Add an option on SkImageDecoder to skip writing 0s.

src/images/SkScaledBitmapSampler.cpp

Index: src/images/SkScaledBitmapSampler.cpp
diff --git a/src/images/SkScaledBitmapSampler.cpp b/src/images/SkScaledBitmapSampler.cpp
index 021f86ba868c14204af1c9d0ce27017f30943244..3bab8de9fd918079579c68d39da70d4f5998884f 100644
--- a/src/images/SkScaledBitmapSampler.cpp
+++ b/src/images/SkScaledBitmapSampler.cpp
@@ -25,6 +25,11 @@ static bool Sample_Gray_D8888(void* SK_RESTRICT dstRow,
     return false;
 }
 
+static SkScaledBitmapSampler::RowProc get_gray_to_8888_proc(const SkImageDecoder& decoder) {
+    // Dither, unpremul, and skipZeroes have no effect
+    return Sample_Gray_D8888;
+}
+
 static bool Sample_RGBx_D8888(void* SK_RESTRICT dstRow,
                               const uint8_t* SK_RESTRICT src,
                               int width, int deltaSrc, int, const SkPMColor[]) {
@@ -36,6 +41,11 @@ static bool Sample_RGBx_D8888(void* SK_RESTRICT dstRow,
     return false;
 }
 
+static SkScaledBitmapSampler::RowProc get_RGBx_to_8888_proc(const SkImageDecoder& decoder) {
+    // Dither, unpremul, and skipZeroes have no effect
+    return Sample_RGBx_D8888;
+}
+
 static bool Sample_RGBA_D8888(void* SK_RESTRICT dstRow,
                               const uint8_t* SK_RESTRICT src,
                               int width, int deltaSrc, int, const SkPMColor[]) {
@@ -50,6 +60,52 @@ static bool Sample_RGBA_D8888(void* SK_RESTRICT dstRow,
     return alphaMask != 0xFF;
 }
 
+static bool Sample_RGBA_D8888_Unpremul(void* SK_RESTRICT dstRow,

[scroggo, 2013/09/19 18:43:43]

This was moved from down below.

+                                       const uint8_t* SK_RESTRICT src,
+                                       int width, int deltaSrc, int,
+                                       const SkPMColor[]) {
+    uint32_t* SK_RESTRICT dst = reinterpret_cast<uint32_t*>(dstRow);
+    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 Sample_RGBA_D8888_SkipZ(void* SK_RESTRICT dstRow,
+                                    const uint8_t* SK_RESTRICT src,
+                                    int width, int deltaSrc, int,
+                                    const SkPMColor[]) {
+    SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
+    unsigned alphaMask = 0xFF;
+    for (int x = 0; x < width; x++) {
+        unsigned alpha = src[3];
+        if (0 != alpha) {

[scroggo, 2013/09/19 18:43:43]

This function is the same as Sample_RGBA_D8888, only we skip the write if 0 ==
alpha.

+            dst[x] = SkPreMultiplyARGB(alpha, src[0], src[1], src[2]);
+        }
+        src += deltaSrc;
+        alphaMask &= alpha;
+    }
+    return alphaMask != 0xFF;
+}
+
+static SkScaledBitmapSampler::RowProc get_RGBA_to_8888_proc(const SkImageDecoder& decoder) {
+    // Dither has no effect.
+    if (decoder.getRequireUnpremultipliedColors()) {
+        // We could check each component for a zero, at the expense of extra checks.
+        // For now, just return unpremul.
+        return Sample_RGBA_D8888_Unpremul;
+    }
+    // Supply the versions that premultiply the colors
+    if (decoder.getSkipWritingZeroes()) {
+        return Sample_RGBA_D8888_SkipZ;
+    }
+    return Sample_RGBA_D8888;
+}
+
 // 565
 
 static bool Sample_Gray_D565(void* SK_RESTRICT dstRow,
@@ -75,6 +131,14 @@ static bool Sample_Gray_D565_D(void* SK_RESTRICT dstRow,
     return false;
 }
 
