByte;
+    const uint8_t mask = (1 << bitsPerPixel) - 1;
+
+    uint32_t x = 0;
+    for (uint32_t byte = 0; byte < rowBytes; byte++) {
+        uint8_t pixelData = src[byte];
+        for (uint32_t p = 0; p < pixelsPerByte && x < width; p++) {
+            uint8_t index = (pixelData >> (8 - bitsPerPixel)) & mask;
+            dst[x] = ctable[index];
+            cc &= ctable[index];
+            pixelData <<= bitsPerPixel;
+            x++;
+        }
+    }
+    return cc != A32_MASK_IN_PLACE;
+}
+
+// kIndex
+
+static bool swizzle_index_to_n32(void* SK_RESTRICT dstRow,
+                                const uint8_t* SK_RESTRICT src,
+                                int width, int bitsPerPixel, int,
+                                const SkPMColor ctable[],
+                                const SkSwizzler::ColorMasks,
+                                const SkSwizzler::ZeroAlpha, bool*, bool*) {
+
+    SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
+    SkPMColor cc = A32_MASK_IN_PLACE;
     for (int x = 0; x < width; x++) {
         SkPMColor c = ctable[*src];
         cc &= c;
         dst[x] = c;
-        src += deltaSrc;
+        src++;
     }
     return cc != A32_MASK_IN_PLACE;
 }
 
 static bool swizzle_index_to_n32_skipZ(void* SK_RESTRICT dstRow,
-                                      const uint8_t* SK_RESTRICT src,
-                                      int width, int deltaSrc, int,
-                                      const SkPMColor ctable[]) {
+                                       const uint8_t* SK_RESTRICT src,
+                                       int width, int bitsPerPixel, int,
+                                       const SkPMColor ctable[],
+                                       const SkSwizzler::ColorMasks,
+                                       const SkSwizzler::ZeroAlpha, bool*,
+                                       bool*) {
 
     SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
     SkPMColor cc = A32_MASK_IN_PLACE;
     for (int x = 0; x < width; x++) {
         SkPMColor c = ctable[*src];
         cc &= c;
         if (c != 0) {
             dst[x] = c;
         }
+        src++;
+    }
+    return cc != A32_MASK_IN_PLACE;
+}
+
+#undef A32_MASK_IN_PLACE
+
+// mask
+
+/**
+ *
+ * Used to convert 1-7 bit color components into 8-bit color components
+ *
+ */
+const uint8_t nBitTo8BitlookupTable[] = {
+    // 1 bit
+    0, 255,
+    // 2 bits
+    0, 85, 170, 255,
+    // 3 bits
+    0, 36, 73, 109, 146, 182, 219, 255,
+    // 4 bits
+    0, 17, 34, 51, 68, 85, 102, 119, 136, 153, 170, 187, 204, 221, 238, 255,
+    // 5 bits
+    0, 8, 16, 25, 33, 41, 49, 58, 66, 74, 82, 90, 99, 107, 115, 123, 132, 140,
+    148, 156, 165, 173, 181, 189, 197, 206, 214, 222, 230, 239, 247, 255,
+    // 6 bits
+    0, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 45, 49, 53, 57, 61, 65, 69, 73,
+    77, 81, 85, 89, 93, 97, 101, 105, 109, 113, 117, 121, 125, 130, 134, 138,
+    142, 146, 150, 154, 158, 162, 166, 170, 174, 178, 182, 186, 190, 194, 198,
+    202, 206, 210, 215, 219, 223, 227, 231, 235, 239, 243, 247, 251, 255,
+    // 7 bits
+    0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38,
+    40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76,
+    78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, 110,
+    112, 114, 116, 118, 120, 122, 124, 126, 129, 131, 133, 135, 137, 139, 141,
