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- /* -*- Mode: C; tab-width: 2; 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
- * the License. You may obtain a copy of the License at
- * http://www.mozilla.org/MPL/
- *
- * 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.org code.
- *
- * The Initial Developer of the Original Code is
- * Netscape Communications Corporation.
- * Portions created by the Initial Developer are Copyright (C) 1998
- * the Initial Developer. All Rights Reserved.
- *
- * Contributor(s):
- * Chris Saari <saari@netscape.com>
- * Apple Computer
- *
- * Alternatively, the contents of this file may be used under the terms of
- * either the GNU General Public License Version 2 or later (the "GPL"), or
- * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
- * in which case the provisions of the GPL or the LGPL are applicable instead
- * of those above. If you wish to allow use of your version of this file only
- * under the terms of either the GPL or the LGPL, and not to allow others to
- * use your version of this file under the terms of the MPL, indicate your
- * decision by deleting the provisions above and replace them with the notice
- * and other provisions required by the GPL or the LGPL. If you do not delete
- * the provisions above, a recipient may use your version of this file under
- * the terms of any one of the MPL, the GPL or the LGPL.
- *
- * ***** END LICENSE BLOCK ***** */
- /*
- The Graphics Interchange Format(c) is the copyright property of CompuServe
- Incorporated. Only CompuServe Incorporated is authorized to define, redefine,
- enhance, alter, modify or change in any way the definition of the format.
- CompuServe Incorporated hereby grants a limited, non-exclusive, royalty-free
- license for the use of the Graphics Interchange Format(sm) in computer
- software; computer software utilizing GIF(sm) must acknowledge ownership of the
- Graphics Interchange Format and its Service Mark by CompuServe Incorporated, in
- User and Technical Documentation. Computer software utilizing GIF, which is
- distributed or may be distributed without User or Technical Documentation must
- display to the screen or printer a message acknowledging ownership of the
- Graphics Interchange Format and the Service Mark by CompuServe Incorporated; in
- this case, the acknowledgement may be displayed in an opening screen or leading
- banner, or a closing screen or trailing banner. A message such as the following
- may be used:
- "The Graphics Interchange Format(c) is the Copyright property of
- CompuServe Incorporated. GIF(sm) is a Service Mark property of
- CompuServe Incorporated."
- For further information, please contact :
- CompuServe Incorporated
- Graphics Technology Department
- 5000 Arlington Center Boulevard
- Columbus, Ohio 43220
- U. S. A.
- CompuServe Incorporated maintains a mailing list with all those individuals and
- organizations who wish to receive copies of this document when it is corrected
- or revised. This service is offered free of charge; please provide us with your
- mailing address.
- */
- #include "include/core/SkColorPriv.h"
- #include "src/codec/SkGifCodec.h"
- #include "third_party/gif/SkGifImageReader.h"
- #include <algorithm>
- #include <string.h>
- // GETN(n, s) requests at least 'n' bytes available from 'q', at start of state 's'.
- //
- // Note, the hold will never need to be bigger than 256 bytes to gather up in the hold,
- // as each GIF block (except colormaps) can never be bigger than 256 bytes.
- // Colormaps are directly copied in the resp. global_colormap or dynamically allocated local_colormap.
- // So a fixed buffer in SkGifImageReader is good enough.
- // This buffer is only needed to copy left-over data from one GifWrite call to the next
- #define GETN(n, s) \
- do { \
- m_bytesToConsume = (n); \
- m_state = (s); \
- } while (0)
- // Get a 16-bit value stored in little-endian format.
- #define GETINT16(p) ((p)[1]<<8|(p)[0])
- namespace {
- bool is_palette_index_valid(int transparentIndex) {
- // -1 is a signal that there is no transparent index.
- // Otherwise, it is encoded in 8 bits, and all 256 values are considered
- // valid since a GIF may use an index outside of the palette to be
- // transparent.
- return transparentIndex >= 0;
- }
- } // anonymous namespace
- // Send the data to the display front-end.
- void SkGIFLZWContext::outputRow(const unsigned char* rowBegin)
- {
- int drowStart = irow;
- int drowEnd = irow;
- // Haeberli-inspired hack for interlaced GIFs: Replicate lines while
- // displaying to diminish the "venetian-blind" effect as the image is
- // loaded. Adjust pixel vertical positions to avoid the appearance of the
- // image crawling up the screen as successive passes are drawn.