+static SkScaledBitmapSampler::RowProc get_gray_to_565_proc(const SkImageDecoder& decoder) {
+    // Unpremul and skip zeroes make no difference
+    if (decoder.getDitherImage()) {
+        return Sample_Gray_D565_D;
+    }
+    return Sample_Gray_D565;
+}
+
 static bool Sample_RGBx_D565(void* SK_RESTRICT dstRow,
                              const uint8_t* SK_RESTRICT src,
                              int width, int deltaSrc, int, const SkPMColor[]) {
@@ -86,6 +150,28 @@ static bool Sample_RGBx_D565(void* SK_RESTRICT dstRow,
     return false;
 }
 
+static bool Sample_RGBx_D565_D(void* SK_RESTRICT dstRow,

[scroggo, 2013/09/19 18:43:43]

I moved this to put it next to Sample_RGBx_D565.

+                               const uint8_t* SK_RESTRICT src,
+                               int width, int deltaSrc, int y,
+                               const SkPMColor[]) {
+    uint16_t* SK_RESTRICT dst = (uint16_t*)dstRow;
+    DITHER_565_SCAN(y);
+    for (int x = 0; x < width; x++) {
+        dst[x] = SkDitherRGBTo565(src[0], src[1], src[2], DITHER_VALUE(x));
+        src += deltaSrc;
+    }
+    return false;
+}
+
+static SkScaledBitmapSampler::RowProc get_RGBx_to_565_proc(const SkImageDecoder& decoder) {
+    // Unpremul and skip zeroes make no difference
+    if (decoder.getDitherImage()) {
+        return Sample_RGBx_D565_D;
+    }
+    return Sample_RGBx_D565;
+}
+
+
 static bool Sample_D565_D565(void* SK_RESTRICT dstRow,
                              const uint8_t* SK_RESTRICT src,
                              int width, int deltaSrc, int, const SkPMColor[]) {
@@ -98,16 +184,9 @@ static bool Sample_D565_D565(void* SK_RESTRICT dstRow,
     return false;
 }
 
-static bool Sample_RGBx_D565_D(void* SK_RESTRICT dstRow,
-                               const uint8_t* SK_RESTRICT src,
-                           int width, int deltaSrc, int y, const SkPMColor[]) {
-    uint16_t* SK_RESTRICT dst = (uint16_t*)dstRow;
-    DITHER_565_SCAN(y);
-    for (int x = 0; x < width; x++) {
-        dst[x] = SkDitherRGBTo565(src[0], src[1], src[2], DITHER_VALUE(x));
-        src += deltaSrc;
-    }
-    return false;
+static SkScaledBitmapSampler::RowProc get_565_to_565_proc(const SkImageDecoder& decoder) {
+    // Unpremul, dither, and skip zeroes have no effect
+    return Sample_D565_D565;
 }
 
 // 4444
@@ -137,6 +216,14 @@ static bool Sample_Gray_D4444_D(void* SK_RESTRICT dstRow,
     return false;
 }
 
+static SkScaledBitmapSampler::RowProc get_gray_to_4444_proc(const SkImageDecoder& decoder) {
+    // Skip zeroes and unpremul make no difference
+    if (decoder.getDitherImage()) {
+        return Sample_Gray_D4444_D;
+    }
+    return Sample_Gray_D4444;
+}
+
 static bool Sample_RGBx_D4444(void* SK_RESTRICT dstRow,
                               const uint8_t* SK_RESTRICT src,
                               int width, int deltaSrc, int, const SkPMColor[]) {
@@ -162,6 +249,14 @@ static bool Sample_RGBx_D4444_D(void* SK_RESTRICT dstRow,
     return false;
 }
 
+static SkScaledBitmapSampler::RowProc get_RGBx_to_4444_proc(const SkImageDecoder& decoder) {
+    // Skip zeroes and unpremul make no difference
+    if (decoder.getDitherImage()) {
+        return Sample_RGBx_D4444_D;
+    }
+    return Sample_RGBx_D4444;
+}
+
 static bool Sample_RGBA_D4444(void* SK_RESTRICT dstRow,
                               const uint8_t* SK_RESTRICT src,
                               int width, int deltaSrc, int, const SkPMColor[]) {
@@ -178,9 +273,30 @@ static bool Sample_RGBA_D4444(void* SK_RESTRICT dstRow,
     return alphaMask != 0xFF;
 }
 