+    143, 145, 147, 149, 151, 153, 155, 157, 159, 161, 163, 165, 167, 169, 171,
+    173, 175, 177, 179, 181, 183, 185, 187, 189, 191, 193, 195, 197, 199, 201,
+    203, 205, 207, 209, 211, 213, 215, 217, 219, 221, 223, 225, 227, 229, 231,
+    233, 235, 237, 239, 241, 243, 245, 247, 249, 251, 253, 255
+};
+
+/*
+ *
+ * Convert an n bit component to an 8-bit component
+ *
+ */
+static uint8_t convertNTo8(uint32_t component, uint32_t n) {
+    if (0 == n) {
+        return 0;
+    } else if (8 > n) {
+        return nBitTo8BitlookupTable[(1 << n) - 2 + component];
+    } else if (8 == n) {
+        return component;
+    } else {
+        SkDebugf("Error: too many bits for lookup table.\n");
+        return 0;
+    }
+}
+
+/*
+ *
+ * For a continuous bit mask (ex: 0011100), retrieves the size of the mask and
+ * the trailing zeros
+ *
+ */
+static void getMaskInfo(uint32_t mask, uint32_t bPP, uint32_t* size,
+        uint32_t* shift) {
+    // For empty masks, set zeros and return
+    uint32_t tempMask = mask;
+    if (!tempMask) {
+        *size = 0;
+        *shift = 0;
+        return;
+    }
+
+    // Count trailing zeros
+    int zeros = 0;
+    for (; !(tempMask & 1); tempMask >>= 1) {
+        zeros++;
+    }
+
+    // Count mask size
+    int count = 0;
+    for (; tempMask & 1; tempMask >>= 1) {
+        count++;
+    }
+
+    // We will use a maximum of 8 bits for the size, truncate some of the mask
+    // bits if necessary
+    if (count > 8) {
+        *shift = count - 8 + zeros;
+        *size = 8;
+    } else {
+        *shift = zeros;
+        *size = count;
+    }
+    return;
+}
+
+// kMask16
+
+static bool swizzle_mask16_to_n32(void* SK_RESTRICT dstRow,
+                                  const uint8_t* SK_RESTRICT src,
+                                  int width, int bitsPerPixel, int,
+                                  const SkPMColor ctable[],
+                                  const SkSwizzler::ColorMasks masks,
+                                  const SkSwizzler::ZeroAlpha zeroAlpha,
+                                  bool* seenNonZeroAlphaPtr,
+                                  bool* zeroPrevRowsPtr) {
+    // Load the bit masks
+    uint32_t redMask = masks.redMask;
+    uint32_t greenMask = masks.greenMask;
+    uint32_t blueMask = masks.blueMask;
+    uint32_t alphaMask = masks.alphaMask;
+    uint32_t rBits, rShift, gBits, gShift, bBits, bShift, aBits, aShift;
+    getMaskInfo(redMask, bitsPerPixel, &rBits, &rShift);
+    getMaskInfo(greenMask, bitsPerPixel, &gBits, &gShift);
+    getMaskInfo(blueMask, bitsPerPixel, &bBits, &bShift);
+    getMaskInfo(alphaMask, bitsPerPixel, &aBits, &aShift);
+
+    // Use the masks to decode to the destination
+    SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
+    int x = 0;
+    for (uint32_t p = 0; p < width * 2; p += 2) {
+        uint16_t pixel = src[p] | (src[p + 1] << 8);
+        uint8_t red = convertNTo8((pixel & redMask) >> rShift, rBits);
+        uint8_t green = convertNTo8((pixel & greenMask) >> gShift, gBits);
+        uint8_t blue = convertNTo8((pixel & blueMask) >> bShift, bBits);
+        uint8_t alpha = convertNTo8((pixel & alphaMask) >> aShift, aBits);
+
+        // We must respect the alpha channel for bmp V4+.  However, if it is
+        // all zeros, we will display the image as opaque rather than
+        // transparent.  This may require redoing some of the processing.
