void WriteFrame(Frame frame)
{
Trace.WriteLine(string.Format("Gif89a.WriteFrame [{0}]", System.Threading.Thread.CurrentThread.ManagedThreadId));
var sw = new Stopwatch();
sw.Start();
if (frame.OpaqueFramePixelBytes == null)
{
return;
}
// if we're discarding duplicate frames
if (frame.OpaqueFramePixelBytes.Length == 0 && this.optimization.HasFlag(FrameOptimization.DiscardDuplicates))
{
// hang on to where we currently are in the output stream
var here = this.output.Position;
// the last written GCE might be more than one frame back, if there's a bunch of duplicates
var prev = frame;
while (prev.OutputStreamGCEIndex == 0)
{
prev = this.frames[this.frames.IndexOf(prev) - 1];
}
// jump back to the GCE in the previous frame
this.output.Position = prev.OutputStreamGCEIndex;
prev.Delay += frame.Delay;
GifFileFormat.WriteGraphicControlExtension(output, prev, prev.transIndex);
// jump forward to where we just were to continue on normally
this.output.Position = here;
return;
}
if (frame.IndexedPixels.Length == 0)
{
return;
}
if (frame == this.frames.First())
{
// logical screen descriptor
GifFileFormat.WriteLogicalScreenDescriptor(this.output, (ushort)this.Size.Width, (ushort)this.Size.Height, frame.ColorTableBytes.Length);
// global color table
GifFileFormat.WriteColorTable(this.output, frame.ColorTableBytes);
if (this.Repeat >= 0)
{
// use NS app extension to indicate reps
GifFileFormat.WriteNetscapeApplicationExtension(this.output, this.Repeat);
}
}
// write graphic control extension
frame.OutputStreamGCEIndex = this.output.Position;
GifFileFormat.WriteGraphicControlExtension(output, frame, frame.transIndex);
// image descriptor
GifFileFormat.WriteImageDescriptor(this.output, frame.ChangeRect, frame.ColorTableBytes.Length, frame == this.frames.First());
if (frame != this.frames.First())
{
// local color table
GifFileFormat.WriteColorTable(this.output, frame.ColorTableBytes);
}
// encode and write pixel data
var lzw = new LZWEncoder(frame.ChangeRect.Width, frame.ChangeRect.Height, frame.IndexedPixels, 8);
lzw.encode(this.output);
sw.Stop();
Trace.WriteLine($"Done ({ sw.Elapsed })", string.Format("Gif89a.WriteFrame [{0}]", System.Threading.Thread.CurrentThread.ManagedThreadId));
}
void WriteGifToStream()
{
Trace.WriteLine(string.Format("Gif89a.WriteGifToStream [{0}]", System.Threading.Thread.CurrentThread.ManagedThreadId));
GifFileFormat.WriteFileHeader(this.output);
var nextFrameIndex = 0;
var pendingFrames = new List <Frame>();
while (!FrameWriteQueue.IsCompleted)
{
Frame someFrame = null;
try
{
someFrame = FrameWriteQueue.Take();
}
catch (InvalidOperationException)
{
Trace.WriteLine("No more frames to write", string.Format("Gif89a.WriteGifToStream [{0}]", System.Threading.Thread.CurrentThread.ManagedThreadId));
break;
}
// frame analysis could can (and does!) occur out-of-order
// so every time a frame is popped from the FrameWriteQueue, it might not be the "next" frame
// no problem: just hang on to the writable frames and then write as much as possible in order
pendingFrames.Add(someFrame);
while (nextFrameIndex < this.frames.Count && pendingFrames.Contains(this.frames[nextFrameIndex]))
{
this.WriteFrame(this.frames[nextFrameIndex]);
// no need to hang on to it here any more
pendingFrames.Remove(someFrame);
// we're done with the raw frame data, so let it unload
if (nextFrameIndex > 0)
{
// don't dispose the current frame, since it could be a "prev" frame for a frame that's currently being analyzed
this.frames[nextFrameIndex - 1].Dispose();
}
// allow more frames to be loaded
FrameLoadingDelay.Set();
this.OnFrameWriteProgress?.Invoke(this, new FrameWriteProgressEventArgs((float)nextFrameIndex * 100.0f / (float)(this.frames.Count + this.FrameLoadingQueue.Count)));
nextFrameIndex++;
}
output.Flush();
}
// the final frame is now safe to dispose since there's no "next" for it to be a "prev" for
if (this.frames.Any())
{
this.frames.Last().Dispose();
}
GifFileFormat.WriteFileTrailer(output);
output.Flush();
Trace.WriteLine("Done", string.Format("Gif89a.WriteGifToStream [{0}]", System.Threading.Thread.CurrentThread.ManagedThreadId));
// announce that stream writing is done
FrameWriteComplete.Set();
}
