internal new static async Task<GifFrame> ReadAsync(Stream stream, IEnumerable<GifExtension> controlExtensions)
{
var frame = new GifFrame();
await frame.ReadInternalAsync(stream, controlExtensions).ConfigureAwait(false);
return frame;
}
private static TimeSpan GetFrameDelay(GifFrame frame)
{
var gce = frame.GraphicControl;
if (gce != null)
{
if (gce.Delay != 0)
return TimeSpan.FromMilliseconds(gce.Delay);
}
return TimeSpan.FromMilliseconds(100);
}
private async Task<Stream> GetIndexStreamAsync(GifFrame frame, CancellationToken cancellationToken)
{
var data = frame.ImageData;
cancellationToken.ThrowIfCancellationRequested();
_sourceStream.Seek(data.CompressedDataStartOffset, SeekOrigin.Begin);
using (var ms = new MemoryStream(_indexStreamBuffer))
{
await GifHelpers.CopyDataBlocksToStreamAsync(_sourceStream, ms, cancellationToken).ConfigureAwait(false);
}
var lzwStream = new LzwDecompressStream(_indexStreamBuffer, data.LzwMinimumCodeSize);
return lzwStream;
}
private void DisposePreviousFrame(GifFrame currentFrame)
{
var pgce = _previousFrame?.GraphicControl;
if (pgce != null)
{
switch (pgce.DisposalMethod)
{
case GifFrameDisposalMethod.None:
case GifFrameDisposalMethod.DoNotDispose:
{
// Leave previous frame in place
break;
}
case GifFrameDisposalMethod.RestoreBackground:
{
ClearArea(_previousFrame.Descriptor);
break;
}
case GifFrameDisposalMethod.RestorePrevious:
{
CopyToBitmap(_previousBackBuffer, _bitmap, 0, _previousBackBuffer.Length);
#if WPF
var desc = _metadata.Header.LogicalScreenDescriptor;
var rect = new Int32Rect(0, 0, desc.Width, desc.Height);
_bitmap.AddDirtyRect(rect);
#endif
break;
}
default:
{
throw new ArgumentOutOfRangeException();
}
}
}
var gce = currentFrame.GraphicControl;
if (gce != null && gce.DisposalMethod == GifFrameDisposalMethod.RestorePrevious)
{
CopyFromBitmap(_previousBackBuffer, _bitmap, 0, _previousBackBuffer.Length);
}
}
private async Task RenderFrameAsync(int frameIndex, CancellationToken cancellationToken)
{
if (frameIndex < 0)
return;
var frame = _metadata.Frames[frameIndex];
var desc = frame.Descriptor;
using (var indexStream = await GetIndexStreamAsync(frame, cancellationToken))
{
#if WPF
_bitmap.Lock();
try
{
#endif
if (frameIndex < _previousFrameIndex)
ClearArea(_metadata.Header.LogicalScreenDescriptor);
else
DisposePreviousFrame(frame);
int bufferLength = 4 * desc.Width;
byte[] indexBuffer = new byte[desc.Width];
byte[] lineBuffer = new byte[bufferLength];
var palette = _palettes[frameIndex];
int transparencyIndex = palette.TransparencyIndex ?? -1;
var rows = frame.Descriptor.Interlace
? InterlacedRows(frame.Descriptor.Height)
: NormalRows(frame.Descriptor.Height);
foreach (int y in rows)
{
int read = indexStream.Read(indexBuffer, 0, desc.Width);
if (read != desc.Width)
throw new EndOfStreamException();
int offset = (desc.Top + y) * _stride + desc.Left * 4;
if (transparencyIndex >= 0)
{
CopyFromBitmap(lineBuffer, _bitmap, offset, bufferLength);
}
for (int x = 0; x < desc.Width; x++)
{
byte index = indexBuffer[x];
int i = 4 * x;
if (index != transparencyIndex)
{
WriteColor(lineBuffer, palette[index], i);
}
}
CopyToBitmap(lineBuffer, _bitmap, offset, bufferLength);
}
#if WPF
var rect = new Int32Rect(desc.Left, desc.Top, desc.Width, desc.Height);
_bitmap.AddDirtyRect(rect);
}
finally
{
_bitmap.Unlock();
}
#elif WINRT
_bitmap.Invalidate();
#endif
_previousFrame = frame;
_previousFrameIndex = frameIndex;
}
}