+        if (SkSwizzler::kTransparentAsOpaque_ZeroAlpha == zeroAlpha &&
+                *seenNonZeroAlphaPtr) {
+            dst[x] = SkPreMultiplyColor(SkColorSetARGBInline(
+                    alpha, red, green, blue));
+            x++;
+        } else if (!alpha) {
+            dst[x] = SkPackARGB32(0xFF, red, green, blue);
+            x++;
+        } else {
+            *zeroPrevRowsPtr = true;
+            *seenNonZeroAlphaPtr = true;
+            x = 0;
+            p = -2;
+        }
+    }
+    return *seenNonZeroAlphaPtr;
+}
+
+// kMask24
+
+static bool swizzle_mask24_to_n32(void* SK_RESTRICT dstRow,
+                                  const uint8_t* SK_RESTRICT src,
+                                  int width, int bitsPerPixel, int,
+                                  const SkPMColor ctable[],
+                                  const SkSwizzler::ColorMasks masks,
+                                  const SkSwizzler::ZeroAlpha zeroAlpha,
+                                  bool* seenNonZeroAlphaPtr,
+                                  bool* zeroPrevRowsPtr) {
+    // Load the bit masks
+    uint32_t redMask = masks.redMask;
+    uint32_t greenMask = masks.greenMask;
+    uint32_t blueMask = masks.blueMask;
+    uint32_t alphaMask = masks.alphaMask;
+    uint32_t rBits, rShift, gBits, gShift, bBits, bShift, aBits, aShift;
+    getMaskInfo(redMask, bitsPerPixel, &rBits, &rShift);
+    getMaskInfo(greenMask, bitsPerPixel, &gBits, &gShift);
+    getMaskInfo(blueMask, bitsPerPixel, &bBits, &bShift);
+    getMaskInfo(alphaMask, bitsPerPixel, &aBits, &aShift);
+
+    // Use the masks to decode to the destination
+    SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
+    int x = 0;
+    for (uint32_t p = 0; p < width * 3; p += 3) {
+        uint32_t pixel = src[p] | (src[p + 1] << 8) | src[p + 2] << 16;
+        uint8_t red = convertNTo8((pixel & redMask) >> rShift, rBits);
+        uint8_t green = convertNTo8((pixel & greenMask) >> gShift, gBits);
+        uint8_t blue = convertNTo8((pixel & blueMask) >> bShift, bBits);
+        uint8_t alpha = convertNTo8((pixel & alphaMask) >> aShift, aBits);
+
+        // We must respect the alpha channel for bmp V4+.  However, if it is
+        // all zeros, we will display the image as opaque rather than
+        // transparent.  This may require redoing some of the processing.
+        if (SkSwizzler::kTransparentAsOpaque_ZeroAlpha == zeroAlpha &&
+                *seenNonZeroAlphaPtr) {
+            dst[x] = SkPreMultiplyColor(SkColorSetARGBInline(
+                    alpha, red, green, blue));
+            x++;
+        } else if (!alpha) {
+            dst[x] = SkPackARGB32(0xFF, red, green, blue);
+            x++;
+        } else {
+            *zeroPrevRowsPtr = true;
+            *seenNonZeroAlphaPtr = true;
+            x = 0;
+            p = -3;
+        }
+    }
+    return *seenNonZeroAlphaPtr;
+}
+
+// kMask32
+
+static bool swizzle_mask32_to_n32(void* SK_RESTRICT dstRow,
+                                  const uint8_t* SK_RESTRICT src,
+                                  int width, int bitsPerPixel, int,
+                                  const SkPMColor ctable[],
+                                  const SkSwizzler::ColorMasks masks,
+                                  const SkSwizzler::ZeroAlpha zeroAlpha,
+                                  bool* seenNonZeroAlphaPtr,
+                                  bool* zeroPrevRowsPtr) {
+    // Load the bit masks
+    uint32_t redMask = masks.redMask;
+    uint32_t greenMask = masks.greenMask;
+    uint32_t blueMask = masks.blueMask;
+    uint32_t alphaMask = masks.alphaMask;
+    uint32_t rBits, rShift, gBits, gShift, bBits, bShift, aBits, aShift;
+    getMaskInfo(redMask, bitsPerPixel, &rBits, &rShift);
+    getMaskInfo(greenMask, bitsPerPixel, &gBits, &gShift);
+    getMaskInfo(blueMask, bitsPerPixel, &bBits, &bShift);
+    getMaskInfo(alphaMask, bitsPerPixel, &aBits, &aShift);
+
+    // Use the masks to decode to the destination
+    SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
+    int x = 0;
+    for (uint32_t p = 0; p < width * 4; p += 4) {
+        uint32_t pixel = src[p] | (src[p + 1] << 8) | src[p + 2] << 16 |
+                src[p + 3] << 24;
+        uint8_t red = convertNTo8((pixel & redMask) >> rShift, rBits);
+        uint8_t green = convertNTo8((pixel & greenMask) >> gShift, gBits);
+        uint8_t blue = convertNTo8((pixel & blueMask) >> bShift, bBits);
+        uint8_t alpha = convertNTo8((pixel & alphaMask) >> aShift, aBits);
+
+        // We must respect the alpha channel for bmp V4+.  However, if it is
+        // all zeros, we will display the image as opaque rather than
+        // transparent.  This may require redoing some of the processing.
