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/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
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* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
* The Original Code is Mozilla Communicator client code.
* The Initial Developer of the Original Code is
* Netscape Communications Corporation.
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* Contributor(s):
* Alternatively, the contents of this file may be used under the terms of
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* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
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#ifndef SkGifImageReader_h
#define SkGifImageReader_h
// Define ourselves as the clientPtr. Mozilla just hacked their C++ callback class into this old C decoder,
// so we will too.
class SkGifCodec;
#include "include/codec/SkCodec.h"
#include "include/codec/SkCodecAnimation.h"
#include "include/core/SkData.h"
#include "include/core/SkImageInfo.h"
#include "include/private/SkTArray.h"
#include "src/codec/SkCodecPriv.h"
#include "src/codec/SkColorTable.h"
#include "src/codec/SkFrameHolder.h"
#include "src/codec/SkStreamBuffer.h"
#include <array>
#include <memory>
typedef SkTArray<unsigned char, true> SkGIFRow;
#define SK_MAX_COLORS 256
// List of possible parsing states.
enum SkGIFState {
class SkGIFFrameContext;
class SkGIFColorMap;
// LZW decoder state machine.
class SkGIFLZWContext final : public SkNoncopyable {
SkGIFLZWContext(SkGifCodec* client, const SkGIFFrameContext* frameContext)
: codesize(0)
, codemask(0)
, clearCode(0)
, avail(0)
, oldcode(0)
, bits(0)
, datum(0)
, ipass(0)
, irow(0)
, rowsRemaining(0)
, rowIter(nullptr)
, m_client(client)
, m_frameContext(frameContext)
{ }
bool prepareToDecode();
void outputRow(const unsigned char* rowBegin);
bool doLZW(const unsigned char* block, size_t bytesInBlock);
bool hasRemainingRows() { return SkToBool(rowsRemaining); }
// LZW decoding states and output states.
int codesize;
int codemask;
int clearCode; // Codeword used to trigger dictionary reset.
int avail; // Index of next available slot in dictionary.
int oldcode;
int bits; // Number of unread bits in "datum".
int datum; // 32-bit input buffer.
int ipass; // Interlace pass; Ranges 1-4 if interlaced.
size_t irow; // Current output row, starting at zero.
size_t rowsRemaining; // Rows remaining to be output.
unsigned short prefix[SK_MAX_DICTIONARY_ENTRIES];
std::array<std::array<unsigned char, SK_DICTIONARY_WORD_SIZE>,
unsigned short suffixLength[SK_MAX_DICTIONARY_ENTRIES];
SkGIFRow rowBuffer; // Single scanline temporary buffer.
unsigned char* rowIter;
SkGifCodec* const m_client;
const SkGIFFrameContext* m_frameContext;
struct SkGIFLZWBlock {
SkGIFLZWBlock(size_t position, size_t size)
: blockPosition(position), blockSize(size) {}
size_t blockPosition;
size_t blockSize;
class SkGIFColorMap final {
static constexpr int kNotFound = -1;
: m_isDefined(false)
, m_position(0)
, m_colors(0)
, m_transPixel(kNotFound)
, m_packColorProc(nullptr)
void setNumColors(int colors) {
m_colors = colors;
void setTablePosition(size_t position) {
m_position = position;
m_isDefined = true;
int numColors() const { return m_colors; }
bool isDefined() const { return m_isDefined; }
// Build RGBA table using the data stream.
sk_sp<SkColorTable> buildTable(SkStreamBuffer*, SkColorType dstColorType,
int transparentPixel) const;
bool m_isDefined;
size_t m_position;
int m_colors;
// Cached values. If these match on a new request, we can reuse m_table.
mutable int m_transPixel;
mutable PackColorProc m_packColorProc;
mutable sk_sp<SkColorTable> m_table;
class SkGifImageReader;
// LocalFrame output state machine.
class SkGIFFrameContext : public SkFrame {
SkGIFFrameContext(int id)
, m_transparentPixel(SkGIFColorMap::kNotFound)
, m_dataSize(0)
, m_progressiveDisplay(false)
, m_interlaced(false)
, m_currentLzwBlock(0)
, m_isComplete(false)
, m_isHeaderDefined(false)
, m_isDataSizeDefined(false)
~SkGIFFrameContext() override
void addLzwBlock(size_t position, size_t size)
m_lzwBlocks.emplace_back(position, size);
bool decode(SkStreamBuffer*, SkGifCodec* client, bool* frameDecoded);
int transparentPixel() const { return m_transparentPixel; }
void setTransparentPixel(int pixel) { m_transparentPixel = pixel; }
bool isComplete() const { return m_isComplete; }
void setComplete() { m_isComplete = true; }
bool isHeaderDefined() const { return m_isHeaderDefined; }
void setHeaderDefined() { m_isHeaderDefined = true; }
bool isDataSizeDefined() const { return m_isDataSizeDefined; }
int dataSize() const { return m_dataSize; }
void setDataSize(int size)
m_dataSize = size;
m_isDataSizeDefined = true;
bool progressiveDisplay() const { return m_progressiveDisplay; }
void setProgressiveDisplay(bool progressiveDisplay) { m_progressiveDisplay = progressiveDisplay; }
bool interlaced() const { return m_interlaced; }
void setInterlaced(bool interlaced) { m_interlaced = interlaced; }
void clearDecodeState() { m_lzwContext.reset(); }
const SkGIFColorMap& localColorMap() const { return m_localColorMap; }
SkGIFColorMap& localColorMap() { return m_localColorMap; }
SkEncodedInfo::Alpha onReportedAlpha() const override;
int m_transparentPixel; // Index of transparent pixel. Value is kNotFound if there is no transparent pixel.