+static bool Sample_RGBA_D4444_SkipZ(void* SK_RESTRICT dstRow,
+                                    const uint8_t* SK_RESTRICT src,
+                                    int width, int deltaSrc, int,
+                                    const SkPMColor[]) {
+    SkPMColor16* SK_RESTRICT dst = (SkPMColor16*)dstRow;
+    unsigned alphaMask = 0xFF;
+
+    for (int x = 0; x < width; x++) {
+        unsigned alpha = src[3];
+        if (alpha != 0) {

[scroggo, 2013/09/19 18:43:43]

This function is the same as Sample_RGBA_D4444, except the calculation of c and
assigning to dst[x] are skipped if skip zeroes is requested when alpha == 0.

+            SkPMColor c = SkPreMultiplyARGB(alpha, src[0], src[1], src[2]);
+            dst[x] = SkPixel32ToPixel4444(c);
+        }
+        src += deltaSrc;
+        alphaMask &= alpha;
+    }
+    return alphaMask != 0xFF;
+}
+
+
 static bool Sample_RGBA_D4444_D(void* SK_RESTRICT dstRow,
                                 const uint8_t* SK_RESTRICT src,
-                            int width, int deltaSrc, int y, const SkPMColor[]) {
+                                int width, int deltaSrc, int y,
+                                const SkPMColor[]) {
     SkPMColor16* SK_RESTRICT dst = (SkPMColor16*)dstRow;
     unsigned alphaMask = 0xFF;
     DITHER_4444_SCAN(y);
@@ -195,6 +311,44 @@ static bool Sample_RGBA_D4444_D(void* SK_RESTRICT dstRow,
     return alphaMask != 0xFF;
 }
 
+static bool Sample_RGBA_D4444_D_SkipZ(void* SK_RESTRICT dstRow,
+                                      const uint8_t* SK_RESTRICT src,
+                                      int width, int deltaSrc, int y,
+                                      const SkPMColor[]) {
+    SkPMColor16* SK_RESTRICT dst = (SkPMColor16*)dstRow;
+    unsigned alphaMask = 0xFF;
+    DITHER_4444_SCAN(y);
+
+    for (int x = 0; x < width; x++) {
+        unsigned alpha = src[3];
+        if (alpha != 0) {

[scroggo, 2013/09/19 18:43:43]

Again, this function is the same as Sample_RGBA_D4444_D except if alpha is 0.

+            SkPMColor c = SkPreMultiplyARGB(alpha, src[0], src[1], src[2]);
+            dst[x] = SkDitherARGB32To4444(c, DITHER_VALUE(x));
+        }
+        src += deltaSrc;
+        alphaMask &= alpha;
+    }
+    return alphaMask != 0xFF;
+}
+
+static SkScaledBitmapSampler::RowProc get_RGBA_to_4444_proc(const SkImageDecoder& decoder) {
+    if (decoder.getRequireUnpremultipliedColors()) {
+        // Unpremultiplied is not supported for 4444
+        return NULL;
+    }
+    const bool dither = decoder.getDitherImage();
+    if (decoder.getSkipWritingZeroes()) {
+        if (dither) {
+            return Sample_RGBA_D4444_D_SkipZ;
+        }
+        return Sample_RGBA_D4444_SkipZ;
+    }
+    if (dither) {
+        return Sample_RGBA_D4444_D;
+    }
+    return Sample_RGBA_D4444;
+}
+
 // Index
 
 #define A32_MASK_IN_PLACE   (SkPMColor)(SK_A32_MASK << SK_A32_SHIFT)
@@ -214,6 +368,36 @@ static bool Sample_Index_D8888(void* SK_RESTRICT dstRow,
     return cc != A32_MASK_IN_PLACE;
 }
 
+static bool Sample_Index_D8888_SkipZ(void* SK_RESTRICT dstRow,
+                                     const uint8_t* SK_RESTRICT src,
+                                     int width, int deltaSrc, int,
+                                     const SkPMColor ctable[]) {
+
+    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) {

[scroggo, 2013/09/19 18:43:43]

Same as Sample_Index_D8888, except if there's a 0. In this case it's the color,
since it was already multiplied.