+        if (SkSwizzler::kTransparentAsOpaque_ZeroAlpha == zeroAlpha &&
+                *seenNonZeroAlphaPtr) {
+            dst[x] = SkPreMultiplyColor(SkColorSetARGBInline(
+                    alpha, red, green, blue));
+            x++;
+        } else if (!alpha) {
+            dst[x] = SkPackARGB32(0xFF, red, green, blue);
+            x++;
+        } else {
+            *zeroPrevRowsPtr = true;
+            *seenNonZeroAlphaPtr = true;
+            x = 0;
+            p = -4;
+        }
+    }
+    return *seenNonZeroAlphaPtr;
+}
+
+// kBGRX and kBGR
+
+static bool swizzle_bgrx_to_n32(void* SK_RESTRICT dstRow,
+                                const uint8_t* SK_RESTRICT src,
+                                int width, int bitsPerPixel, int,
+                                const SkPMColor[],
+                                const SkSwizzler::ColorMasks,
+                                const SkSwizzler::ZeroAlpha, bool*, bool*) {
+    SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
+    int deltaSrc = bitsPerPixel / 8;
+    for (int x = 0; x < width; x++) {
+        dst[x] = SkPackARGB32(0xFF, src[2], src[1], src[0]);
         src += deltaSrc;
     }
-    return cc != A32_MASK_IN_PLACE;
-}
-
-#undef A32_MASK_IN_PLACE
+    return false;
+}
+
+// kBGRA
+
+static bool swizzle_bgra_to_n32(void* SK_RESTRICT dstRow,
+                                const uint8_t* SK_RESTRICT src,
+                                int width, int bitsPerPixel, int,
+                                const SkPMColor[],
+                                const SkSwizzler::ColorMasks masks,
+                                const SkSwizzler::ZeroAlpha zeroAlpha,
+                                bool* seenNonZeroAlphaPtr,
+                                bool* zeroPrevRowsPtr) {
+    SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
+    uint32_t alphaMask = masks.alphaMask;
+    int deltaSrc = bitsPerPixel / 8;
+    const uint8_t* srcStart = src;
+    for (int x = 0; x < width; x++) {
+        uint8_t alpha = alphaMask & src[3];
+        // We must respect the alpha channel for bmp V4+.  However, if it is
+        // all zeros, we will display the image as opaque rather than
+        // transparent.  This may require redoing some of the processing.
