/*
* Copyright 2015 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "SkCodec_libgif.h"
#include "SkCodecPriv.h"
#include "SkColorPriv.h"
#include "SkColorTable.h"
#include "SkGifInterlaceIter.h"
#include "SkStream.h"
#include "SkSwizzler.h"
#include "SkUtils.h"
/*
* Checks the start of the stream to see if the image is a gif
*/
bool SkGifCodec::IsGif(SkStream* stream) {
char buf[GIF_STAMP_LEN];
if (stream->read(buf, GIF_STAMP_LEN) == GIF_STAMP_LEN) {
if (memcmp(GIF_STAMP, buf, GIF_STAMP_LEN) == 0 ||
memcmp(GIF87_STAMP, buf, GIF_STAMP_LEN) == 0 ||
memcmp(GIF89_STAMP, buf, GIF_STAMP_LEN) == 0) {
return true;
}
}
return false;
}
/*
* Warning reporting function
*/
static void gif_warning(const char* msg) {
SkCodecPrintf("Gif Warning: %s\n", msg);
}
/*
* Error function
*/
static SkCodec::Result gif_error(const char* msg,
SkCodec::Result result = SkCodec::kInvalidInput) {
SkCodecPrintf("Gif Error: %s\n", msg);
return result;
}
/*
* Read function that will be passed to gif_lib
*/
static int32_t read_bytes_callback(GifFileType* fileType, GifByteType* out,
int32_t size) {
SkStream* stream = (SkStream*) fileType->UserData;
return (int32_t) stream->read(out, size);
}
/*
* Open the gif file
*/
static GifFileType* open_gif(SkStream* stream) {
#if GIFLIB_MAJOR < 5
return DGifOpen(stream, read_bytes_callback);
#else
return DGifOpen(stream, read_bytes_callback, NULL);
#endif
}
/*
* This function cleans up the gif object after the decode completes
* It is used in a SkAutoTCallIProc template
*/
void SkGifCodec::CloseGif(GifFileType* gif) {
#if GIFLIB_MAJOR < 5 || (GIFLIB_MAJOR == 5 && GIFLIB_MINOR == 0)
DGifCloseFile(gif);
#else
DGifCloseFile(gif, NULL);
#endif
}
/*
* This function free extension data that has been saved to assist the image
* decoder
*/
void SkGifCodec::FreeExtension(SavedImage* image) {
if (NULL != image->ExtensionBlocks) {
#if GIFLIB_MAJOR < 5
FreeExtension(image);
#else
GifFreeExtensions(&image->ExtensionBlockCount, &image->ExtensionBlocks);
#endif
}
}
/*
* Check if a there is an index of the color table for a transparent pixel
*/
static uint32_t find_trans_index(const SavedImage& image) {
// If there is a transparent index specified, it will be contained in an
// extension block. We will loop through extension blocks in reverse order
// to check the most recent extension blocks first.
for (int32_t i = image.ExtensionBlockCount - 1; i >= 0; i--) {
// Get an extension block
const ExtensionBlock& extBlock = image.ExtensionBlocks[i];
// Specifically, we need to check for a graphics control extension,
// which may contain transparency information. Also, note that a valid
// graphics control extension is always four bytes. The fourth byte
// is the transparent index (if it exists), so we need at least four
// bytes.
if (GRAPHICS_EXT_FUNC_CODE == extBlock.Function &&
extBlock.ByteCount >= 4) {
// Check the transparent color flag which indicates whether a
// transparent index exists. It is the least significant bit of
// the first byte of the extension block.
if (1 == (extBlock.Bytes[0] & 1)) {
// Use uint32_t to prevent sign extending
return extBlock.Bytes[3];
}
// There should only be one graphics control extension for the image frame
break;
}
}
// Use maximum unsigned int (surely an invalid index) to indicate that a valid
// index was not found.
return SK_MaxU32;
}
/*
* 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 NULL,
* codecOut will be set to a new SkGifCodec.