+            dst[x] = c;
+        }
+        src += deltaSrc;
+    }
+    return cc != A32_MASK_IN_PLACE;
+}
+
+static SkScaledBitmapSampler::RowProc get_index_to_8888_proc(const SkImageDecoder& decoder) {
+    if (decoder.getRequireUnpremultipliedColors()) {
+        // Unpremultiplied is not supported for an index source.
+        return NULL;
+    }
+    // Dither makes no difference
+    if (decoder.getSkipWritingZeroes()) {
+        return Sample_Index_D8888_SkipZ;
+    }
+    return Sample_Index_D8888;
+}
+
 static bool Sample_Index_D565(void* SK_RESTRICT dstRow,
                                const uint8_t* SK_RESTRICT src,
                        int width, int deltaSrc, int, const SkPMColor ctable[]) {
@@ -242,6 +426,14 @@ static bool Sample_Index_D565_D(void* SK_RESTRICT dstRow,
     return false;
 }
 
+static SkScaledBitmapSampler::RowProc get_index_to_565_proc(const SkImageDecoder& decoder) {
+    // Unpremultiplied and skip zeroes make no difference
+    if (decoder.getDitherImage()) {
+        return Sample_Index_D565_D;
+    }
+    return Sample_Index_D565;
+}
+
 static bool Sample_Index_D4444(void* SK_RESTRICT dstRow,
                                const uint8_t* SK_RESTRICT src, int width,
                                int deltaSrc, int y, const SkPMColor ctable[]) {
@@ -274,6 +466,60 @@ static bool Sample_Index_D4444_D(void* SK_RESTRICT dstRow,
     return cc != A32_MASK_IN_PLACE;
 }
 
+static bool Sample_Index_D4444_SkipZ(void* SK_RESTRICT dstRow,
+                                     const uint8_t* SK_RESTRICT src, int width,
+                                     int deltaSrc, int y, const SkPMColor ctable[]) {
+
+    SkPMColor16* SK_RESTRICT dst = (SkPMColor16*)dstRow;
+    SkPMColor cc = A32_MASK_IN_PLACE;
+    for (int x = 0; x < width; x++) {
+        SkPMColor c = ctable[*src];
+        cc &= c;
+        if (c != 0) {

[scroggo, 2013/09/19 18:43:43]

Sample_Index_D4444_D plus alpha check.

+            dst[x] = SkPixel32ToPixel4444(c);
+        }
+        src += deltaSrc;
+    }
+    return cc != A32_MASK_IN_PLACE;
+}
+
+static bool Sample_Index_D4444_D_SkipZ(void* SK_RESTRICT dstRow,
+                                       const uint8_t* SK_RESTRICT src, int width,
+                                       int deltaSrc, int y, const SkPMColor ctable[]) {
+
+    SkPMColor16* SK_RESTRICT dst = (SkPMColor16*)dstRow;
+    SkPMColor cc = A32_MASK_IN_PLACE;
+    DITHER_4444_SCAN(y);
+
+    for (int x = 0; x < width; x++) {
+        SkPMColor c = ctable[*src];
+        cc &= c;
+        if (c != 0) {

[scroggo, 2013/09/19 18:43:43]

Same as Sample_Index_D4444 plus alpha check.