+        if (SkSwizzler::kNormal_ZeroAlpha == zeroAlpha ||
+                *seenNonZeroAlphaPtr) {
+            dst[x] = SkPreMultiplyARGB(alpha, src[2], src[1], src[0]);
+            src += deltaSrc;
+        } else if (!alpha) {
+            dst[x] = SkPackARGB32(0xFF, src[2], src[1], src[0]);
+            src += deltaSrc;
+        } else {
+            *zeroPrevRowsPtr = true;
+            *seenNonZeroAlphaPtr = true;
+            int x = -1;
+            src = srcStart;
+        }
+    }
+    return *seenNonZeroAlphaPtr;
+}
 
 // n32
 static bool swizzle_rgbx_to_n32(void* SK_RESTRICT dstRow,
                                 const uint8_t* SK_RESTRICT src,
-                                int width, int deltaSrc, int, const SkPMColor[]) {
-    SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
+                                int width, int bitsPerPixel, int,
+                                const SkPMColor[],
+                                const SkSwizzler::ColorMasks,
+                                const SkSwizzler::ZeroAlpha, bool*, bool*) {
+    SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
+    int deltaSrc = bitsPerPixel / 8;
     for (int x = 0; x < width; x++) {
         dst[x] = SkPackARGB32(0xFF, src[0], src[1], src[2]);
         src += deltaSrc;
     }
     return false;
 }
 
 static bool swizzle_rgba_to_n32_premul(void* SK_RESTRICT dstRow,
                                        const uint8_t* SK_RESTRICT src,
-                                       int width, int deltaSrc, int, const SkPMColor[]) {
+                                       int width, int bitsPerPixel, int,
+                                       const SkPMColor[],
+                                       const SkSwizzler::ColorMasks,
+                                       const SkSwizzler::ZeroAlpha, bool*,
+                                       bool*) {
     SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
+    int deltaSrc = bitsPerPixel / 8;
     unsigned alphaMask = 0xFF;
     for (int x = 0; x < width; x++) {
         unsigned alpha = src[3];
         dst[x] = SkPreMultiplyARGB(alpha, src[0], src[1], src[2]);
         src += deltaSrc;
         alphaMask &= alpha;
     }
     return alphaMask != 0xFF;
 }
 
 static bool swizzle_rgba_to_n32_unpremul(void* SK_RESTRICT dstRow,
                                          const uint8_t* SK_RESTRICT src,
-                                         int width, int deltaSrc, int,
-                                         const SkPMColor[]) {
+                                         int width, int bitsPerPixel, int,
+                                         const SkPMColor[],
+                                         const SkSwizzler::ColorMasks,
+                                         const SkSwizzler::ZeroAlpha, bool*,
+                                         bool*) {
     uint32_t* SK_RESTRICT dst = reinterpret_cast<uint32_t*>(dstRow);
+    int deltaSrc = bitsPerPixel / 8;
     unsigned alphaMask = 0xFF;
     for (int x = 0; x < width; x++) {
         unsigned alpha = src[3];
         dst[x] = SkPackARGB32NoCheck(alpha, src[0], src[1], src[2]);
         src += deltaSrc;
         alphaMask &= alpha;
     }
     return alphaMask != 0xFF;
 }
 
 static bool swizzle_rgba_to_n32_premul_skipZ(void* SK_RESTRICT dstRow,
                                              const uint8_t* SK_RESTRICT src,
-                                             int width, int deltaSrc, int,
-                                             const SkPMColor[]) {
+                                             int width, int bitsPerPixel, int,
+                                             const SkPMColor[],
+                                             const SkSwizzler::ColorMasks,
+                                             const SkSwizzler::ZeroAlpha,
+                                             bool*, bool*) {
     SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
+    int deltaSrc = bitsPerPixel / 8;
     unsigned alphaMask = 0xFF;
     for (int x = 0; x < width; x++) {
         unsigned alpha = src[3];
         if (0 != alpha) {
             dst[x] = SkPreMultiplyARGB(alpha, src[0], src[1], src[2]);
         }
         src += deltaSrc;
         alphaMask &= alpha;
     }
     return alphaMask != 0xFF;
 }
 
 /**
     FIXME: This was my idea to cheat in order to continue taking advantage of skipping zeroes.
