Add subsetting to SkScanlineDecoder

src/codec/SkCodec_libgif.cpp

Index: src/codec/SkCodec_libgif.cpp
diff --git a/src/codec/SkCodec_libgif.cpp b/src/codec/SkCodec_libgif.cpp
index 7bfbbf6ceb760b7b7d54dbd91084a2196bbb4f50..16b2eca874bf3b05a600a1c939992ef2053b04c9 100644
--- a/src/codec/SkCodec_libgif.cpp
+++ b/src/codec/SkCodec_libgif.cpp
@@ -100,7 +100,7 @@ static uint32_t find_trans_index(const SavedImage& image) {
  * It is used in a SkAutoTCallIProc template
  */
 void SkGifCodec::CloseGif(GifFileType* gif) {
-    DGifCloseFile(gif, NULL);
+    DGifCloseFile(gif, nullptr);
 }
 
 /*
@@ -108,7 +108,7 @@ void SkGifCodec::CloseGif(GifFileType* gif) {
  * decoder
  */
 void SkGifCodec::FreeExtension(SavedImage* image) {
-    if (NULL != image->ExtensionBlocks) {
+    if (nullptr != image->ExtensionBlocks) {
         GifFreeExtensions(&image->ExtensionBlockCount, &image->ExtensionBlocks);
     }
 }
@@ -221,8 +221,8 @@ SkGifCodec::SkGifCodec(const SkImageInfo& srcInfo, SkStream* stream, GifFileType
     , fFillIndex(0)
     , fFrameRect(frameRect)
     , fFrameIsSubset(frameIsSubset)
-    , fColorTable(NULL)
-    , fSwizzler(NULL)
+    , fColorTable(nullptr)
+    , fSwizzler(nullptr)
 {}
 
 bool SkGifCodec::onRewind() {
@@ -355,7 +355,7 @@ void SkGifCodec::initializeColorTable(const SkImageInfo& dstInfo, SkPMColor* inp
     // Set up our own color table
     const uint32_t maxColors = 256;
     SkPMColor colorPtr[256];
-    if (NULL != inputColorCount) {
+    if (nullptr != inputColorCount) {
         // We set the number of colors to maxColors in order to ensure
         // safe memory accesses.  Otherwise, an invalid pixel could
         // access memory outside of our color table array.
@@ -365,12 +365,12 @@ void SkGifCodec::initializeColorTable(const SkImageInfo& dstInfo, SkPMColor* inp
     // Get local color table
     ColorMapObject* colorMap = fGif->Image.ColorMap;
     // If there is no local color table, use the global color table
-    if (NULL == colorMap) {
+    if (nullptr == colorMap) {
         colorMap = fGif->SColorMap;
     }
 
     uint32_t colorCount = 0;
-    if (NULL != colorMap) {
+    if (nullptr != colorMap) {
         colorCount = colorMap->ColorCount;
         // giflib guarantees these properties
         SkASSERT(colorCount == (unsigned) (1 << (colorMap->BitsPerPixel)));
@@ -410,10 +410,6 @@ void SkGifCodec::initializeColorTable(const SkImageInfo& dstInfo, SkPMColor* inp
 SkCodec::Result SkGifCodec::prepareToDecode(const SkImageInfo& dstInfo, SkPMColor* inputColorPtr,
         int* inputColorCount, const Options& opts) {
     // Check for valid input parameters
-    if (opts.fSubset) {
-        // Subsets are not supported.
-        return kUnimplemented;
-    }
     if (!conversion_possible(dstInfo, this->getInfo())) {
         return gif_error("Cannot convert input type to output type.\n",
                 kInvalidConversion);
@@ -424,11 +420,9 @@ SkCodec::Result SkGifCodec::prepareToDecode(const SkImageInfo& dstInfo, SkPMColo
     return kSuccess;
 }
 
-SkCodec::Result SkGifCodec::initializeSwizzler(const SkImageInfo& dstInfo,
-        ZeroInitialized zeroInit) {
+SkCodec::Result SkGifCodec::initializeSwizzler(const SkImageInfo& dstInfo, const Options& opts) {
     const SkPMColor* colorPtr = get_color_ptr(fColorTable.get());
-    fSwizzler.reset(SkSwizzler::CreateSwizzler(SkSwizzler::kIndex,
-            colorPtr, dstInfo, zeroInit));
+    fSwizzler.reset(SkSwizzler::CreateSwizzler(SkSwizzler::kIndex, colorPtr, dstInfo, opts));
     if (nullptr != fSwizzler.get()) {
         return kSuccess;
     }
@@ -460,7 +454,7 @@ SkCodec::Result SkGifCodec::onGetPixels(const SkImageInfo& dstInfo,
     // Initialize the swizzler
     if (fFrameIsSubset) {
         const SkImageInfo subsetDstInfo = dstInfo.makeWH(fFrameRect.width(), fFrameRect.height());
-        if (kSuccess != this->initializeSwizzler(subsetDstInfo, opts.fZeroInitialized)) {
+        if (kSuccess != this->initializeSwizzler(subsetDstInfo, opts)) {
             return gif_error("Could not initialize swizzler.\n", kUnimplemented);
         }
 
@@ -474,7 +468,7 @@ SkCodec::Result SkGifCodec::onGetPixels(const SkImageInfo& dstInfo,
         dst = SkTAddOffset<void*>(dst, dstRowBytes * fFrameRect.top() +
                 dstBytesPerPixel * fFrameRect.left());
     } else {
-        if (kSuccess != this->initializeSwizzler(dstInfo, opts.fZeroInitialized)) {
+        if (kSuccess != this->initializeSwizzler(dstInfo, opts)) {
             return gif_error("Could not initialize swizzler.\n", kUnimplemented);
         }
     }
@@ -509,11 +503,11 @@ SkCodec::Result SkGifCodec::onStartScanlineDecode(const SkImageInfo& dstInfo,
     // Initialize the swizzler
     if (fFrameIsSubset) {
         const SkImageInfo subsetDstInfo = dstInfo.makeWH(fFrameRect.width(), fFrameRect.height());
-        if (kSuccess != this->initializeSwizzler(subsetDstInfo, opts.fZeroInitialized)) {
+        if (kSuccess != this->initializeSwizzler(subsetDstInfo, opts)) {
             return gif_error("Could not initialize swizzler.\n", kUnimplemented);
         }
     } else {
-        if (kSuccess != this->initializeSwizzler(dstInfo, opts.fZeroInitialized)) {
+        if (kSuccess != this->initializeSwizzler(dstInfo, opts)) {
             return gif_error("Could not initialize swizzler.\n", kUnimplemented);
         }
     }