int m_dataSize;
bool m_progressiveDisplay; // If true, do Haeberli interlace hack.
bool m_interlaced; // True, if scanlines arrive interlaced order.
std::unique_ptr<SkGIFLZWContext> m_lzwContext;
// LZW blocks for this frame.
SkTArray<SkGIFLZWBlock> m_lzwBlocks;
SkGIFColorMap m_localColorMap;
int m_currentLzwBlock;
bool m_isComplete;
bool m_isHeaderDefined;
bool m_isDataSizeDefined;
typedef SkFrame INHERITED;
class SkGifImageReader final : public SkFrameHolder {
// This takes ownership of stream.
SkGifImageReader(std::unique_ptr<SkStream> stream)
: m_client(nullptr)
, m_state(SkGIFType)
, m_bytesToConsume(6) // Number of bytes for GIF type, either "GIF87a" or "GIF89a".
, m_version(0)
, m_loopCount(cLoopCountNotSeen)
, m_streamBuffer(std::move(stream))
, m_parseCompleted(false)
, m_firstFrameHasAlpha(false)
~SkGifImageReader() override
void setClient(SkGifCodec* client) { m_client = client; }
// Option to pass to parse(). All enums are negative, because a non-negative value is used to
// indicate that the Reader should parse up to and including the frame indicated.
enum SkGIFParseQuery {
// Parse enough to determine the size. Note that this parses the first frame's header,
// since we may decide to expand based on the frame's dimensions.
SkGIFSizeQuery = -1,
// Parse to the end, so we know about all frames.
SkGIFFrameCountQuery = -2,
// Parse until we see the loop count.
SkGIFLoopCountQuery = -3,
// Parse incoming GIF data stream into internal data structures.
// Non-negative values are used to indicate to parse through that frame.
SkCodec::Result parse(SkGIFParseQuery);
// Decode the frame indicated by frameIndex.
// frameComplete will be set to true if the frame is completely decoded.
// The method returns false if there is an error.
bool decode(int frameIndex, bool* frameComplete);
int imagesCount() const
const int frames = m_frames.count();
if (!frames) {
return 0;
// This avoids counting an empty frame when the file is truncated (or
// simply not yet complete) after receiving SkGIFControlExtension (and
// possibly SkGIFImageHeader) but before reading the color table. This
// ensures that we do not count a frame before we know its required
// frame.
return m_frames.back()->reachedStartOfData() ? frames : frames - 1;
int loopCount() const {
if (cLoopCountNotSeen == m_loopCount) {
return 0;
return m_loopCount;
const SkGIFColorMap& globalColorMap() const
return m_globalColorMap;
const SkGIFFrameContext* frameContext(int index) const
return index >= 0 && index < m_frames.count()
? m_frames[index].get() : nullptr;
void clearDecodeState() {
for (int index = 0; index < m_frames.count(); index++) {
// Return the color table for frame index (which may be the global color table).
sk_sp<SkColorTable> getColorTable(SkColorType dstColorType, int index);
bool firstFrameHasAlpha() const { return m_firstFrameHasAlpha; }
const SkFrame* onGetFrame(int i) const override {
return static_cast<const SkFrame*>(this->frameContext(i));
// Requires that one byte has been buffered into m_streamBuffer.
unsigned char getOneByte() const {
return reinterpret_cast<const unsigned char*>(m_streamBuffer.get())[0];
void addFrameIfNecessary();
bool currentFrameIsFirstFrame() const
return m_frames.empty() || (m_frames.count() == 1 && !m_frames[0]->isComplete());
// Unowned pointer
SkGifCodec* m_client;
// Parsing state machine.
SkGIFState m_state; // Current decoder master state.
size_t m_bytesToConsume; // Number of bytes to consume for next stage of parsing.
// Global (multi-image) state.
int m_version; // Either 89 for GIF89 or 87 for GIF87.
SkGIFColorMap m_globalColorMap;
static constexpr int cLoopCountNotSeen = -2;
int m_loopCount; // Netscape specific extension block to control the number of animation loops a GIF renders.
SkTArray<std::unique_ptr<SkGIFFrameContext>> m_frames;
SkStreamBuffer m_streamBuffer;
bool m_parseCompleted;
// This value can be computed before we create a SkGIFFrameContext, so we
// store it here instead of on m_frames[0].
bool m_firstFrameHasAlpha;