Decode GIF image frames on demand.

Source/core/platform/image-decoders/gif/GIFImageReader.cpp

 /* -*- Mode: C; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
  *
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  * the License. You may obtain a copy of the License at
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  * Software distributed under the License is distributed on an "AS IS" basis,
@@ skipping 333 matching lines @@
 
     // 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()) {
         *frameDecoded = true;
         m_lzwContext.clear();
     }
     return true;
 }
 
-// Decode all frames before haltAtFrame.
+// Decode frames. The frames must have been parsed.
 // This method uses GIFFrameContext:decode() to decode each 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 GIFImageReader::decode(GIFImageDecoder::GIFQuery query, unsigned haltAtFrame)
+bool GIFImageReader::decode(const BitVector& frames)
 {
-    ASSERT(m_bytesRead <= m_data->size());
+    for (size_t i = 0; i < frames.size(); ++i) {

[Alpha Left Google, 2013/05/18 00:39:35]

I would rather let the user of this API to call multiple times for each frame it
wants to decode.

[Xianzhu, 2013/05/20 04:30:59]

Done.

+        if (!frames.get(i))
+            continue;
 
-    if (!parse(m_bytesRead, m_data->size() - m_bytesRead, query == GIFImageDecoder::GIFSizeQuery))
-        return false;
-
-    if (query != GIFImageDecoder::GIFFullQuery)
-        return true;
-
-    while (m_currentDecodingFrame < std::min(m_frames.size(), static_cast<size_t>(haltAtFrame))) {
         bool frameDecoded = false;
-        GIFFrameContext* currentFrame = m_frames[m_currentDecodingFrame].get();
+        GIFFrameContext* currentFrame = m_frames[i].get();
 
         if (!currentFrame->decode(data(0), m_data->size(), m_client, &frameDecoded))
             return false;
 
         // We need more data to continue decoding.
         if (!frameDecoded)
             break;
 
-        if (!m_client->frameComplete(m_currentDecodingFrame, currentFrame->delayTime, currentFrame->disposalMethod))
+        if (!m_client->frameComplete(i, currentFrame->delayTime, currentFrame->disposalMethod))
             return false;
-        ++m_currentDecodingFrame;
+
+        m_decodedFramesCount++;

[Alpha Left Google, 2013/05/18 00:39:35]

See my comments below, I don't think we need to do this any more.

[Xianzhu, 2013/05/20 04:30:59]

Done.

     }
 
     // All frames decoded.
-    if (m_currentDecodingFrame == m_frames.size() && m_parseCompleted)
+    if (m_decodedFramesCount == m_frames.size() && m_parseCompleted)

[Alpha Left Google, 2013/05/18 00:39:35]

This check will not be correct because we now allow the GIF image to be decoded
at random index, so a frame can be decoded more than once.

My intention was to remove the call to m_client->gifComplete() because it
doesn't apply any more if we're not decoding serially.

[Xianzhu, 2013/05/20 04:30:59]

Done.

         m_client->gifComplete();
     return true;
 }
 
+bool GIFImageReader::parse(GIFImageDecoder::GIFParseQuery query)
+{
+    ASSERT(m_bytesRead <= m_data->size());
+
+    return parseData(m_bytesRead, m_data->size() - m_bytesRead, query);
+}
+
 // Parse incoming GIF data stream into internal data structures.
 // Return true if parsing has progressed or there is not enough data.
 // Return false if a fatal error is encountered.
-bool GIFImageReader::parse(size_t dataPosition, size_t len, bool parseSizeOnly)
+bool GIFImageReader::parseData(size_t dataPosition, size_t len, GIFImageDecoder::GIFParseQuery query)
 {
     if (!len) {
         // No new data has come in since the last call, just ignore this call.
         return true;
     }
 
     if (len < m_bytesToConsume)
         return true;
 
     // This loop reads as many components from |m_data| as possible.
@@ skipping 266 matching lines @@
             }
 
             // Work around more broken GIF files that have zero image width or height
             if (!height || !width) {
                 height = m_screenHeight;
                 width = m_screenWidth;
                 if (!height || !width)
                     return false;
             }
 
-            if (parseSizeOnly) {
+            if (query == GIFImageDecoder::GIFSizeQuery) {
                 // The decoder needs to stop. Hand back the number of bytes we consumed from
                 // buffer minus 9 (the amount we consumed to read the header).
                 setRemainingBytes(len + 9);
                 GETN(9, GIFImageHeader);
                 return true;
             }
 
             addFrameIfNecessary();
             GIFFrameContext* currentFrame = m_frames.last().get();
 
@@ skipping 126 matching lines @@
     rowPosition = 0;
     rowsRemaining = m_frameContext->height;
 
     // Clearing the whole suffix table lets us be more tolerant of bad data.
     suffix.fill(0);
     for (int i = 0; i < clearCode; i++)
         suffix[i] = i;
     stackp = 0;
     return true;
 }