GIF exporter: previous frames do not dispose on gifs with trnasparency

[gritsenko]

Hi! I'm trying to save animated gif composed from few bitmaps with transparency and it doesn't remove previous frame from animation. How can it be fixed?

Here is the result file:

My code:
`
var outputFrames = new List();
for (inti = 0; i <= animationLength; i++)
{
CanvasRenderTarget offscreen = await Export(settings, vp, i);

                IBuffer buff = offscreen.GetPixelBytes().AsBuffer();

                SoftwareBitmap bm = SoftwareBitmap.CreateCopyFromBuffer(buff, BitmapPixelFormat.Bgra8, (int)offscreen.SizeInPixels.Width, (int)offscreen.SizeInPixels.Height);
                SoftwareBitmapImageSource bs = new SoftwareBitmapImageSource(bm);

                outputFrames.Add(bs);
            }

            using (var gifRenderer = new GifRenderer())
            {
                gifRenderer.Duration = 100;
                gifRenderer.NumberOfAnimationLoops = 10000;
                gifRenderer.UseGlobalPalette = false;
                gifRenderer.ApplyDithering = false;
                gifRenderer.Sources = outputFrames.ToArray();


                var buffer = await gifRenderer.RenderAsync();
                using (var stream = await fileToSave.OpenAsync(FileAccessMode.ReadWrite))
                {
                    await stream.WriteAsync(buffer);
                }
            }

`

[davidbozjak]

Hi,

Is it possible that you are using transparency in your frames? This is the result I would expect in case when you are only setting the pixels where your content (circle/ellipse in your case) appears, and leaving everything else unset - transparent.

You can either make sure that the API you are exporting the frames from has a background color, or you can blend in the background color with Lumia Imaging SDK before rendering.

[gritsenko]

Hi David! Yes I use transparency. When I don't everything is fine.
But I need to save animation With transparency. So I asked if there is any way to dispose previous frames?

[davidbozjak]

No, not easily, that I'm aware off. I will investigate a bit and get back to you, but I think you will need to paint over the area in the previous frame with a background color, and then paint over your next frame.

I realize this is not ideal for your scenario...

[gritsenko]

In photoshop and Gimp there are option "dispose frame"
like here:
https://s3.amazonaws.com/satisfaction-production/s3_images/683741/disposal_inline.

and it allowed me to make:

may be there is a way to erase area from previous frame with transparent color?