*
* @param gifOut
* If it returned true, and codecOut was NULL,
* gifOut must be non-NULL 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 (NULL == gif) {
gif_error("DGifOpen failed.\n");
return false;
}
if (NULL != codecOut) {
// Get fields from header
const int32_t width = gif->SWidth;
const int32_t height = gif->SHeight;
if (width <= 0 || height <= 0) {
gif_error("Invalid dimensions.\n");
return false;
}
// Return the codec
// kIndex is the most natural color type for gifs, so we set this as
// the default.
// Many gifs specify a color table index for transparent pixels. Every
// other pixel is guaranteed to be opaque. Despite this, because of the
// possiblity of transparent pixels, we cannot assume that the image is
// opaque. We have the option to set the alpha type as 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.
const SkImageInfo& imageInfo = SkImageInfo::Make(width, height,
kIndex_8_SkColorType, kPremul_SkAlphaType);
*codecOut = SkNEW_ARGS(SkGifCodec, (imageInfo, streamDeleter.detach(), gif.detach()));
} else {
SkASSERT(NULL != gifOut);
streamDeleter.detach();
*gifOut = gif.detach();
}
return true;
}
/*
* Assumes IsGif was called and returned true
* Creates a gif decoder
* Reads enough of the stream to determine the image format
*/
SkCodec* SkGifCodec::NewFromStream(SkStream* stream) {
SkCodec* codec = NULL;
if (ReadHeader(stream, &codec, NULL)) {
return codec;
}
return NULL;
}
SkGifCodec::SkGifCodec(const SkImageInfo& srcInfo, SkStream* stream,
GifFileType* gif)
: INHERITED(srcInfo, stream)
, fGif(gif)
{}
/*
* Checks if the conversion between the input image and the requested output
* image has been implemented
*/
static bool conversion_possible(const SkImageInfo& dst,
const SkImageInfo& src) {
// Ensure that the profile type is unchanged
if (dst.profileType() != src.profileType()) {
return false;
}
// Check for supported color and alpha types
switch (dst.colorType()) {
case kN32_SkColorType:
return kPremul_SkAlphaType == dst.alphaType() ||
kUnpremul_SkAlphaType == dst.alphaType();
case kIndex_8_SkColorType:
return kPremul_SkAlphaType == dst.alphaType() ||
kUnpremul_SkAlphaType == dst.alphaType();
default:
return false;
}
}
/*
* Initiates the gif decode
*/
SkCodec::Result SkGifCodec::onGetPixels(const SkImageInfo& dstInfo,
void* dst, size_t dstRowBytes,
const Options& opts,
SkPMColor* inputColorPtr,
int* inputColorCount) {
// Rewind if necessary
SkCodec::RewindState rewindState = this->rewindIfNeeded();
if (rewindState == kCouldNotRewind_RewindState) {
return kCouldNotRewind;
} else if (rewindState == kRewound_RewindState) {
GifFileType* gifOut = NULL;
if (!ReadHeader(this->stream(), NULL, &gifOut)) {
return kCouldNotRewind;
} else {
SkASSERT(NULL != gifOut);
fGif.reset(gifOut);
}
}
// Check for valid input parameters
if (dstInfo.dimensions() != this->getInfo().dimensions()) {
return gif_error("Scaling not supported.\n", kInvalidScale);
}
if (!conversion_possible(dstInfo, this->getInfo())) {
return gif_error("Cannot convert input type to output type.\n",
kInvalidConversion);
}
// 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 = NULL;
saveExt.ExtensionBlockCount = 0;
GifByteType* extData;
#if GIFLIB_MAJOR >= 5
int32_t extFunction;
#endif
// 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.