- if (m_frameContext->progressiveDisplay() && m_frameContext->interlaced() && ipass < 4) {
- unsigned rowDup = 0;
- unsigned rowShift = 0;
- switch (ipass) {
- case 1:
- rowDup = 7;
- rowShift = 3;
- break;
- case 2:
- rowDup = 3;
- rowShift = 1;
- break;
- case 3:
- rowDup = 1;
- rowShift = 0;
- break;
- default:
- break;
- }
- drowStart -= rowShift;
- drowEnd = drowStart + rowDup;
- // Extend if bottom edge isn't covered because of the shift upward.
- if ((unsigned)((m_frameContext->height() - 1) - drowEnd) <= rowShift)
- drowEnd = m_frameContext->height() - 1;
- // Clamp first and last rows to upper and lower edge of image.
- if (drowStart < 0)
- drowStart = 0;
- if (drowEnd >= m_frameContext->height())
- drowEnd = m_frameContext->height() - 1;
- }
- // Protect against too much image data.
- if (drowStart >= m_frameContext->height())
- return;
- // CALLBACK: Let the client know we have decoded a row.
- const bool writeTransparentPixels =
- SkCodec::kNoFrame == m_frameContext->getRequiredFrame();
- m_client->haveDecodedRow(m_frameContext->frameId(), rowBegin,
- drowStart, drowEnd - drowStart + 1, writeTransparentPixels);
- if (!m_frameContext->interlaced())
- irow++;
- else {
- do {
- switch (ipass) {
- case 1:
- irow += 8;
- if (irow >= (unsigned) m_frameContext->height()) {
- ipass++;
- irow = 4;
- }
- break;
- case 2:
- irow += 8;
- if (irow >= (unsigned) m_frameContext->height()) {
- ipass++;
- irow = 2;
- }
- break;
- case 3:
- irow += 4;
- if (irow >= (unsigned) m_frameContext->height()) {
- ipass++;
- irow = 1;
- }
- break;
- case 4:
- irow += 2;
- if (irow >= (unsigned) m_frameContext->height()) {
- ipass++;
- irow = 0;
- }
- break;
- default:
- break;
- }
- } while (irow > (unsigned) (m_frameContext->height() - 1));
- }
- }
- // Perform Lempel-Ziv-Welch decoding.
- // Returns true if decoding was successful. In this case the block will have been completely consumed and/or rowsRemaining will be 0.
- // Otherwise, decoding failed; returns false in this case, which will always cause the SkGifImageReader to set the "decode failed" flag.
- bool SkGIFLZWContext::doLZW(const unsigned char* block, size_t bytesInBlock)
- {
- if (rowIter == rowBuffer.end())
- return true;
- const int width = m_frameContext->width();
- for (const unsigned char* ch = block; bytesInBlock-- > 0; ch++) {
- // Feed the next byte into the decoder's 32-bit input buffer.
- datum += ((int) *ch) << bits;
- bits += 8;
- // Check for underflow of decoder's 32-bit input buffer.
- while (bits >= codesize) {
- // Get the leading variable-length symbol from the data stream.
- int code = datum & codemask;
- datum >>= codesize;
- bits -= codesize;
- // Reset the dictionary to its original state, if requested.
- if (code == clearCode) {
- codesize = m_frameContext->dataSize() + 1;
- codemask = (1 << codesize) - 1;
- avail = clearCode + 2;
- oldcode = -1;
- continue;
- }
- // Check for explicit end-of-stream code.
- if (code == (clearCode + 1)) {
- // end-of-stream should only appear after all image data.
- if (!rowsRemaining)
- return true;
- return false;
- }
- const int tempCode = code;
- if (code > avail) {
- // This is an invalid code. The dictionary is just initialized
- // and the code is incomplete. We don't know how to handle
- // this case.
- return false;
- }
- if (code == avail) {
- if (oldcode != -1) {
- // This is a new code just being added to the dictionary.
- // It must encode the contents of the previous code, plus
- // the first character of the previous code again.
- // Now we know avail is the new code we can use oldcode
- // value to get the code related to that.
- code = oldcode;
- } else {
- // This is an invalid code. The dictionary is just initialized
- // and the code is incomplete. We don't know how to handle
- // this case.
- return false;
- }
- }
- // code length of the oldcode for new code which is
- // avail = oldcode + firstchar of the oldcode
- int remaining = suffixLength[code];
- // Round remaining up to multiple of SK_DICTIONARY_WORD_SIZE, because that's
- // the granularity of the chunks we copy. The last chunk may contain
- // some garbage but it'll be overwritten by the next code or left unused.
