SkCodec::Result SkGifCodec::ReadUpToFirstImage(GifFileType* gif, uint32_t* transIndex) {
// Use this as a container to hold information about any gif extension
// blocks. This generally stores transparency and animation instructions.
SavedImage saveExt;
SkAutoTCallVProc<SavedImage, FreeExtension> autoFreeExt(&saveExt);
saveExt.ExtensionBlocks = nullptr;
saveExt.ExtensionBlockCount = 0;
GifByteType* extData;
int32_t extFunction;
// We will loop over components of gif images until we find an image. Once
// we find an image, we will decode and return it. While many gif files
// contain more than one image, we will simply decode the first image.
GifRecordType recordType;
do {
// Get the current record type
if (GIF_ERROR == DGifGetRecordType(gif, &recordType)) {
return gif_error("DGifGetRecordType failed.\n", kInvalidInput);
}
switch (recordType) {
case IMAGE_DESC_RECORD_TYPE: {
*transIndex = find_trans_index(saveExt);
// FIXME: Gif files may have multiple images stored in a single
// file. This is most commonly used to enable
// animations. Since we are leaving animated gifs as a
// TODO, we will return kSuccess after decoding the
// first image in the file. This is the same behavior
// as SkImageDecoder_libgif.
//
// Most times this works pretty well, but sometimes it
// doesn't. For example, I have an animated test image
// where the first image in the file is 1x1, but the
// subsequent images are meaningful. This currently
// displays the 1x1 image, which is not ideal. Right
// now I am leaving this as an issue that will be
// addressed when we implement animated gifs.
//
// It is also possible (not explicitly disallowed in the
// specification) that gif files provide multiple
// images in a single file that are all meant to be
// displayed in the same frame together. I will
// currently leave this unimplemented until I find a
// test case that expects this behavior.
return kSuccess;
}
// Extensions are used to specify special properties of the image
// such as transparency or animation.
case EXTENSION_RECORD_TYPE:
// Read extension data
if (GIF_ERROR == DGifGetExtension(gif, &extFunction, &extData)) {
return gif_error("Could not get extension.\n", kIncompleteInput);
}
// Create an extension block with our data
while (nullptr != extData) {
// Add a single block
#if GIFLIB_MAJOR < 5
if (AddExtensionBlock(&saveExt, extData[0],
&extData[1]) == GIF_ERROR) {
#else
if (GIF_ERROR == GifAddExtensionBlock(&saveExt.ExtensionBlockCount,
&saveExt.ExtensionBlocks,
extFunction, extData[0], &extData[1])) {
#endif
return gif_error("Could not add extension block.\n", kIncompleteInput);
}
// Move to the next block
if (GIF_ERROR == DGifGetExtensionNext(gif, &extData)) {
return gif_error("Could not get next extension.\n", kIncompleteInput);
}
}
break;
// Signals the end of the gif file
case TERMINATE_RECORD_TYPE:
break;
default:
// DGifGetRecordType returns an error if the record type does
// not match one of the above cases. This should not be
// reached.
SkASSERT(false);
break;
}
} while (TERMINATE_RECORD_TYPE != recordType);
return gif_error("Could not find any images to decode in gif file.\n", kInvalidInput);
}
bool SkGifCodec::GetDimensions(GifFileType* gif, SkISize* size, SkIRect* frameRect) {
// Get the encoded dimension values
SavedImage* image = &gif->SavedImages[gif->ImageCount - 1];
const GifImageDesc& desc = image->ImageDesc;
int frameLeft = desc.Left;
int frameTop = desc.Top;
int frameWidth = desc.Width;
int frameHeight = desc.Height;
int width = gif->SWidth;
int height = gif->SHeight;
// Ensure that the decode dimensions are large enough to contain the frame
width = SkTMax(width, frameWidth + frameLeft);
height = SkTMax(height, frameHeight + frameTop);
// All of these dimensions should be positive, as they are encoded as unsigned 16-bit integers.
// It is unclear why giflib casts them to ints. We will go ahead and check that they are
// in fact positive.
if (frameLeft < 0 || frameTop < 0 || frameWidth < 0 || frameHeight < 0 || width <= 0 ||
height <= 0) {
return false;
}
frameRect->setXYWH(frameLeft, frameTop, frameWidth, frameHeight);
size->set(width, height);
return true;
}
SkCodec::Result SkGifCodec::ReadUpToFirstImage(GifFileType* gif, uint32_t* transIndex) {
// Use this as a container to hold information about any gif extension
// blocks. This generally stores transparency and animation instructions.
SavedImage saveExt;
SkAutoTCallVProc<SavedImage, FreeExtension> autoFreeExt(&saveExt);
saveExt.ExtensionBlocks = nullptr;
saveExt.ExtensionBlockCount = 0;
GifByteType* extData;
int32_t extFunction;
// We will loop over components of gif images until we find an image. Once
// we find an image, we will decode and return it. While many gif files
// contain more than one image, we will simply decode the first image.
GifRecordType recordType;
do {
// Get the current record type
if (GIF_ERROR == DGifGetRecordType(gif, &recordType)) {
return gif_error("DGifGetRecordType failed.\n", kInvalidInput);
}
switch (recordType) {
case IMAGE_DESC_RECORD_TYPE: {
*transIndex = find_trans_index(saveExt);
// FIXME: Gif files may have multiple images stored in a single
// file. This is most commonly used to enable
// animations. Since we are leaving animated gifs as a
// TODO, we will return kSuccess after decoding the
// first image in the file. This is the same behavior
// as SkImageDecoder_libgif.
//
// Most times this works pretty well, but sometimes it
// doesn't. For example, I have an animated test image
// where the first image in the file is 1x1, but the
// subsequent images are meaningful. This currently
// displays the 1x1 image, which is not ideal. Right
// now I am leaving this as an issue that will be
// addressed when we implement animated gifs.
//
// It is also possible (not explicitly disallowed in the
// specification) that gif files provide multiple
// images in a single file that are all meant to be
// displayed in the same frame together. I will
// currently leave this unimplemented until I find a
// test case that expects this behavior.
return kSuccess;
}
// Extensions are used to specify special properties of the image
// such as transparency or animation.
case EXTENSION_RECORD_TYPE:
// Read extension data
if (GIF_ERROR == DGifGetExtension(gif, &extFunction, &extData)) {
return gif_error("Could not get extension.\n", kIncompleteInput);
}
// Create an extension block with our data
while (nullptr != extData) {
// Add a single block
if (GIF_ERROR == GifAddExtensionBlock(&saveExt.ExtensionBlockCount,
&saveExt.ExtensionBlocks,
extFunction, extData[0], &extData[1]))
{
return gif_error("Could not add extension block.\n", kIncompleteInput);
}
// Move to the next block
if (GIF_ERROR == DGifGetExtensionNext(gif, &extData)) {
return gif_error("Could not get next extension.\n", kIncompleteInput);
}
}
break;
// Signals the end of the gif file
case TERMINATE_RECORD_TYPE:
break;
default:
// DGifGetRecordType returns an error if the record type does
// not match one of the above cases. This should not be
// reached.
SkASSERT(false);
break;
}
} while (TERMINATE_RECORD_TYPE != recordType);
return gif_error("Could not find any images to decode in gif file.\n", kInvalidInput);
}