const int32_t width = dstInfo.width();
const int32_t height = dstInfo.height();
GifRecordType recordType;
do {
// Get the current record type
if (GIF_ERROR == DGifGetRecordType(fGif, &recordType)) {
return gif_error("DGifGetRecordType failed.\n", kInvalidInput);
}
switch (recordType) {
case IMAGE_DESC_RECORD_TYPE: {
// Read the image descriptor
if (GIF_ERROR == DGifGetImageDesc(fGif)) {
return gif_error("DGifGetImageDesc failed.\n",
kInvalidInput);
}
// If reading the image descriptor is successful, the image
// count will be incremented
SkASSERT(fGif->ImageCount >= 1);
SavedImage* image = &fGif->SavedImages[fGif->ImageCount - 1];
// Process the descriptor
const GifImageDesc& desc = image->ImageDesc;
int32_t imageLeft = desc.Left;
int32_t imageTop = desc.Top;
int32_t innerWidth = desc.Width;
int32_t innerHeight = desc.Height;
// Fail on non-positive dimensions
if (innerWidth <= 0 || innerHeight <= 0) {
return gif_error("Invalid dimensions for inner image.\n",
kInvalidInput);
}
// Treat the following cases as warnings and try to fix
if (innerWidth > width) {
gif_warning("Inner image too wide, shrinking.\n");
innerWidth = width;
imageLeft = 0;
} else if (imageLeft + innerWidth > width) {
gif_warning("Shifting inner image to left to fit.\n");
imageLeft = width - innerWidth;
} else if (imageLeft < 0) {
gif_warning("Shifting image to right to fit\n");
imageLeft = 0;
}
if (innerHeight > height) {
gif_warning("Inner image too tall, shrinking.\n");
innerHeight = height;
imageTop = 0;
} else if (imageTop + innerHeight > height) {
gif_warning("Shifting inner image up to fit.\n");
imageTop = height - innerHeight;
} else if (imageTop < 0) {
gif_warning("Shifting image down to fit\n");
imageTop = 0;
}
// Create a color table to store colors the giflib colorMap
SkPMColor alternateColorPtr[256];
SkPMColor* colorTable;
SkColorType dstColorType = dstInfo.colorType();
if (kIndex_8_SkColorType == dstColorType) {
SkASSERT(NULL != inputColorPtr);
SkASSERT(NULL != inputColorCount);
colorTable = inputColorPtr;
} else {
colorTable = alternateColorPtr;
}
// Set up the color table
uint32_t colorCount = 0;
// Allocate maximum storage to deal with invalid indices safely
const uint32_t maxColors = 256;
ColorMapObject* colorMap = fGif->Image.ColorMap;
// If there is no local color table, use the global color table
if (NULL == colorMap) {
colorMap = fGif->SColorMap;
}
if (NULL != colorMap) {
colorCount = colorMap->ColorCount;
SkASSERT(colorCount ==
(unsigned) (1 << (colorMap->BitsPerPixel)));
SkASSERT(colorCount <= 256);
for (uint32_t i = 0; i < colorCount; i++) {
colorTable[i] = SkPackARGB32(0xFF,
colorMap->Colors[i].Red,
colorMap->Colors[i].Green,
colorMap->Colors[i].Blue);
}
}
// This is used to fill unspecified pixels in the image data.
uint32_t fillIndex = fGif->SBackGroundColor;
ZeroInitialized zeroInit = opts.fZeroInitialized;
// Gifs have the option to specify the color at a single
// index of the color table as transparent.
{
// Get the transparent index. If the return value of this
// function is greater than the colorCount, we know that
// there is no valid transparent color in the color table.
// This occurs if there is no graphics control extension or
// if the index specified by the graphics control extension
// is out of range.
uint32_t transIndex = find_trans_index(saveExt);
if (transIndex < colorCount) {
colorTable[transIndex] = SK_ColorTRANSPARENT;
// If there is a transparent index, we also use this as
// the fill index.
fillIndex = transIndex;
} else if (fillIndex >= colorCount) {
// If the fill index is invalid, we default to 0. This
// behavior is unspecified but matches SkImageDecoder.
fillIndex = 0;
}
}
// Check if we can skip filling the background of the image. We
// may be able to if the memory is zero initialized.
bool skipBackground =
((kN32_SkColorType == dstColorType && colorTable[fillIndex] == 0) ||
(kIndex_8_SkColorType == dstColorType && fillIndex == 0)) &&
kYes_ZeroInitialized == zeroInit;
// Fill in the color table for indices greater than color count.