- // The working buffer is padded to account for this.
- remaining += -remaining & (SK_DICTIONARY_WORD_SIZE - 1) ;
- unsigned char* p = rowIter + remaining;
- // Place rowIter so that after writing pixels rowIter can be set to firstchar, thereby
- // completing the code.
- rowIter += suffixLength[code];
- while (remaining > 0) {
- p -= SK_DICTIONARY_WORD_SIZE;
- std::copy_n(suffix[code].begin(), SK_DICTIONARY_WORD_SIZE, p);
- code = prefix[code];
- remaining -= SK_DICTIONARY_WORD_SIZE;
- }
- const int firstchar = static_cast<unsigned char>(code); // (strictly `suffix[code][0]`)
- // This completes the new code avail and writing the corresponding
- // pixels on target.
- if (tempCode == avail) {
- *rowIter++ = firstchar;
- }
- // Define a new codeword in the dictionary as long as we've read
- // more than one value from the stream.
- if (avail < SK_MAX_DICTIONARY_ENTRIES && oldcode != -1) {
- // now add avail to the dictionary for future reference
- unsigned short codeLength = suffixLength[oldcode] + 1;
- int l = (codeLength - 1) & (SK_DICTIONARY_WORD_SIZE - 1);
- // If the suffix buffer is full (l == 0) then oldcode becomes the new
- // prefix, otherwise copy and extend oldcode's buffer and use the same
- // prefix as oldcode used.
- prefix[avail] = (l == 0) ? oldcode : prefix[oldcode];
- suffix[avail] = suffix[oldcode];
- suffix[avail][l] = firstchar;
- suffixLength[avail] = codeLength;
- ++avail;
- // If we've used up all the codewords of a given length
- // increase the length of codewords by one bit, but don't
- // exceed the specified maximum codeword size.
- if (!(avail & codemask) && avail < SK_MAX_DICTIONARY_ENTRIES) {
- ++codesize;
- codemask += avail;
- }
- }
- oldcode = tempCode;
- // Output as many rows as possible.
- unsigned char* rowBegin = rowBuffer.begin();
- for (; rowBegin + width <= rowIter; rowBegin += width) {
- outputRow(rowBegin);
- rowsRemaining--;
- if (!rowsRemaining)
- return true;
- }
- if (rowBegin != rowBuffer.begin()) {
- // Move the remaining bytes to the beginning of the buffer.
- const size_t bytesToCopy = rowIter - rowBegin;
- memcpy(&rowBuffer.front(), rowBegin, bytesToCopy);
- rowIter = rowBuffer.begin() + bytesToCopy;
- }
- }
- }
- return true;
- }
- sk_sp<SkColorTable> SkGIFColorMap::buildTable(SkStreamBuffer* streamBuffer, SkColorType colorType,
- int transparentPixel) const
- {
- if (!m_isDefined)
- return nullptr;
- const PackColorProc proc = choose_pack_color_proc(false, colorType);
- if (m_table && proc == m_packColorProc && m_transPixel == transparentPixel) {
- SkASSERT(transparentPixel == kNotFound || transparentPixel > m_table->count()
- || m_table->operator[](transparentPixel) == SK_ColorTRANSPARENT);
- // This SkColorTable has already been built with the same transparent color and
- // packing proc. Reuse it.
- return m_table;
- }
- m_packColorProc = proc;
- m_transPixel = transparentPixel;
- const size_t bytes = m_colors * SK_BYTES_PER_COLORMAP_ENTRY;
- sk_sp<SkData> rawData(streamBuffer->getDataAtPosition(m_position, bytes));
- if (!rawData) {
- return nullptr;
- }
- SkASSERT(m_colors <= SK_MAX_COLORS);
- const uint8_t* srcColormap = rawData->bytes();
- SkPMColor colorStorage[SK_MAX_COLORS];
- for (int i = 0; i < m_colors; i++) {
- if (i == transparentPixel) {
- colorStorage[i] = SK_ColorTRANSPARENT;
- } else {
- colorStorage[i] = proc(255, srcColormap[0], srcColormap[1], srcColormap[2]);
- }
- srcColormap += SK_BYTES_PER_COLORMAP_ENTRY;
- }
- for (int i = m_colors; i < SK_MAX_COLORS; i++) {
- colorStorage[i] = SK_ColorTRANSPARENT;
- }
- m_table = sk_sp<SkColorTable>(new SkColorTable(colorStorage, SK_MAX_COLORS));
- return m_table;
- }
- sk_sp<SkColorTable> SkGifImageReader::getColorTable(SkColorType colorType, int index) {
- if (index < 0 || index >= m_frames.count()) {
- return nullptr;
- }
- const SkGIFFrameContext* frameContext = m_frames[index].get();
- const SkGIFColorMap& localColorMap = frameContext->localColorMap();
- const int transPix = frameContext->transparentPixel();
- if (localColorMap.isDefined()) {
- return localColorMap.buildTable(&m_streamBuffer, colorType, transPix);
- }
- if (m_globalColorMap.isDefined()) {
- return m_globalColorMap.buildTable(&m_streamBuffer, colorType, transPix);
- }
- return nullptr;
- }
- // Perform decoding for this frame. frameComplete will be true if the entire frame is decoded.