     This would be fine for drawing normally, but not for drawing with transfer modes. Being
     honest means we can draw correctly with transfer modes, with the cost of not being able
     to take advantage of Android's free unwritten pages. Something to keep in mind when we
     decide whether to switch to unpremul default.
 static bool swizzle_rgba_to_n32_unpremul_skipZ(void* SK_RESTRICT dstRow,
                                                const uint8_t* SK_RESTRICT src,
-                                               int width, int deltaSrc, int,
+                                               int width, int bitsPerPixel,
                                                const SkPMColor[]) {
     SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
     unsigned alphaMask = 0xFF;
     for (int x = 0; x < width; x++) {
         unsigned alpha = src[3];
         // NOTE: We cheat here. The caller requested unpremul and skip zeroes. It's possible
         // the color components are not zero, but we skip them anyway, meaning they'll remain
         // zero (implied by the request to skip zeroes).
         if (0 != alpha) {
             dst[x] = SkPackARGB32NoCheck(alpha, src[0], src[1], src[2]);
         }
         src += deltaSrc;
         alphaMask &= alpha;
     }
     return alphaMask != 0xFF;
 }
 */
 
-SkSwizzler* SkSwizzler::CreateSwizzler(SkSwizzler::SrcConfig sc, const SkPMColor* ctable,
+SkSwizzler* SkSwizzler::CreateSwizzler(SkSwizzler::SrcConfig sc,
+                                       const SkPMColor* ctable,
                                        const SkImageInfo& info, void* dst,
-                                       size_t dstRowBytes, bool skipZeroes) {
-    if (info.colorType() == kUnknown_SkColorType) {
+                                       size_t dstRowBytes, bool skipZeroes,
+                                       const ColorMasks bitMasks,
+                                       const ZeroAlpha zeroAlpha,
+                                       const RowOrder rowOrder) {
+    if (kUnknown_SkColorType == info.colorType()) {
         return NULL;
     }
     if (info.minRowBytes() > dstRowBytes) {
         return  NULL;
     }
-    if (kIndex == sc && NULL == ctable) {
+    if ((kIndex == sc || kIndex4 == sc || kIndex2 == sc || kIndex1 == sc)
+            && NULL == ctable) {
         return NULL;
     }
     RowProc proc = NULL;
     switch (sc) {
+        case kIndex1:
+        case kIndex2:
+        case kIndex4:
+            switch (info.colorType()) {
+                case kN32_SkColorType:
+                    proc = &swizzle_small_index_to_n32;
+                    break;
+                default:
+                    break;
+            }
+            break;
         case kIndex:
             switch (info.colorType()) {
                 case kN32_SkColorType:
-                    // We assume the color premultiplied ctable (or not) as desired.
-                    if (skipZeroes) {
-                        proc = &swizzle_index_to_n32_skipZ;
-                    } else {
-                        proc = &swizzle_index_to_n32;
-                    }
+                    proc = &swizzle_index_to_n32;
                     break;
-                    
                 default:
                     break;
             }
+            break;
+        case kMask16:
+            switch (info.colorType()) {
+                case kN32_SkColorType:
+                    proc = &swizzle_mask16_to_n32;
+                    break;
+                default:
+                    break;
+            }
+            break;
+        case kMask24:
+            switch (info.colorType()) {
+                case kN32_SkColorType:
+                    proc = &swizzle_mask24_to_n32;
+                    break;
+                default:
+                    break;
+            }
+            break;
+        case kMask32:
+            switch (info.colorType()) {
+                case kN32_SkColorType:
+                    proc = &swizzle_mask32_to_n32;
+                    break;
+                default:
+                    break;
+            }
+            break;
+        case kBGR:
+        case kBGRX:
+            switch (info.colorType()) {
+                case kN32_SkColorType:
+                    proc = &swizzle_bgrx_to_n32;
+                    break;
+                default:
+                    break;
+            }
+            break;
+        case kBGRA:
+            switch (info.colorType()) {
+                case kN32_SkColorType:
+                    proc = &swizzle_bgra_to_n32;
+                    break;
+                default:
+                    break;
+            }
             break;
         case kRGBX:
             // TODO: Support other swizzles.
             switch (info.colorType()) {
                 case kN32_SkColorType:
                     proc = &swizzle_rgbx_to_n32;
                     break;
                 default:
                     break;
             }
             break;
         case kRGBA:
             switch (info.colorType()) {
                 case kN32_SkColorType:
                     if (info.alphaType() == kUnpremul_SkAlphaType) {
                         // Respect skipZeroes?