// This allows for predictable, safe behavior.
for (uint32_t i = colorCount; i < maxColors; i++) {
colorTable[i] = colorTable[fillIndex];
}
// Check if image is only a subset of the image frame
SkAutoTDelete<SkSwizzler> swizzler(NULL);
if (innerWidth < width || innerHeight < height) {
// Modify the destination info
const SkImageInfo subsetDstInfo =
dstInfo.makeWH(innerWidth, innerHeight);
// Fill the destination with the fill color
// FIXME: This may not be the behavior that we want for
// animated gifs where we draw on top of the
// previous frame.
if (!skipBackground) {
SkSwizzler::Fill(dst, dstInfo, dstRowBytes, height, fillIndex, colorTable);
}
// Modify the dst pointer
const int32_t dstBytesPerPixel =
SkColorTypeBytesPerPixel(dstColorType);
void* subsetDst = SkTAddOffset<void*>(dst,
dstRowBytes * imageTop +
dstBytesPerPixel * imageLeft);
// Create the subset swizzler
swizzler.reset(SkSwizzler::CreateSwizzler(
SkSwizzler::kIndex, colorTable, subsetDstInfo,
subsetDst, dstRowBytes, zeroInit));
} else {
// Create the fully dimensional swizzler
swizzler.reset(SkSwizzler::CreateSwizzler(
SkSwizzler::kIndex, colorTable, dstInfo, dst,
dstRowBytes, zeroInit));
}
// Stores output from dgiflib and input to the swizzler
SkAutoTDeleteArray<uint8_t>
buffer(SkNEW_ARRAY(uint8_t, innerWidth));
// Check the interlace flag and iterate over rows of the input
if (fGif->Image.Interlace) {
// In interlace mode, the rows of input are rearranged in
// the output image. We use an iterator to take care of
// the rearranging.
SkGifInterlaceIter iter(innerHeight);
for (int32_t y = 0; y < innerHeight; y++) {
if (GIF_ERROR == DGifGetLine(fGif, buffer.get(),
innerWidth)) {
// Recover from error by filling remainder of image
if (!skipBackground) {
memset(buffer.get(), fillIndex, innerWidth);
for (; y < innerHeight; y++) {
swizzler->next(buffer.get(), iter.nextY());
}
}
return gif_error(SkStringPrintf(
"Could not decode line %d of %d.\n",
y, height - 1).c_str(), kIncompleteInput);
}
swizzler->next(buffer.get(), iter.nextY());
}
} else {
// Standard mode
for (int32_t y = 0; y < innerHeight; y++) {
if (GIF_ERROR == DGifGetLine(fGif, buffer.get(),
innerWidth)) {
if (!skipBackground) {
SkSwizzler::Fill(swizzler->getDstRow(), dstInfo, dstRowBytes,
innerHeight - y, fillIndex, colorTable);
}
return gif_error(SkStringPrintf(
"Could not decode line %d of %d.\n",
y, height - 1).c_str(), kIncompleteInput);
}
swizzler->next(buffer.get());
}
}
// 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 GIFLIB_MAJOR < 5
if (GIF_ERROR ==
DGifGetExtension(fGif, &saveExt.Function, &extData)) {
#else
if (GIF_ERROR ==
DGifGetExtension(fGif, &extFunction, &extData)) {
#endif
return gif_error("Could not get extension.\n",
kIncompleteInput);
}
// Create an extension block with our data
while (NULL != extData) {
// Add a single block
#if GIFLIB_MAJOR < 5
if (GIF_ERROR == AddExtensionBlock(&saveExt, extData[0],
&extData[1])) {
#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(fGif, &extData)) {
return gif_error("Could not get next extension.\n",
kIncompleteInput);
}
#if GIFLIB_MAJOR < 5
saveExt.Function = 0;
#endif
}
break;
// Signals the end of the gif file
case TERMINATE_RECORD_TYPE:
break;
default:
// giflib returns an error code if the record type is not known.
// We should catch this error immediately.
SkASSERT(false);
break;
}
} while (TERMINATE_RECORD_TYPE != recordType);
return gif_error("Could not find any images to decode in gif file.\n",
kInvalidInput);
}