+            dst[x] = SkDitherARGB32To4444(c, DITHER_VALUE(x));
+        }
+        src += deltaSrc;
+    }
+    return cc != A32_MASK_IN_PLACE;
+}
+
+static SkScaledBitmapSampler::RowProc get_index_to_4444_proc(const SkImageDecoder& decoder) {
+    // Unpremul not allowed
+    if (decoder.getRequireUnpremultipliedColors()) {
+        return NULL;
+    }
+    const bool dither = decoder.getDitherImage();
+    if (decoder.getSkipWritingZeroes()) {
+        if (dither) {
+            return Sample_Index_D4444_D_SkipZ;
+        }
+        return Sample_Index_D4444_SkipZ;
+    }
+    if (dither) {
+        return Sample_Index_D4444_D;
+    }
+    return Sample_Index_D4444;
+}
+
 static bool Sample_Index_DI(void* SK_RESTRICT dstRow,
                             const uint8_t* SK_RESTRICT src,
                             int width, int deltaSrc, int, const SkPMColor[]) {
@@ -289,6 +535,15 @@ static bool Sample_Index_DI(void* SK_RESTRICT dstRow,
     return false;
 }
 
+static SkScaledBitmapSampler::RowProc get_index_to_index_proc(const SkImageDecoder& decoder) {
+    // Unpremul not allowed
+    if (decoder.getRequireUnpremultipliedColors()) {
+        return NULL;
+    }
+    // Ignore dither and skip zeroes
+    return Sample_Index_DI;
+}
+
 // A8
 static bool Sample_Gray_DA8(void* SK_RESTRICT dstRow,
                             const uint8_t* SK_RESTRICT src,
@@ -298,41 +553,15 @@ static bool Sample_Gray_DA8(void* SK_RESTRICT dstRow,
     return true;
 }
 
-// 8888 Unpremul
-
-static bool Sample_Gray_D8888_Unpremul(void* SK_RESTRICT dstRow,

[scroggo, 2013/09/19 18:43:43]

This function was redundant, since we are not premultiplying an alpha of 0xFF

-                                       const uint8_t* SK_RESTRICT src,
-                                       int width, int deltaSrc, int,
-                                       const SkPMColor[]) {
-    uint32_t* SK_RESTRICT dst = reinterpret_cast<uint32_t*>(dstRow);
-    for (int x = 0; x < width; x++) {
-        dst[x] = SkPackARGB32NoCheck(0xFF, src[0], src[0], src[0]);
-        src += deltaSrc;
-    }
-    return false;
-}
-
-// Sample_RGBx_D8888_Unpremul is no different from Sample_RGBx_D8888, since alpha
-// is 0xFF
-
-static bool Sample_RGBA_D8888_Unpremul(void* SK_RESTRICT dstRow,

[scroggo, 2013/09/19 18:43:43]

Moved to be with the 8888 functions.

-                                       const uint8_t* SK_RESTRICT src,
-                                       int width, int deltaSrc, int,
-                                       const SkPMColor[]) {
-    uint32_t* SK_RESTRICT dst = reinterpret_cast<uint32_t*>(dstRow);
-    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;
+static SkScaledBitmapSampler::RowProc get_gray_to_A8_proc(const SkImageDecoder& decoder) {
+    if (decoder.getRequireUnpremultipliedColors()) {
+        return NULL;
     }
-    return alphaMask != 0xFF;
+    // Ignore skip and dither.
+    return Sample_Gray_DA8;
 }
 
-// Sample_Index_D8888_Unpremul is the same as Sample_Index_D8888, since the
-// color table has its colors inserted unpremultiplied.
-
+typedef SkScaledBitmapSampler::RowProc (*RowProcChooser)(const SkImageDecoder& decoder);
 ///////////////////////////////////////////////////////////////////////////////
 
 #include "SkScaledBitmapSampler.h"
@@ -377,58 +606,49 @@ SkScaledBitmapSampler::SkScaledBitmapSampler(int width, int height,
     SkASSERT(fDY > 0 && (fY0 + fDY * (fScaledHeight - 1)) < height);
 }
 