- // Returns false if a decoding error occurred. This is a fatal error and causes the SkGifImageReader to set the "decode failed" flag.
- // Otherwise, either not enough data is available to decode further than before, or the new data has been decoded successfully; returns true in this case.
- bool SkGIFFrameContext::decode(SkStreamBuffer* streamBuffer, SkGifCodec* client,
- bool* frameComplete)
- {
- *frameComplete = false;
- if (!m_lzwContext) {
- // Wait for more data to properly initialize SkGIFLZWContext.
- if (!isDataSizeDefined() || !isHeaderDefined())
- return true;
- m_lzwContext.reset(new SkGIFLZWContext(client, this));
- if (!m_lzwContext->prepareToDecode()) {
- m_lzwContext.reset();
- return false;
- }
- m_currentLzwBlock = 0;
- }
- // Some bad GIFs have extra blocks beyond the last row, which we don't want to decode.
- while (m_currentLzwBlock < m_lzwBlocks.count() && m_lzwContext->hasRemainingRows()) {
- const auto& block = m_lzwBlocks[m_currentLzwBlock];
- const size_t len = block.blockSize;
- sk_sp<SkData> data(streamBuffer->getDataAtPosition(block.blockPosition, len));
- if (!data) {
- return false;
- }
- if (!m_lzwContext->doLZW(reinterpret_cast<const unsigned char*>(data->data()), len)) {
- return false;
- }
- ++m_currentLzwBlock;
- }
- // If this frame is data complete then the previous loop must have completely decoded all LZW blocks.
- // There will be no more decoding for this frame so it's time to cleanup.
- if (isComplete()) {
- *frameComplete = true;
- m_lzwContext.reset();
- }
- return true;
- }
- // Decode a frame.
- // This method uses SkGIFFrameContext:decode() to decode the frame; decoding error is reported to client as a critical failure.
- // Return true if decoding has progressed. Return false if an error has occurred.
- bool SkGifImageReader::decode(int frameIndex, bool* frameComplete)
- {
- SkGIFFrameContext* currentFrame = m_frames[frameIndex].get();
- return currentFrame->decode(&m_streamBuffer, m_client, frameComplete);
- }
- // Parse incoming GIF data stream into internal data structures.
- SkCodec::Result SkGifImageReader::parse(SkGifImageReader::SkGIFParseQuery query)
- {
- if (m_parseCompleted) {
- return SkCodec::kSuccess;
- }
- if (SkGIFLoopCountQuery == query && m_loopCount != cLoopCountNotSeen) {
- // Loop count has already been parsed.
- return SkCodec::kSuccess;
- }
- // SkGIFSizeQuery and SkGIFFrameCountQuery are negative, so this is only meaningful when >= 0.
- const int lastFrameToParse = (int) query;
- if (lastFrameToParse >= 0 && m_frames.count() > lastFrameToParse
- && m_frames[lastFrameToParse]->isComplete()) {
- // We have already parsed this frame.
- return SkCodec::kSuccess;
- }
- while (true) {
- if (!m_streamBuffer.buffer(m_bytesToConsume)) {
- // The stream does not yet have enough data.
- return SkCodec::kIncompleteInput;
- }
- switch (m_state) {
- case SkGIFLZW: {
- SkASSERT(!m_frames.empty());
- auto* frame = m_frames.back().get();
- frame->addLzwBlock(m_streamBuffer.markPosition(), m_bytesToConsume);
- GETN(1, SkGIFSubBlock);
- break;
- }
- case SkGIFLZWStart: {
- SkASSERT(!m_frames.empty());
- auto* currentFrame = m_frames.back().get();
- currentFrame->setDataSize(this->getOneByte());
- GETN(1, SkGIFSubBlock);
- break;
- }
- case SkGIFType: {
- const char* currentComponent = m_streamBuffer.get();
- // All GIF files begin with "GIF87a" or "GIF89a".
