feat: GLCanvasElement.LoadedSuccessfully

doc/articles/controls/GLCanvasElement.md

@@ -23,7 +23,7 @@ These three abstract methods take a `Silk.NET.OpenGL.GL` parameter that can be u
 
 ### The GLCanvasElement constructor
 
-The protected constructor requires a `Func<Window>` argument that fetches the `Microsoft.UI.Xaml.Window` object that the `GLCanvasElement` belongs to. This function is required because WinUI doesn't yet provide a way to get the `Window` of a `FrameworkElement`. This parameter is ignored on Uno Platform and must be set to null. This function is only called while the `GLCanvasElement` is still in the visual tree.
+The protected constructor requires a `Func<Window>` argument that fetches the `Microsoft.UI.Xaml.Window` object that the `GLCanvasElement` belongs to. This function is required because WinUI doesn't yet provide a way to get the `Window` of a `FrameworkElement`. This parameter is ignored on Uno Platform and can be set to null. This function is only called while the `GLCanvasElement` is still in the visual tree.
 
 ### The `Init` method
 
@@ -41,6 +41,10 @@ On MacOS, since OpenGL support is not natively present, we use [ANGLE](https://e
 
 Additionally, `GLCanvasElement` has an `Invalidate` method that requests a redrawing of the `GLCanvasElement`, calling `RenderOverride` in the process. Note that `RenderOverride` will only be called once per `Invalidate` call and the output will be saved to be used in future frames. To update the output, you must call `Invalidate`. If you need to continuously update the output (e.g. in an animation), you can add an `Invalidate` call inside `RenderOverride`.
 
+## Detecting errors
+
+To detect errors in initializing the OpenGL environment, `GLCanvasElement` exposes a `LoadedSuccessfully` property that shows whether or nor the loading of the element and its OpenGL setup were successful. This property is only valid when the element is loading, i.e. its `IsLoaded` property is true. When the element is not loaded, the value of `LoadedSuccessfully` will be null. 
+
 ## How to use Silk.NET
 
 To learn more about using [Silk.NET](https://www.nuget.org/packages/Silk.NET.OpenGL/) as a C# binding for OpenGL, see the examples in the Silk.NET repository [here](https://github.com/dotnet/Silk.NET/tree/main/examples/CSharp). Note that the windowing and inputs APIs in Silk.NET are not relevant to `GLCanvasElement`, since we only use Silk.NET as an OpenGL binding library, not a windowing library.

src/AddIns/Uno.WinUI.Graphics3DGL/GLCanvasElement.cs

@@ -20,7 +20,6 @@
 #endif
 
 #if WINAPPSDK
-using System.Runtime.InteropServices;
 using System.Runtime.InteropServices.WindowsRuntime;
 #else
 using Uno.Foundation.Extensibility;
@@ -41,19 +40,9 @@ namespace Uno.WinUI.Graphics3DGL;
 public abstract partial class GLCanvasElement : Grid, INativeContext
 {
 	private const int BytesPerPixel = 4;
-	private static readonly BitmapImage _fallbackImage = new BitmapImage(new Uri("ms-appx:///Assets/error.png"));
 	private static readonly Dictionary<XamlRoot, INativeOpenGLWrapper?> _xamlRootToWrapper = new();
 
-	private static (int major, int minor) _minVersion = (3, 0);
-
-	/// <summary>
-	/// The minimum required OpenGL version. Set this property depending on the OpenGL features you use.
-	/// </summary>
-	public static (int major, int minor) MinVersion
-	{
-		get => _minVersion;
-		set => _minVersion = value.major < 3 ? (3, 0) : value;
-	}
+	private static readonly (int major, int minor) _minVersion = (3, 0);
 
 	private readonly Func<Window>? _getWindowFunc;
 
@@ -111,8 +100,7 @@ protected GLCanvasElement(Func<Window>? getWindowFunc)
 
 		Background = new ImageBrush
 		{
-			RelativeTransform = new ScaleTransform { ScaleX = 1, ScaleY = -1, CenterX = 0.5, CenterY = 0.5 }, // because OpenGL coordinates go bottom-to-top
-			ImageSource = _fallbackImage
+			RelativeTransform = new ScaleTransform { ScaleX = 1, ScaleY = -1, CenterX = 0.5, CenterY = 0.5 } // because OpenGL coordinates go bottom-to-top
 		};
 
 		Loaded += OnLoaded;
@@ -159,7 +147,7 @@ protected GLCanvasElement(Func<Window>? getWindowFunc)
 					{
 						if (typeof(GLCanvasElement).Log().IsEnabled(LogLevel.Warning))
 						{
-							typeof(GLCanvasElement).Log().Warn($"{nameof(GLCanvasElement)} is using an ANGLE implementation, ignoring {nameof(MinVersion)} checks.");
+							typeof(GLCanvasElement).Log().Warn($"{nameof(GLCanvasElement)} is using an ANGLE implementation, ignoring minimum version checks.");
 						}
 					}
 					else
@@ -173,7 +161,7 @@ protected GLCanvasElement(Func<Window>? getWindowFunc)
 						{
 							if (typeof(GLCanvasElement).Log().IsEnabled(LogLevel.Error))
 							{
-								typeof(GLCanvasElement).Log().Error($"{nameof(GLCanvasElement)} requires at least {MinVersion.major}.{MinVersion.minor}, but found {major}.{minor}.");
+								typeof(GLCanvasElement).Log().Error($"{nameof(GLCanvasElement)} requires at least {_minVersion.major}.{_minVersion.minor}, but found {major}.{minor}.");
 							}
 
 							abort = true;
@@ -232,8 +220,16 @@ private void OnClosed(object _, object __)
 	public void Invalidate() => NativeDispatcher.Main.Enqueue(Render, NativeDispatcherPriority.Idle);
 #endif
 
+	/// <summary>
+	/// Indicates whether this element was loaded successfully or not, including the OpenGL context creation and setup.
+	/// This property is only valid when the element is loaded. When the element is not loaded, the value will be null.
+	/// </summary>
+	public bool? LoadedSuccessfully { get; private set; }
+
 	private void OnLoaded(object sender, RoutedEventArgs routedEventArgs)
 	{
+		LoadedSuccessfully = false;
+
 		_nativeOpenGlWrapper = GetOrCreateNativeOpenGlWrapper(XamlRoot!, _getWindowFunc);
 
 		if (_nativeOpenGlWrapper is null)
@@ -263,10 +259,13 @@ private void OnLoaded(object sender, RoutedEventArgs routedEventArgs)
 		{
 			fe.Unloaded += OnClosed;
 		}
+
+		LoadedSuccessfully = true;
 	}
 
 	private void OnUnloaded(object sender, RoutedEventArgs routedEventArgs)
 	{
+		LoadedSuccessfully = null;
 		if (_nativeOpenGlWrapper is null)
 		{
 			return;