Implement IReadableBitmapImpl in SurfaceRenderTarget

[llfab]

Avalonia.Skia.SurfaceRenderTarget would have enough information to allow reading the bitmap content. Hence it would be possible to implement IReadableBitmapImpl like this:

        /// <summary>
        /// Returns the null because we do not own a format
        /// </summary>
        PixelFormat? IReadableBitmapImpl.Format => null;

        /// <summary>
        /// Creates a copy of the <see cref="SKSurface.Snapshot()"/> and provides it via
        /// a <see cref="LockedFramebuffer"/>
        /// </summary>
        /// <returns>A copy of the image data</returns>
        ILockedFramebuffer IReadableBitmapImpl.Lock()
        {
            if (_surface.Surface == null)
                throw new NotSupportedException();

            using (SKImage image = SnapshotImage())
            {
                SKBitmap bitmap = SKBitmap.FromImage(image);
                return new LockedFramebuffer(bitmap.GetPixels(), PixelSize, bitmap.RowBytes, Dpi,
                    image.ColorType.ToAvalonia().Value, () => bitmap.Dispose());
            }
        }

That would allow to call RenderTargetBitmap.CopyPixels() to be used.

Opinions?

[kekekeks]

Are you trying to use it from the UI thread?

[llfab]

Currently I am using it from the UI thread but that is not important for me, Basically I want to get the Control into a pixel image.

[kekekeks]

Ah, so it's for RenderTargetBitmap?

[llfab]

Yes

[llfab]

I have created a draft PR so I can test if it even works correctly: #10284

[llfab]

What about this change to RenderTargetBitmap:

        /// <summary>
        /// Overrides the <see cref="Bitmap"/> implementation 
        /// skipping the <see cref="Format"/> null check
        /// </summary>
        public override void CopyPixels(PixelRect sourceRect, nint buffer, int bufferSize, int stride)
        {
            // only check if we have a readable bitmap and if the formats are identical
            // this also allows for both formats being null
            if (PlatformImpl.Item is not IReadableBitmapImpl readable
                || Format != readable.Format
            )
                throw new NotSupportedException("CopyPixels is not supported for this bitmap type");

            using (var fb = readable.Lock())
                CopyPixelsCore(sourceRect, buffer, bufferSize, stride, fb);
        }