Do the manual blit if possible

src/Avalonia.OpenGL/GlInterface.cs

@@ -117,6 +117,19 @@ namespace Avalonia.OpenGL
         public delegate int GlCheckFramebufferStatus(int target);
         [GlEntryPoint("glCheckFramebufferStatus")]
         public GlCheckFramebufferStatus CheckFramebufferStatus { get; }
+
+        public delegate void GlBlitFramebuffer(int srcX0,
+            int srcY0,
+            int srcX1,
+            int srcY1,
+            int dstX0,
+            int dstY0,
+            int dstX1,
+            int dstY1,
+            int mask,
+            int filter);
+        [GlMinVersionEntryPoint("glBlitFramebuffer", 3, 0)]
+        public GlBlitFramebuffer BlitFramebuffer { get; }
         
         public delegate void GlGenRenderbuffers(int count, int[] res);
         [GlEntryPoint("glGenRenderbuffers")]

src/Skia/Avalonia.Skia/Gpu/ISkiaGpu.cs

@@ -28,7 +28,9 @@ namespace Avalonia.Skia
     {
         SKSurface WriteSurface { get; }
         SKSurface ReadSurface { get; }
-        
+        bool CanBlit { get; }
+        void Blit();
+
     }
 
     public interface IOpenGlAwareSkiaGpu : ISkiaGpu

src/Skia/Avalonia.Skia/Gpu/OpenGl/FboSkiaSurface.cs

@@ -97,15 +97,16 @@ namespace Avalonia.Skia
                 new GRGlFramebufferInfo((uint)_fbo, SKColorType.Rgba8888.ToGlSizedFormat()));
             WriteSurface = SKSurface.Create(_grContext, target,
                 GRSurfaceOrigin.BottomLeft, SKColorType.Rgba8888);
+            CanBlit = gl.BlitFramebuffer != null;
         }
         
         public void Dispose()
         {
             using (_glContext.EnsureCurrent())
             {
-                WriteSurface.Dispose();
+                WriteSurface?.Dispose();
                 WriteSurface = null;
-                ReadSurface.Dispose();
+                ReadSurface?.Dispose();
                 ReadSurface = null;
                 var gl = _glContext.GlInterface;
                 if (_fbo != 0)
@@ -120,5 +121,15 @@ namespace Avalonia.Skia
 
         public SKSurface WriteSurface { get; private set; }
         public SKSurface ReadSurface { get; private set; }
+        public bool CanBlit { get; }
+        public void Blit()
+        {
+            var gl = _glContext.GlInterface;
+            gl.GetIntegerv(GL_READ_FRAMEBUFFER_BINDING, out var oldRead);
+            gl.BindFramebuffer(GL_READ_FRAMEBUFFER, _fbo);
+            gl.BlitFramebuffer(0, 0, _pixelSize.Width, _pixelSize.Height, 0, 0, _pixelSize.Width, _pixelSize.Height,
+                GL_COLOR_BUFFER_BIT, GL_LINEAR);
+            gl.BindFramebuffer(GL_READ_FRAMEBUFFER, oldRead);
+        }
     }
 }

src/Skia/Avalonia.Skia/SurfaceRenderTarget.cs

@@ -23,6 +23,8 @@ namespace Avalonia.Skia
         {
             public SKSurface WriteSurface { get; private set; }
             public SKSurface ReadSurface { get; private set; }
+            public bool CanBlit => false;
+            public void Blit() => throw new NotSupportedException();
 
             public SkiaSurfaceWrapper(SKSurface surface)
             {
@@ -136,8 +138,12 @@ namespace Avalonia.Skia
         {
             if (sourceRect.Left == 0 && sourceRect.Top == 0 && sourceRect.Size == destRect.Size)
             {
-                _surface.ReadSurface.Canvas.Flush();
-                _surface.ReadSurface.Draw(context.Canvas, destRect.Left, destRect.Top, paint);
+                _surface.WriteSurface.Canvas.Flush();
+                if (context.Canvas.TotalMatrix.IsIdentity && _surface.CanBlit && destRect.Top == 0 &&
+                    destRect.Left == 0)
+                    _surface.Blit();
+                else
+                    _surface.ReadSurface.Draw(context.Canvas, destRect.Left, destRect.Top, paint);
             }
             else
                 using (var image = SnapshotImage())