- if (!memcmp(currentComponent, "GIF89a", 6))
- m_version = 89;
- else if (!memcmp(currentComponent, "GIF87a", 6))
- m_version = 87;
- else {
- // This prevents attempting to continue reading this invalid stream.
- GETN(0, SkGIFDone);
- return SkCodec::kInvalidInput;
- }
- GETN(7, SkGIFGlobalHeader);
- break;
- }
- case SkGIFGlobalHeader: {
- const unsigned char* currentComponent =
- reinterpret_cast<const unsigned char*>(m_streamBuffer.get());
- // This is the height and width of the "screen" or frame into which
- // images are rendered. The individual images can be smaller than
- // the screen size and located with an origin anywhere within the
- // screen.
- // Note that we don't inform the client of the size yet, as it might
- // change after we read the first frame's image header.
- fScreenWidth = GETINT16(currentComponent);
- fScreenHeight = GETINT16(currentComponent + 2);
- const int globalColorMapColors = 2 << (currentComponent[4] & 0x07);
- if ((currentComponent[4] & 0x80) && globalColorMapColors > 0) { /* global map */
- m_globalColorMap.setNumColors(globalColorMapColors);
- GETN(SK_BYTES_PER_COLORMAP_ENTRY * globalColorMapColors, SkGIFGlobalColormap);
- break;
- }
- GETN(1, SkGIFImageStart);
- break;
- }
- case SkGIFGlobalColormap: {
- m_globalColorMap.setTablePosition(m_streamBuffer.markPosition());
- GETN(1, SkGIFImageStart);
- break;
- }
- case SkGIFImageStart: {
- const char currentComponent = m_streamBuffer.get()[0];
- if (currentComponent == '!') { // extension.
- GETN(2, SkGIFExtension);
- break;
- }
- if (currentComponent == ',') { // image separator.
- GETN(9, SkGIFImageHeader);
- break;
- }
- // If we get anything other than ',' (image separator), '!'
- // (extension), or ';' (trailer), there is extraneous data
- // between blocks. The GIF87a spec tells us to keep reading
- // until we find an image separator, but GIF89a says such
- // a file is corrupt. We follow Mozilla's implementation and
- // proceed as if the file were correctly terminated, so the
- // GIF will display.
- GETN(0, SkGIFDone);
- break;
- }
- case SkGIFExtension: {
- const unsigned char* currentComponent =
- reinterpret_cast<const unsigned char*>(m_streamBuffer.get());
- size_t bytesInBlock = currentComponent[1];
- SkGIFState exceptionState = SkGIFSkipBlock;
- switch (*currentComponent) {
- case 0xf9:
- // The GIF spec mandates that the GIFControlExtension header block length is 4 bytes,
- exceptionState = SkGIFControlExtension;
- // and the parser for this block reads 4 bytes, so we must enforce that the buffer
- // contains at least this many bytes. If the GIF specifies a different length, we
- // allow that, so long as it's larger; the additional data will simply be ignored.
- bytesInBlock = std::max(bytesInBlock, static_cast<size_t>(4));
- break;
- // The GIF spec also specifies the lengths of the following two extensions' headers
- // (as 12 and 11 bytes, respectively). Because we ignore the plain text extension entirely
- // and sanity-check the actual length of the application extension header before reading it,
- // we allow GIFs to deviate from these values in either direction. This is important for
- // real-world compatibility, as GIFs in the wild exist with application extension headers
- // that are both shorter and longer than 11 bytes.
- case 0x01:
- // ignoring plain text extension
- break;
- case 0xff:
- exceptionState = SkGIFApplicationExtension;
- break;
- case 0xfe:
- exceptionState = SkGIFConsumeComment;
- break;
- }
- if (bytesInBlock)
- GETN(bytesInBlock, exceptionState);
- else
- GETN(1, SkGIFImageStart);
- break;
- }
- case SkGIFConsumeBlock: {
- const unsigned char currentComponent = this->getOneByte();
- if (!currentComponent)
- GETN(1, SkGIFImageStart);
- else
- GETN(currentComponent, SkGIFSkipBlock);
- break;
- }
- case SkGIFSkipBlock: {
- GETN(1, SkGIFConsumeBlock);
- break;
- }
- case SkGIFControlExtension: {
- const unsigned char* currentComponent =
- reinterpret_cast<const unsigned char*>(m_streamBuffer.get());
- addFrameIfNecessary();
- SkGIFFrameContext* currentFrame = m_frames.back().get();
- if (*currentComponent & 0x1)
- currentFrame->setTransparentPixel(currentComponent[3]);
- // We ignore the "user input" bit.