-bool SkScaledBitmapSampler::begin(SkBitmap* dst, SrcConfig sc, bool dither,
-                                  const SkPMColor ctable[],
-                                  bool requireUnpremul) {
-    static const RowProc gProcs[] = {
-        // 8888 (no dither distinction)
-        Sample_Gray_D8888,              Sample_Gray_D8888,
-        Sample_RGBx_D8888,              Sample_RGBx_D8888,
-        Sample_RGBA_D8888,              Sample_RGBA_D8888,
-        Sample_Index_D8888,             Sample_Index_D8888,
-        NULL,                           NULL,
-        // 565 (no alpha distinction)
-        Sample_Gray_D565,               Sample_Gray_D565_D,
-        Sample_RGBx_D565,               Sample_RGBx_D565_D,
-        Sample_RGBx_D565,               Sample_RGBx_D565_D,
-        Sample_Index_D565,              Sample_Index_D565_D,
-        Sample_D565_D565,               Sample_D565_D565,
-        // 4444
-        Sample_Gray_D4444,              Sample_Gray_D4444_D,
-        Sample_RGBx_D4444,              Sample_RGBx_D4444_D,
-        Sample_RGBA_D4444,              Sample_RGBA_D4444_D,
-        Sample_Index_D4444,             Sample_Index_D4444_D,
-        NULL,                           NULL,
-        // Index8
-        NULL,                           NULL,
-        NULL,                           NULL,
-        NULL,                           NULL,
-        Sample_Index_DI,                Sample_Index_DI,
-        NULL,                           NULL,
-        // A8
-        Sample_Gray_DA8,                Sample_Gray_DA8,
-        NULL,                           NULL,
-        NULL,                           NULL,
-        NULL,                           NULL,
-        NULL,                           NULL,
-        // 8888 Unpremul (no dither distinction)
-        Sample_Gray_D8888_Unpremul,     Sample_Gray_D8888_Unpremul,
-        Sample_RGBx_D8888,              Sample_RGBx_D8888,
-        Sample_RGBA_D8888_Unpremul,     Sample_RGBA_D8888_Unpremul,
-        Sample_Index_D8888,             Sample_Index_D8888,
-        NULL,                           NULL,
+bool SkScaledBitmapSampler::begin(SkBitmap* dst, SrcConfig sc,
+                                  const SkImageDecoder& decoder,
+                                  const SkPMColor ctable[]) {
+    static const RowProcChooser gProcChoosers[] = {
+        get_gray_to_8888_proc,
+        get_RGBx_to_8888_proc,
+        get_RGBA_to_8888_proc,
+        get_index_to_8888_proc,
+        NULL, // 565 to 8888
+
+        get_gray_to_565_proc,
+        get_RGBx_to_565_proc,
+        get_RGBx_to_565_proc, // The source alpha will be ignored.
+        get_index_to_565_proc,
+        get_565_to_565_proc,
+
+        get_gray_to_4444_proc,
+        get_RGBx_to_4444_proc,
+        get_RGBA_to_4444_proc,
+        get_index_to_4444_proc,
+        NULL, // 565 to 4444
+
+        NULL, // gray to index
+        NULL, // rgbx to index
+        NULL, // rgba to index
+        get_index_to_index_proc,
+        NULL, // 565 to index
+
+        get_gray_to_A8_proc,
+        NULL, // rgbx to a8
+        NULL, // rgba to a8
+        NULL, // index to a8
+        NULL, // 565 to a8
     };
+
     // The jump between dst configs in the table
-    static const int gProcDstConfigSpan = 10;
-    SK_COMPILE_ASSERT(SK_ARRAY_COUNT(gProcs) == 6 * gProcDstConfigSpan,
+    static const int gProcDstConfigSpan = 5;
+    SK_COMPILE_ASSERT(SK_ARRAY_COUNT(gProcChoosers) == 5 * gProcDstConfigSpan,
                       gProcs_has_the_wrong_number_of_entries);
 
     fCTable = ctable;
 
     int index = 0;
-    if (dither) {
-        index += 1;
-    }
     switch (sc) {
         case SkScaledBitmapSampler::kGray:
             fSrcPixelSize = 1;
@@ -436,23 +656,23 @@ bool SkScaledBitmapSampler::begin(SkBitmap* dst, SrcConfig sc, bool dither,
             break;
         case SkScaledBitmapSampler::kRGB:
             fSrcPixelSize = 3;
-            index += 2;
+            index += 1;
             break;
         case SkScaledBitmapSampler::kRGBX:
             fSrcPixelSize = 4;
-            index += 2;
+            index += 1;
             break;
         case SkScaledBitmapSampler::kRGBA:
             fSrcPixelSize = 4;
-            index += 4;
+            index += 2;
             break;
         case SkScaledBitmapSampler::kIndex:
             fSrcPixelSize = 1;
-            index += 6;
+            index += 3;
             break;
         case SkScaledBitmapSampler::kRGB_565:
             fSrcPixelSize = 2;
-            index += 8;
+            index += 4;
             break;
         default:
             return false;
@@ -478,14 +698,12 @@ bool SkScaledBitmapSampler::begin(SkBitmap* dst, SrcConfig sc, bool dither,
             return false;
     }
 
