Reduce EAGL related warnings in iOS project (#13730)

src/iOS/Avalonia.iOS/AvaloniaView.cs

@@ -2,6 +2,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Runtime.Versioning;
 using Avalonia.Controls;
 using Avalonia.Controls.Embedding;
 using Avalonia.Controls.Platform;
@@ -46,6 +47,15 @@ namespace Avalonia.iOS
 
             _topLevel.StartRendering();
 
+            InitEagl();
+            MultipleTouchEnabled = true;
+        }
+
+        [ObsoletedOSPlatform("ios12.0", "Use 'Metal' instead.")]
+        [SupportedOSPlatform("ios")]
+        [UnsupportedOSPlatform("maccatalyst")]
+        private void InitEagl()
+        {
             var l = (CAEAGLLayer)Layer;
             l.ContentsScale = UIScreen.MainScreen.Scale;
             l.Opaque = true;
@@ -54,7 +64,6 @@ namespace Avalonia.iOS
                 EAGLDrawableProperty.ColorFormat, EAGLColorFormat.RGBA8
             );
             _topLevelImpl.Surfaces = new[] { new EaglLayerSurface(l) };
-            MultipleTouchEnabled = true;
         }
 
         /// <inheritdoc />

src/iOS/Avalonia.iOS/EaglDisplay.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Runtime.Versioning;
 using Avalonia.OpenGL;
 using Avalonia.Platform;
 using Avalonia.Reactive;
@@ -7,6 +8,8 @@ using OpenGLES;
 
 namespace Avalonia.iOS
 {
+    [ObsoletedOSPlatform("ios12.0", "Use 'Metal' instead.")]
+    [SupportedOSPlatform("ios")]
     class EaglPlatformGraphics : IPlatformGraphics
     {
         public IPlatformGraphicsContext GetSharedContext() => Context;
@@ -28,6 +31,8 @@ namespace Avalonia.iOS
         }
     }
 
+    [ObsoletedOSPlatform("ios12.0", "Use 'Metal' instead.")]
+    [SupportedOSPlatform("ios")]
     class GlContext : IGlContext
     {
         public EAGLContext Context { get; private set; }

src/iOS/Avalonia.iOS/EaglLayerSurface.cs

@@ -1,5 +1,6 @@
 
 using System;
+using System.Runtime.Versioning;
 using System.Threading;
 using Avalonia.OpenGL;
 using Avalonia.OpenGL.Surfaces;
@@ -7,6 +8,8 @@ using CoreAnimation;
 
 namespace Avalonia.iOS
 {
+    [ObsoletedOSPlatform("ios12.0", "Use 'Metal' instead.")]
+    [SupportedOSPlatform("ios")]
     class EaglLayerSurface : IGlPlatformSurface
     {
         private readonly CAEAGLLayer _layer;

src/iOS/Avalonia.iOS/LayerFbo.cs

@@ -1,10 +1,13 @@
 using System;
+using System.Runtime.Versioning;
 using Avalonia.OpenGL;
 using CoreAnimation;
 using OpenGLES;
 
 namespace Avalonia.iOS
 {
+    [ObsoletedOSPlatform("ios12.0", "Use 'Metal' instead.")]
+    [SupportedOSPlatform("ios")]
     internal class LayerFbo
     {
         private readonly EAGLContext _context;
@@ -90,6 +93,8 @@ namespace Avalonia.iOS
         }
     }
 
+    [ObsoletedOSPlatform("ios12.0", "Use 'Metal' instead.")]
+    [SupportedOSPlatform("ios")]
     class SizeSynchronizedLayerFbo : IDisposable
     {
         private readonly EAGLContext _context;

src/iOS/Avalonia.iOS/Platform.cs

@@ -38,7 +38,7 @@ namespace Avalonia.iOS
             var keyboard = new KeyboardDevice();
 
             AvaloniaLocator.CurrentMutable
-                .Bind<IPlatformGraphics>().ToConstant(GlFeature)
+                .Bind<IPlatformGraphics>().ToConstant((IPlatformGraphics) GlFeature)
                 .Bind<ICursorFactory>().ToConstant(new CursorFactoryStub())
                 .Bind<IWindowingPlatform>().ToConstant(new WindowingPlatformStub())
                 .Bind<IPlatformSettings>().ToSingleton<PlatformSettings>()

src/iOS/Avalonia.iOS/Properties/AssemblyInfo.cs

@@ -0,0 +1,4 @@
+using System.Runtime.Versioning;
+
+// Remove spurious warnings for maccatalyst (which isn't targeted): https://github.com/dotnet/roslyn-analyzers/issues/6269
+[assembly: UnsupportedOSPlatform("maccatalyst")]