Add subsetting to SkScaledCodec

src/codec/SkMaskSwizzler.cpp

Index: src/codec/SkMaskSwizzler.cpp
diff --git a/src/codec/SkMaskSwizzler.cpp b/src/codec/SkMaskSwizzler.cpp
index 6ca9b58f4ed7e16e27490188aa6077412c1ed6dc..46f7898b1ffb3509000ddddc52618deb805714b5 100644
--- a/src/codec/SkMaskSwizzler.cpp
+++ b/src/codec/SkMaskSwizzler.cpp
@@ -250,9 +250,9 @@ static SkSwizzler::ResultAlpha swizzle_mask32_to_565(
  * Create a new mask swizzler
  *
  */
-SkMaskSwizzler* SkMaskSwizzler::CreateMaskSwizzler(
-        const SkImageInfo& dstInfo, const SkImageInfo& srcInfo, SkMasks* masks,
-        uint32_t bitsPerPixel) {
+SkMaskSwizzler* SkMaskSwizzler::CreateMaskSwizzler(const SkImageInfo& dstInfo,
+        const SkImageInfo& srcInfo, SkMasks* masks, uint32_t bitsPerPixel, int subsetLeft,
+        int subsetWidth) {
 
     // Choose the appropriate row procedure
     RowProc proc = nullptr;
@@ -354,9 +354,10 @@ SkMaskSwizzler* SkMaskSwizzler::CreateMaskSwizzler(
 
     // Get the sample size
     int sampleX;
-    SkScaledCodec::ComputeSampleSize(dstInfo, srcInfo, &sampleX, NULL);
+    SkScaledCodec::ComputeSampleSize(dstInfo.dimensions(), srcInfo.dimensions(), &sampleX, nullptr);
+    int startX = get_start_coord(sampleX) + subsetLeft;
 
-    return new SkMaskSwizzler(dstInfo, masks, proc, sampleX);
+    return new SkMaskSwizzler(masks, proc, subsetWidth, sampleX, startX);
 }
 
 /*
@@ -364,13 +365,13 @@ SkMaskSwizzler* SkMaskSwizzler::CreateMaskSwizzler(
  * Constructor for mask swizzler
  *
  */
-SkMaskSwizzler::SkMaskSwizzler(const SkImageInfo& dstInfo, SkMasks* masks,
-                               RowProc proc, uint32_t sampleX)
-    : fDstInfo(dstInfo)
-    , fMasks(masks)
+SkMaskSwizzler::SkMaskSwizzler(SkMasks* masks, RowProc proc, uint32_t width, uint32_t sampleX,
+        uint32_t startX)
+    : fMasks(masks)
     , fRowProc(proc)
+    , fWidth(width)
     , fSampleX(sampleX)
-    , fStartX(get_start_coord(sampleX))
+    , fStartX(startX)
 {}
 
 /*
@@ -380,5 +381,5 @@ SkMaskSwizzler::SkMaskSwizzler(const SkImageInfo& dstInfo, SkMasks* masks,
  */
 SkSwizzler::ResultAlpha SkMaskSwizzler::swizzle(void* dst, const uint8_t* SK_RESTRICT src) {
     SkASSERT(nullptr != dst && nullptr != src);
-    return fRowProc(dst, src, fDstInfo.width(), fMasks, fStartX, fSampleX);
+    return fRowProc(dst, src, fWidth, fMasks, fStartX, fSampleX);
 }