                         proc = &swizzle_rgba_to_n32_unpremul;
                     } else {
                         if (skipZeroes) {
                             proc = &swizzle_rgba_to_n32_premul_skipZ;
                         } else {
                             proc = &swizzle_rgba_to_n32_premul;
                         }
                     }
                     break;
                 default:
                     break;
             }
             break;
+        case kRGB:
+            switch (info.colorType()) {
+                case kN32_SkColorType:
+                    proc = &swizzle_rgbx_to_n32;
+                    break;
+                default:
+                    break;
+            }
+            break;
         default:
             break;
     }
     if (NULL == proc) {
         return NULL;
     }
-    return SkNEW_ARGS(SkSwizzler, (proc, ctable, BytesPerPixel(sc), info, dst, dstRowBytes));
+    return SkNEW_ARGS(SkSwizzler, (proc, ctable, BitsPerPixel(sc), info, dst,
+                                   dstRowBytes, bitMasks, zeroAlpha, rowOrder));
 }
 
-SkSwizzler::SkSwizzler(RowProc proc, const SkPMColor* ctable, int srcBpp,
-                       const SkImageInfo& info, void* dst, size_t rowBytes)
+SkSwizzler::SkSwizzler(RowProc proc, const SkPMColor* ctable,
+                       int srcBitsPerPixel, const SkImageInfo& info, void* dst,
+                       size_t rowBytes, const ColorMasks bitMasks,
+                       const ZeroAlpha zeroAlpha, const RowOrder rowOrder)
     : fRowProc(proc)
     , fColorTable(ctable)
-    , fSrcPixelSize(srcBpp)
+    , fSrcBitsPerPixel(srcBitsPerPixel)
     , fDstInfo(info)
     , fDstRow(dst)
     , fDstRowBytes(rowBytes)
     , fCurrY(0)
+    , fBitMasks(bitMasks)
+    , fZeroAlpha(zeroAlpha)
+    , fRowOrder(rowOrder)
+    , fSeenNonZeroAlpha(false)
+    , fZeroPrevRows(false)
 {
 }
 
 bool SkSwizzler::next(const uint8_t* SK_RESTRICT src) {
     SkASSERT(fCurrY < fDstInfo.height());
-    const bool hadAlpha = fRowProc(fDstRow, src, fDstInfo.width(), fSrcPixelSize,
-                                   fCurrY, fColorTable);
+
+    // On the first iteration, if the image is inverted, start at the bottom
+    if (0 == fCurrY && kBottomUp_RowOrder == fRowOrder) {
+        fDstRow = SkTAddOffset<void>(fDstRow,
+                fDstRowBytes * (fDstInfo.height() - 1));
+    }
+
+    // Decode a row
+    const bool hadAlpha = fRowProc(fDstRow, src, fDstInfo.width(),
+            fSrcBitsPerPixel, fCurrY, fColorTable, fBitMasks, fZeroAlpha,
+            &fSeenNonZeroAlpha, &fZeroPrevRows);
+
+    // This flag indicates that we have decoded the image as opaque instead of
+    // transparent, and we just realized that it should have been transparent.
+    // To fix this, we zero the rows that have already been decoded.
+    if (fZeroPrevRows) {
+        void* dstRow;
+        if (kTopDown_RowOrder == fRowOrder) {
+            void* dstStart = SkTAddOffset<void>(fDstRow, -fCurrY*fDstRowBytes);
+            memset(dstStart, 0, fCurrY*fDstRowBytes);
+        } else {
+            void* dstStart = SkTAddOffset<void>(fDstRow, fDstRowBytes);
+            memset(dstStart, 0, fCurrY*fDstRowBytes);
+        }
+        fZeroPrevRows = false;
+    }
+
+    // Move to the next row and return the result
     fCurrY++;
-    fDstRow = SkTAddOffset<void>(fDstRow, fDstRowBytes);
+    if (kTopDown_RowOrder == fRowOrder) {
+        fDstRow = SkTAddOffset<void>(fDstRow, fDstRowBytes);
+    } else {
+        fDstRow = SkTAddOffset<void>(fDstRow, -fDstRowBytes);
+    }
     return hadAlpha;
 }