- // NOTE: This relies on the values in the FrameDisposalMethod enum
- // matching those in the GIF spec!
- int rawDisposalMethod = ((*currentComponent) >> 2) & 0x7;
- switch (rawDisposalMethod) {
- case 1:
- case 2:
- case 3:
- currentFrame->setDisposalMethod((SkCodecAnimation::DisposalMethod) rawDisposalMethod);
- break;
- case 4:
- // Some specs say that disposal method 3 is "overwrite previous", others that setting
- // the third bit of the field (i.e. method 4) is. We map both to the same value.
- currentFrame->setDisposalMethod(SkCodecAnimation::DisposalMethod::kRestorePrevious);
- break;
- default:
- // Other values use the default.
- currentFrame->setDisposalMethod(SkCodecAnimation::DisposalMethod::kKeep);
- break;
- }
- currentFrame->setDuration(GETINT16(currentComponent + 1) * 10);
- GETN(1, SkGIFConsumeBlock);
- break;
- }
- case SkGIFCommentExtension: {
- const unsigned char currentComponent = this->getOneByte();
- if (currentComponent)
- GETN(currentComponent, SkGIFConsumeComment);
- else
- GETN(1, SkGIFImageStart);
- break;
- }
- case SkGIFConsumeComment: {
- GETN(1, SkGIFCommentExtension);
- break;
- }
- case SkGIFApplicationExtension: {
- // Check for netscape application extension.
- if (m_bytesToConsume == 11) {
- const unsigned char* currentComponent =
- reinterpret_cast<const unsigned char*>(m_streamBuffer.get());
- if (!memcmp(currentComponent, "NETSCAPE2.0", 11) || !memcmp(currentComponent, "ANIMEXTS1.0", 11))
- GETN(1, SkGIFNetscapeExtensionBlock);
- }
- if (m_state != SkGIFNetscapeExtensionBlock)
- GETN(1, SkGIFConsumeBlock);
- break;
- }
- // Netscape-specific GIF extension: animation looping.
- case SkGIFNetscapeExtensionBlock: {
- const int currentComponent = this->getOneByte();
- // SkGIFConsumeNetscapeExtension always reads 3 bytes from the stream; we should at least wait for this amount.
- if (currentComponent)
- GETN(std::max(3, currentComponent), SkGIFConsumeNetscapeExtension);
- else
- GETN(1, SkGIFImageStart);
- break;
- }
- // Parse netscape-specific application extensions
- case SkGIFConsumeNetscapeExtension: {
- const unsigned char* currentComponent =
- reinterpret_cast<const unsigned char*>(m_streamBuffer.get());
- int netscapeExtension = currentComponent[0] & 7;
- // Loop entire animation specified # of times. Only read the loop count during the first iteration.
- if (netscapeExtension == 1) {
- m_loopCount = GETINT16(currentComponent + 1);
- // Zero loop count is infinite animation loop request.
- if (!m_loopCount)
- m_loopCount = SkCodec::kRepetitionCountInfinite;
- GETN(1, SkGIFNetscapeExtensionBlock);
- if (SkGIFLoopCountQuery == query) {
- m_streamBuffer.flush();
- return SkCodec::kSuccess;
- }
- } else if (netscapeExtension == 2) {
- // Wait for specified # of bytes to enter buffer.
- // Don't do this, this extension doesn't exist (isn't used at all)
- // and doesn't do anything, as our streaming/buffering takes care of it all...
- // See: http://semmix.pl/color/exgraf/eeg24.htm
- GETN(1, SkGIFNetscapeExtensionBlock);
- } else {
- // 0,3-7 are yet to be defined netscape extension codes
- // This prevents attempting to continue reading this invalid stream.
