Don't use manual FBO for RenderTargetBitmap/VisualBrush.

Fixes the first part of #4944.

src/Skia/Avalonia.Skia/DrawingContextImpl.cs

@@ -434,7 +434,7 @@ namespace Avalonia.Skia
         /// <inheritdoc />
         public IDrawingContextLayerImpl CreateLayer(Size size)
         {
-            return CreateRenderTarget( size);
+            return CreateRenderTarget(size, true);
         }
 
         /// <inheritdoc />
@@ -673,7 +673,7 @@ namespace Avalonia.Skia
         private void ConfigureTileBrush(ref PaintWrapper paintWrapper, Size targetSize, ITileBrush tileBrush, IDrawableBitmapImpl tileBrushImage)
         {
             var calc = new TileBrushCalculator(tileBrush, tileBrushImage.PixelSize.ToSizeWithDpi(_dpi), targetSize);
-            var intermediate = CreateRenderTarget(calc.IntermediateSize);
+            var intermediate = CreateRenderTarget(calc.IntermediateSize, false);
 
             paintWrapper.AddDisposable(intermediate);
 
@@ -748,7 +748,7 @@ namespace Avalonia.Skia
 
             if (intermediateSize.Width >= 1 && intermediateSize.Height >= 1)
             {
-                var intermediate = CreateRenderTarget(intermediateSize);
+                var intermediate = CreateRenderTarget(intermediateSize, false);
 
                 using (var ctx = intermediate.CreateDrawingContext(visualBrushRenderer))
                 {
@@ -978,9 +978,10 @@ namespace Avalonia.Skia
         /// Create new render target compatible with this drawing context.
         /// </summary>
         /// <param name="size">The size of the render target in DIPs.</param>
+        /// <param name="isLayer">Whether the render target is being created for a layer.</param>
         /// <param name="format">Pixel format.</param>
         /// <returns></returns>
-        private SurfaceRenderTarget CreateRenderTarget(Size size, PixelFormat? format = null)
+        private SurfaceRenderTarget CreateRenderTarget(Size size, bool isLayer, PixelFormat? format = null)
         {
             var pixelSize = PixelSize.FromSizeWithDpi(size, _dpi);
             var createInfo = new SurfaceRenderTarget.CreateInfo
@@ -992,7 +993,8 @@ namespace Avalonia.Skia
                 DisableTextLcdRendering = !_canTextUseLcdRendering,
                 GrContext = _grContext,
                 Gpu = _gpu,
-                Session = _session
+                Session = _session,
+                DisableManualFbo = !isLayer,
             };
 
             return new SurfaceRenderTarget(createInfo);

src/Skia/Avalonia.Skia/PlatformRenderInterface.cs

@@ -124,7 +124,8 @@ namespace Avalonia.Skia
                 Width = size.Width,
                 Height = size.Height,
                 Dpi = dpi,
-                DisableTextLcdRendering = false
+                DisableTextLcdRendering = false,
+                DisableManualFbo = true,
             };
 
             return new SurfaceRenderTarget(createInfo);

src/Skia/Avalonia.Skia/SurfaceRenderTarget.cs

@@ -51,7 +51,8 @@ namespace Avalonia.Skia
             _grContext = createInfo.GrContext;
             _gpu = createInfo.Gpu;
 
-            _surface = _gpu?.TryCreateSurface(PixelSize, createInfo.Session);
+            if (!createInfo.DisableManualFbo)
+                _surface = _gpu?.TryCreateSurface(PixelSize, createInfo.Session);
             if (_surface == null)
                 _surface = new SkiaSurfaceWrapper(CreateSurface(createInfo.GrContext, PixelSize.Width, PixelSize.Height,
                     createInfo.Format));
@@ -220,6 +221,8 @@ namespace Avalonia.Skia
             public ISkiaGpu Gpu;
 
             public ISkiaGpuRenderSession Session;
+
+            public bool DisableManualFbo;
         }
     }
 }