Fix iOS OpenGL rendering with newer Skia

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

@@ -69,6 +69,7 @@ namespace Avalonia.Skia
                 gl.GetIntegerv(GL_FRAMEBUFFER_BINDING, out var fb);
 
                 var size = glSession.Size;
+                var colorType = SKColorType.Rgba8888;
                 var scaling = glSession.Scaling;
                 if (size.Width <= 0 || size.Height <= 0 || scaling < 0)
                 {
@@ -81,12 +82,16 @@ namespace Avalonia.Skia
                 {
                     _grContext.ResetContext();
 
-                    var renderTarget =
-                        new GRBackendRenderTarget(size.Width, size.Height, disp.SampleCount, disp.StencilSize,
-                            new GRGlFramebufferInfo((uint)fb, SKColorType.Rgba8888.ToGlSizedFormat()));
+                    var samples = disp.SampleCount;
+                    var maxSamples = _grContext.GetMaxSurfaceSampleCount(colorType);
+                    if (samples > maxSamples)
+                        samples = maxSamples;
+
+                    var glInfo = new GRGlFramebufferInfo((uint)fb, colorType.ToGlSizedFormat());
+                    var renderTarget = new GRBackendRenderTarget(size.Width, size.Height, samples, disp.StencilSize, glInfo);
                     var surface = SKSurface.Create(_grContext, renderTarget,
                         glSession.IsYFlipped ? GRSurfaceOrigin.TopLeft : GRSurfaceOrigin.BottomLeft,
-                        SKColorType.Rgba8888);
+                        colorType);
 
                     success = true;
 

src/iOS/Avalonia.iOS/EaglDisplay.cs

@@ -74,7 +74,21 @@ namespace Avalonia.iOS
 
         public GlVersion Version { get; } = new GlVersion(GlProfileType.OpenGLES, 3, 0);
         public GlInterface GlInterface { get; }
-        public int SampleCount { get; } = 0;
-        public int StencilSize { get; } = 9;
+        public int SampleCount
+        {
+            get
+            {
+                GlInterface.GetIntegerv(GlConsts.GL_SAMPLES, out var samples);
+                return samples;
+            }
+        }
+        public int StencilSize
+        {
+            get
+            {
+                GlInterface.GetIntegerv(GlConsts.GL_STENCIL_BITS, out var stencil);
+                return stencil;
+            }
+        }
     }
 }