public static void UpdateGifAnimationContext(WicGifContainer cont, ComPtr <IWICBitmapSource> src, ComPtr <IWICMetadataQueryReader> meta)
{
Debug.Assert(cont.AnimationContext is not null);
var anictx = cont.AnimationContext;
const int bytesPerPixel = 4;
var finfo = GetGifFrameInfo(cont, src, meta);
var fbuff = anictx.FrameBufferSource ??= new FrameBufferSource(cont.ScreenWidth, cont.ScreenHeight, PixelFormat.Bgra32Bpp);
var bspan = fbuff.Span;
fbuff.ResumeTiming();
// Most GIF viewers clear the background to transparent instead of the background color when the next frame has transparency
bool ftrans = meta.GetValueOrDefault <bool>(Wic.Metadata.Gif.TransparencyFlag);
if (!finfo.FullScreen && anictx.LastDisposal == GifDisposalMethod.RestoreBackground)
{
MemoryMarshal.Cast <byte, uint>(bspan).Fill(ftrans ? 0 : cont.BackgroundColor);
}
// Similarly, they overwrite a background color with transparent pixels but overlay instead when the previous frame is preserved
var fspan = bspan.Slice(finfo.Top * fbuff.Stride + finfo.Left * bytesPerPixel);
fixed(byte *buff = fspan)
{
if (!ftrans || anictx.LastDisposal == GifDisposalMethod.RestoreBackground)
{
var rect = new WICRect {
Width = finfo.Width, Height = finfo.Height
};
HRESULT.Check(src.Get()->CopyPixels(&rect, (uint)fbuff.Stride, (uint)fspan.Length, buff));
}
else
{
using var overlay = new OverlayTransform(fbuff, src.AsPixelSource(null, nameof(IWICBitmapFrameDecode), false), finfo.Left, finfo.Top, true, true);
overlay.CopyPixels(new PixelArea(finfo.Left, finfo.Top, finfo.Width, finfo.Height), fbuff.Stride, fspan.Length, (IntPtr)buff);
}
}
fbuff.PauseTiming();
}