-    if (requireUnpremul) {
-        if (dst->config() != SkBitmap::kARGB_8888_Config) {
-            return false;
-        }
-        index += 5 * gProcDstConfigSpan;
+    RowProcChooser chooser = gProcChoosers[index];
+    if (NULL == chooser) {
+        fRowProc = NULL;
+    } else {
+        fRowProc = chooser(decoder);
     }
-
-    fRowProc = gProcs[index];
     fDstRow = (char*)dst->getPixels();
     fDstRowBytes = dst->rowBytes();
     fCurrY = 0;
@@ -501,3 +719,102 @@ bool SkScaledBitmapSampler::next(const uint8_t* SK_RESTRICT src) {
     fCurrY += 1;
     return hadAlpha;
 }
+
+#ifdef SK_DEBUG

[scroggo, 2013/09/19 18:43:43]

This is all part of a regression test. If desired, I can check in a version of
the test separately first, so we can see what changed.

+// The following code is for a test to ensure that changing the method to get the right row proc
+// did not change the row proc unintentionally. Tested by ImageDecodingTest.cpp
+
+// friend of SkScaledBitmapSampler solely for the purpose of accessing fRowProc.
+class RowProcTester {
+public:
+    static SkScaledBitmapSampler::RowProc getRowProc(const SkScaledBitmapSampler& sampler) {
+        return sampler.fRowProc;
+    }
+};
+
+
+// Table showing the expected RowProc for each combination of inputs.
+// Table formated as follows:
+// Each group of 5 consecutive rows represents sampling from a single
+// SkScaledBitmapSampler::SrcConfig.
+// Within each set, each row represents a different destination SkBitmap::Config
+// Each column represents a different combination of dither and unpremul.
+// D = dither   ~D = no dither
+// U = unpremul ~U = no unpremul
+//  ~D~U                D~U                     ~DU                         DU
+SkScaledBitmapSampler::RowProc gTestProcs[] = {
+    // Gray
+    Sample_Gray_DA8,    Sample_Gray_DA8,        NULL,                       NULL,                       // to A8
+    NULL,               NULL,                   NULL,                       NULL,                       // to Index8
+    Sample_Gray_D565,   Sample_Gray_D565_D,     Sample_Gray_D565,           Sample_Gray_D565_D,         // to 565
+    Sample_Gray_D4444,  Sample_Gray_D4444_D,    Sample_Gray_D4444,          Sample_Gray_D4444_D,        // to 4444
+    Sample_Gray_D8888,  Sample_Gray_D8888,      Sample_Gray_D8888,          Sample_Gray_D8888,          // to 8888
+    // Index
+    NULL,               NULL,                   NULL,                       NULL,                       // to A8
+    Sample_Index_DI,    Sample_Index_DI,        NULL,                       NULL,                       // to Index8
+    Sample_Index_D565,  Sample_Index_D565_D,    Sample_Index_D565,          Sample_Index_D565_D,        // to 565
+    Sample_Index_D4444, Sample_Index_D4444_D,   NULL,                       NULL,                       // to 4444
+    Sample_Index_D8888, Sample_Index_D8888,     NULL,                       NULL,                       // to 8888
+    // RGB
+    NULL,               NULL,                   NULL,                       NULL,                       // to A8
+    NULL,               NULL,                   NULL,                       NULL,                       // to Index8
+    Sample_RGBx_D565,   Sample_RGBx_D565_D,     Sample_RGBx_D565,           Sample_RGBx_D565_D,         // to 565
+    Sample_RGBx_D4444,  Sample_RGBx_D4444_D,    Sample_RGBx_D4444,          Sample_RGBx_D4444_D,        // to 4444
+    Sample_RGBx_D8888,  Sample_RGBx_D8888,      Sample_RGBx_D8888,          Sample_RGBx_D8888,          // to 8888