- GETN(0, SkGIFDone);
- return SkCodec::kInvalidInput;
- }
- break;
- }
- case SkGIFImageHeader: {
- int height, width, xOffset, yOffset;
- const unsigned char* currentComponent =
- reinterpret_cast<const unsigned char*>(m_streamBuffer.get());
- /* Get image offsets, with respect to the screen origin */
- xOffset = GETINT16(currentComponent);
- yOffset = GETINT16(currentComponent + 2);
- /* Get image width and height. */
- width = GETINT16(currentComponent + 4);
- height = GETINT16(currentComponent + 6);
- // Some GIF files have frames that don't fit in the specified
- // overall image size. For the first frame, we can simply enlarge
- // the image size to allow the frame to be visible. We can't do
- // this on subsequent frames because the rest of the decoding
- // infrastructure assumes the image size won't change as we
- // continue decoding, so any subsequent frames that are even
- // larger will be cropped.
- // Luckily, handling just the first frame is sufficient to deal
- // with most cases, e.g. ones where the image size is erroneously
- // set to zero, since usually the first frame completely fills
- // the image.
- if (currentFrameIsFirstFrame()) {
- fScreenHeight = std::max(fScreenHeight, yOffset + height);
- fScreenWidth = std::max(fScreenWidth, xOffset + width);
- }
- // NOTE: Chromium placed this block after setHeaderDefined, down
- // below we returned true when asked for the size. So Chromium
- // created an image which would fail. Is this the correct behavior?
- // We choose to return false early, so we will not create an
- // SkCodec.
- // Work around more broken GIF files that have zero image width or
- // height.
- if (!height || !width) {
- height = fScreenHeight;
- width = fScreenWidth;
- if (!height || !width) {
- // This prevents attempting to continue reading this invalid stream.
- GETN(0, SkGIFDone);
- return SkCodec::kInvalidInput;
- }
- }
- const bool isLocalColormapDefined = SkToBool(currentComponent[8] & 0x80);
- // The three low-order bits of currentComponent[8] specify the bits per pixel.
- const int numColors = 2 << (currentComponent[8] & 0x7);
- if (currentFrameIsFirstFrame()) {
- const int transPix = m_frames.empty() ? SkGIFColorMap::kNotFound
- : m_frames[0]->transparentPixel();
- if (is_palette_index_valid(transPix)) {
- m_firstFrameHasAlpha = true;
- } else {
- const bool frameIsSubset = xOffset > 0 || yOffset > 0
- || width < fScreenWidth
- || height < fScreenHeight;
- m_firstFrameHasAlpha = frameIsSubset;
- }
- }
- addFrameIfNecessary();
- SkGIFFrameContext* currentFrame = m_frames.back().get();
- currentFrame->setHeaderDefined();
- if (query == SkGIFSizeQuery) {
- // The decoder needs to stop, so we return here, before
- // flushing the buffer. Next time through, we'll be in the same
- // state, requiring the same amount in the buffer.
- return SkCodec::kSuccess;
- }
- currentFrame->setXYWH(xOffset, yOffset, width, height);
- currentFrame->setInterlaced(SkToBool(currentComponent[8] & 0x40));
- // Overlaying interlaced, transparent GIFs over
- // existing image data using the Haeberli display hack
- // requires saving the underlying image in order to
- // avoid jaggies at the transparency edges. We are
- // unprepared to deal with that, so don't display such
- // images progressively. Which means only the first
- // frame can be progressively displayed.
- // FIXME: It is possible that a non-transparent frame
- // can be interlaced and progressively displayed.
- currentFrame->setProgressiveDisplay(currentFrameIsFirstFrame());
- if (isLocalColormapDefined) {
- currentFrame->localColorMap().setNumColors(numColors);
- GETN(SK_BYTES_PER_COLORMAP_ENTRY * numColors, SkGIFImageColormap);
- break;
- }
- setAlphaAndRequiredFrame(currentFrame);
- GETN(1, SkGIFLZWStart);
- break;
- }
- case SkGIFImageColormap: {
- SkASSERT(!m_frames.empty());
- auto* currentFrame = m_frames.back().get();
- auto& cmap = currentFrame->localColorMap();
- cmap.setTablePosition(m_streamBuffer.markPosition());
- setAlphaAndRequiredFrame(currentFrame);
- GETN(1, SkGIFLZWStart);
- break;
- }
- case SkGIFSubBlock: {
- const size_t bytesInBlock = this->getOneByte();
- if (bytesInBlock)
- GETN(bytesInBlock, SkGIFLZW);
- else {
- // Finished parsing one frame; Process next frame.
