Use rendering mode

src/Avalonia.Native/AvaloniaNativePlatform.cs

@@ -123,40 +123,45 @@ namespace Avalonia.Native
             hotkeys.MoveCursorToTheEndOfLineWithSelection.Add(new KeyGesture(Key.Right, hotkeys.CommandModifiers | hotkeys.SelectionModifiers));
 
             AvaloniaLocator.CurrentMutable.Bind<PlatformHotkeyConfiguration>().ToConstant(hotkeys);
-            
-            if (_options.UseGpu)
+
+            foreach (var mode in _options.RenderingMode)
             {
-                if (_options.UseMetal)
+                if (mode == AvaloniaNativeRenderingMode.OpenGl)
                 {
                     try
                     {
-                        var metal = new MetalPlatformGraphics(_factory);
-                        metal.CreateContext().Dispose();
-                        _platformGraphics = metal;
+                        _platformGraphics = new AvaloniaNativeGlPlatformGraphics(_factory.ObtainGlDisplay());
+                        break;
                     }
-                    catch
+                    catch (Exception)
                     {
-                        // Ignored
+                        // ignored
                     }
                 }
-
-                if (_platformGraphics == null)
+#pragma warning disable CS0618
+                else if (mode == AvaloniaNativeRenderingMode.Metal)
+#pragma warning restore CS0618
                 {
                     try
                     {
-                        _platformGraphics = new AvaloniaNativeGlPlatformGraphics(_factory.ObtainGlDisplay());
+                        var metal = new MetalPlatformGraphics(_factory);
+                        metal.CreateContext().Dispose();
+                        _platformGraphics = metal;
                     }
-                    catch (Exception)
+                    catch
                     {
-                        // ignored
+                        // Ignored
                     }
                 }
-
-                if(_platformGraphics != null)
-                    AvaloniaLocator.CurrentMutable
-                        .Bind<IPlatformGraphics>().ToConstant(_platformGraphics);
+                else if (mode == AvaloniaNativeRenderingMode.Software)
+                    break;
             }
 
+            if (_platformGraphics != null)
+                AvaloniaLocator.CurrentMutable
+                    .Bind<IPlatformGraphics>().ToConstant(_platformGraphics);
+            
+
             Compositor = new Compositor(_platformGraphics, true);
         }
 

src/Avalonia.Native/AvaloniaNativePlatformExtensions.cs

@@ -26,18 +26,44 @@ namespace Avalonia
         }
     }
 
+    public enum AvaloniaNativeRenderingMode
+    {
+        /// <summary>
+        /// Avalonia would try to use native OpenGL with GPU rendering.
+        /// </summary>
+        OpenGl = 1,
+        /// <summary>
+        /// Avalonia is rendered into a framebuffer.
+        /// </summary>
+        Software = 2,
+        /// <summary>
+        /// Avalonia would try to use Metal with GPU rendering.
+        /// </summary>
+        [Obsolete("Experimental, unstable, not for production usage")]
+        Metal = 3
+    }
+    
     /// <summary>
     /// OSX backend options.
     /// </summary>
     public class AvaloniaNativePlatformOptions
     {
         /// <summary>
-        /// Determines whether to use GPU for rendering in your project. The default value is true.
+        /// Gets or sets Avalonia rendering modes with fallbacks.
+        /// The first element in the array has the highest priority.
+        /// The default value is: <see cref="AvaloniaNativeRenderingMode.OpenGl"/>, <see cref="AvaloniaNativeRenderingMode.Software"/>.
         /// </summary>
-        public bool UseGpu { get; set; } = true;
-
-        public bool UseMetal { get; set; }
-
+        /// <remarks>
+        /// If application should work on as wide range of devices as possible,
+        /// at least add <see cref="AvaloniaNativeRenderingMode.Software"/> as a fallback value.
+        /// </remarks>
+        /// <exception cref="System.InvalidOperationException">Thrown if no values were matched.</exception>
+        public IReadOnlyList<AvaloniaNativeRenderingMode> RenderingMode { get; set; } = new[]
+        {
+            AvaloniaNativeRenderingMode.OpenGl,
+            AvaloniaNativeRenderingMode.Software
+        };
+        
         /// <summary>
         /// Embeds popups to the window when set to true. The default value is false.
         /// </summary>