+    // RGBx is the same as RGB
+    NULL,               NULL,                   NULL,                       NULL,                       // to A8
+    NULL,               NULL,                   NULL,                       NULL,                       // to Index8
+    Sample_RGBx_D565,   Sample_RGBx_D565_D,     Sample_RGBx_D565,           Sample_RGBx_D565_D,         // to 565
+    Sample_RGBx_D4444,  Sample_RGBx_D4444_D,    Sample_RGBx_D4444,          Sample_RGBx_D4444_D,        // to 4444
+    Sample_RGBx_D8888,  Sample_RGBx_D8888,      Sample_RGBx_D8888,          Sample_RGBx_D8888,          // to 8888
+    // RGBA
+    NULL,               NULL,                   NULL,                       NULL,                       // to A8
+    NULL,               NULL,                   NULL,                       NULL,                       // to Index8
+    Sample_RGBx_D565,   Sample_RGBx_D565_D,     Sample_RGBx_D565,           Sample_RGBx_D565_D,         // to 565
+    Sample_RGBA_D4444,  Sample_RGBA_D4444_D,    NULL,                       NULL,                       // to 4444
+    Sample_RGBA_D8888,  Sample_RGBA_D8888,      Sample_RGBA_D8888_Unpremul, Sample_RGBA_D8888_Unpremul, // to 8888
+    // RGB_565
+    NULL,               NULL,                   NULL,                       NULL,                       // to A8
+    NULL,               NULL,                   NULL,                       NULL,                       // to Index8
+    Sample_D565_D565,   Sample_D565_D565,       Sample_D565_D565,           Sample_D565_D565,           // to 565
+    NULL,               NULL,                   NULL,                       NULL,                       // to 4444
+    NULL,               NULL,                   NULL,                       NULL,                       // to 8888
+};
+
+// Dummy class that allows instantiation of an ImageDecoder, so begin can query its fields.
+class DummyDecoder : public SkImageDecoder {
+public:
+    DummyDecoder() {}
+protected:
+    virtual bool onDecode(SkStream*, SkBitmap*, SkImageDecoder::Mode) SK_OVERRIDE {
+        return false;
+    }
+};
+
+void test_row_proc_choice() {
+    SkBitmap dummyBitmap;
+    DummyDecoder dummyDecoder;
+    size_t procCounter = 0;
+    for (int sc = SkScaledBitmapSampler::kGray; sc <= SkScaledBitmapSampler::kRGB_565; ++sc) {
+        for (int c = SkBitmap::kA8_Config; c <= SkBitmap::kARGB_8888_Config; ++c) {
+            for (int unpremul = 0; unpremul <= 1; ++unpremul) {
+                for (int dither = 0; dither <= 1; ++dither) {
+                    // Arbitrary width/height/sampleSize to allow SkScaledBitmapSampler to
+                    // be considered valid.
+                    SkScaledBitmapSampler sampler(10, 10, 1);
+                    dummyBitmap.setConfig((SkBitmap::Config) c, 10, 10);
+                    dummyDecoder.setDitherImage(SkToBool(dither));
+                    dummyDecoder.setRequireUnpremultipliedColors(SkToBool(unpremul));
+                    sampler.begin(&dummyBitmap, (SkScaledBitmapSampler::SrcConfig) sc,
+                                  dummyDecoder);
+                    SkScaledBitmapSampler::RowProc expected = gTestProcs[procCounter];
+                    SkScaledBitmapSampler::RowProc actual = RowProcTester::getRowProc(sampler);
+                    SkASSERT(expected == actual);
+                    procCounter++;
+                }
+            }
+        }
+    }
+    SkASSERT(SK_ARRAY_COUNT(gTestProcs) == procCounter);
+}
+#endif // SK_DEBUG