- SkASSERT(!m_frames.empty());
- // Note that some broken GIF files do not have enough LZW blocks to fully
- // decode all rows but we treat it as frame complete.
- m_frames.back()->setComplete();
- GETN(1, SkGIFImageStart);
- if (lastFrameToParse >= 0 && m_frames.count() > lastFrameToParse) {
- m_streamBuffer.flush();
- return SkCodec::kSuccess;
- }
- }
- break;
- }
- case SkGIFDone: {
- m_parseCompleted = true;
- return SkCodec::kSuccess;
- }
- default:
- // We shouldn't ever get here.
- // This prevents attempting to continue reading this invalid stream.
- GETN(0, SkGIFDone);
- return SkCodec::kInvalidInput;
- break;
- } // switch
- m_streamBuffer.flush();
- }
- }
- void SkGifImageReader::addFrameIfNecessary()
- {
- if (m_frames.empty() || m_frames.back()->isComplete()) {
- const int i = m_frames.count();
- m_frames.emplace_back(new SkGIFFrameContext(i));
- }
- }
- SkEncodedInfo::Alpha SkGIFFrameContext::onReportedAlpha() const {
- // Note: We could correct these after decoding - i.e. some frames may turn out to be
- // independent and opaque if they do not use the transparent pixel, but that would require
- // checking whether each pixel used the transparent index.
- return is_palette_index_valid(this->transparentPixel()) ? SkEncodedInfo::kBinary_Alpha
- : SkEncodedInfo::kOpaque_Alpha;
- }
- // FIXME: Move this method to close to doLZW().
- bool SkGIFLZWContext::prepareToDecode()
- {
- SkASSERT(m_frameContext->isDataSizeDefined() && m_frameContext->isHeaderDefined());
- // Since we use a codesize of 1 more than the datasize, we need to ensure
- // that our datasize is strictly less than the SK_MAX_DICTIONARY_ENTRY_BITS.
- if (m_frameContext->dataSize() >= SK_MAX_DICTIONARY_ENTRY_BITS)
- return false;
- clearCode = 1 << m_frameContext->dataSize();
- avail = clearCode + 2;
- oldcode = -1;
- codesize = m_frameContext->dataSize() + 1;
- codemask = (1 << codesize) - 1;
- datum = bits = 0;
- ipass = m_frameContext->interlaced() ? 1 : 0;
- irow = 0;
- // We want to know the longest sequence encodable by a dictionary with
- // SK_MAX_DICTIONARY_ENTRIES entries. If we ignore the need to encode the base
- // values themselves at the beginning of the dictionary, as well as the need
- // for a clear code or a termination code, we could use every entry to
- // encode a series of multiple values. If the input value stream looked
- // like "AAAAA..." (a long string of just one value), the first dictionary
- // entry would encode AA, the next AAA, the next AAAA, and so forth. Thus
- // the longest sequence would be SK_MAX_DICTIONARY_ENTRIES + 1 values.
- //
- // However, we have to account for reserved entries. The first |datasize|
- // bits are reserved for the base values, and the next two entries are
- // reserved for the clear code and termination code. In theory a GIF can
- // set the datasize to 0, meaning we have just two reserved entries, making
- // the longest sequence (SK_MAX_DICTIONARY_ENTIRES + 1) - 2 values long. Since
- // each value is a byte, this is also the number of bytes in the longest
- // encodable sequence.
- constexpr size_t kMaxSequence = SK_MAX_DICTIONARY_ENTRIES - 1;
- constexpr size_t kMaxBytes = (kMaxSequence + SK_DICTIONARY_WORD_SIZE - 1)
- & ~(SK_DICTIONARY_WORD_SIZE - 1);
- // Now allocate the output buffer. We decode directly into this buffer
- // until we have at least one row worth of data, then call outputRow().
- // This means worst case we may have (row width - 1) bytes in the buffer
- // and then decode a sequence |kMaxBytes| long to append.
- rowBuffer.reset(m_frameContext->width() - 1 + kMaxBytes);
- rowIter = rowBuffer.begin();
- rowsRemaining = m_frameContext->height();
- // Clearing the whole suffix table lets us be more tolerant of bad data.
- for (int i = 0; i < clearCode; ++i) {
- std::fill_n(suffix[i].begin(), SK_DICTIONARY_WORD_SIZE, 0);
- suffix[i][0] = i;
- suffixLength[i] = 1;
- prefix[i] = i; // ensure that we have a place to find firstchar
- }
- return true;
- }
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