/*
* Read enough of the stream to initialize the SkGifCodec.
* Returns a bool representing success or failure.
*
* @param codecOut
* If it returned true, and codecOut was not nullptr,
* codecOut will be set to a new SkGifCodec.
*
* @param gifOut
* If it returned true, and codecOut was nullptr,
* gifOut must be non-nullptr and gifOut will be set to a new
* GifFileType pointer.
*
* @param stream
* Deleted on failure.
* codecOut will take ownership of it in the case where we created a codec.
* Ownership is unchanged when we returned a gifOut.
*
*/
bool SkGifCodec::ReadHeader(SkStream* stream, SkCodec** codecOut, GifFileType** gifOut) {
SkAutoTDelete<SkStream> streamDeleter(stream);
// Read gif header, logical screen descriptor, and global color table
SkAutoTCallVProc<GifFileType, CloseGif> gif(open_gif(stream));
if (nullptr == gif) {
gif_error("DGifOpen failed.\n");
return false;
}
// Read through gif extensions to get to the image data. Set the
// transparent index based on the extension data.
uint32_t transIndex;
SkCodec::Result result = ReadUpToFirstImage(gif, &transIndex);
if (kSuccess != result){
return false;
}
// Read the image descriptor
if (GIF_ERROR == DGifGetImageDesc(gif)) {
return false;
}
// If reading the image descriptor is successful, the image count will be
// incremented.
SkASSERT(gif->ImageCount >= 1);
if (nullptr != codecOut) {
SkISize size;
SkIRect frameRect;
if (!GetDimensions(gif, &size, &frameRect)) {
gif_error("Invalid gif size.\n");
return false;
}
bool frameIsSubset = (size != frameRect.size());
// Determine the encoded alpha type. The transIndex might be valid if it less
// than 256. We are not certain that the index is valid until we process the color
// table, since some gifs have color tables with less than 256 colors. If
// there might be a valid transparent index, we must indicate that the image has
// alpha.
// In the case where we must support alpha, we indicate kBinary, since every
// pixel will either be fully opaque or fully transparent.
SkEncodedInfo::Alpha alpha = (transIndex < 256) ? SkEncodedInfo::kBinary_Alpha :
SkEncodedInfo::kOpaque_Alpha;
// Return the codec
// Use kPalette since Gifs are encoded with a color table.
// Use 8-bits per component, since this is the output we get from giflib.
// FIXME: Gifs can actually be encoded with 4-bits per pixel. Can we support this?
SkEncodedInfo info = SkEncodedInfo::Make(SkEncodedInfo::kPalette_Color, alpha, 8);
*codecOut = new SkGifCodec(size.width(), size.height(), info, streamDeleter.release(),
gif.release(), transIndex, frameRect, frameIsSubset);
} else {
SkASSERT(nullptr != gifOut);
streamDeleter.release();
*gifOut = gif.release();
}
return true;
}
/*
* Read enough of the stream to initialize the SkGifCodec.
* Returns a bool representing success or failure.
*
* @param codecOut
* If it returned true, and codecOut was not nullptr,
* codecOut will be set to a new SkGifCodec.
*
* @param gifOut
* If it returned true, and codecOut was nullptr,
* gifOut must be non-nullptr and gifOut will be set to a new
* GifFileType pointer.
*
* @param stream
* Deleted on failure.
* codecOut will take ownership of it in the case where we created a codec.
* Ownership is unchanged when we returned a gifOut.
*
*/
bool SkGifCodec::ReadHeader(SkStream* stream, SkCodec** codecOut, GifFileType** gifOut) {
SkAutoTDelete<SkStream> streamDeleter(stream);
// Read gif header, logical screen descriptor, and global color table
SkAutoTCallVProc<GifFileType, CloseGif> gif(open_gif(stream));
if (nullptr == gif) {
gif_error("DGifOpen failed.\n");
return false;
}
// Read through gif extensions to get to the image data. Set the
// transparent index based on the extension data.
uint32_t transIndex;
SkCodec::Result result = ReadUpToFirstImage(gif, &transIndex);
if (kSuccess != result){
return false;
}
// Read the image descriptor
if (GIF_ERROR == DGifGetImageDesc(gif)) {
return false;
}
// If reading the image descriptor is successful, the image count will be
// incremented.
SkASSERT(gif->ImageCount >= 1);
if (nullptr != codecOut) {
SkISize size;
SkIRect frameRect;
if (!GetDimensions(gif, &size, &frameRect)) {
gif_error("Invalid gif size.\n");
return false;
}
bool frameIsSubset = (size != frameRect.size());
// Determine the recommended alpha type. The transIndex might be valid if it less
// than 256. We are not certain that the index is valid until we process the color
// table, since some gifs have color tables with less than 256 colors. If
// there might be a valid transparent index, we must indicate that the image has
// alpha.
// In the case where we must support alpha, we have the option to set the
// suggested alpha type to kPremul or kUnpremul. Both are valid since the alpha
// component will always be 0xFF or the entire 32-bit pixel will be set to zero.
// We prefer kPremul because we support kPremul, and it is more efficient to use
// kPremul directly even when kUnpremul is supported.
SkAlphaType alphaType = (transIndex < 256) ? kPremul_SkAlphaType : kOpaque_SkAlphaType;
// Return the codec
// kIndex is the most natural color type for gifs, so we set this as
// the default.
SkImageInfo imageInfo = SkImageInfo::Make(size.width(), size.height(), kIndex_8_SkColorType,
alphaType);
*codecOut = new SkGifCodec(imageInfo, streamDeleter.detach(), gif.detach(), transIndex,
frameRect, frameIsSubset);
} else {
SkASSERT(nullptr != gifOut);
streamDeleter.detach();
*gifOut = gif.detach();
}
return true;
}
