From e893705823862945c4cfa0316e77f8293817d59c Mon Sep 17 00:00:00 2001
From: Andrey Kunchev <donandren@gmail.com>
Date: Fri, 2 Oct 2020 16:07:38 +0300
Subject: [PATCH] add a way to render to canvas with DrawingContext with public
 api

---
 .../ExternalCanvasRenderTarget.cs             | 32 +++++++++++++++++++
 .../Avalonia.Skia/IExternalCanvasSurface.cs   | 11 +++++++
 .../Avalonia.Skia/PlatformRenderInterface.cs  |  2 ++
 3 files changed, 45 insertions(+)
 create mode 100644 src/Skia/Avalonia.Skia/ExternalCanvasRenderTarget.cs
 create mode 100644 src/Skia/Avalonia.Skia/IExternalCanvasSurface.cs

diff --git a/src/Skia/Avalonia.Skia/ExternalCanvasRenderTarget.cs b/src/Skia/Avalonia.Skia/ExternalCanvasRenderTarget.cs
new file mode 100644
index 0000000000..c9e779797b
--- /dev/null
+++ b/src/Skia/Avalonia.Skia/ExternalCanvasRenderTarget.cs
@@ -0,0 +1,32 @@
+using Avalonia.Platform;
+using Avalonia.Rendering;
+
+namespace Avalonia.Skia
+{
+    internal class ExternalCanvasRenderTarget : IRenderTarget
+    {
+        private IExternalCanvasSurface _surface;
+
+        public ExternalCanvasRenderTarget(IExternalCanvasSurface canvas)
+        {
+            _surface = canvas;
+        }
+
+        public IDrawingContextImpl CreateDrawingContext(IVisualBrushRenderer visualBrushRenderer)
+        {
+            var createInfo = new DrawingContextImpl.CreateInfo
+            {
+                Canvas = _surface.Canvas,
+                Dpi = _surface.Dpi,
+                VisualBrushRenderer = visualBrushRenderer,
+                DisableTextLcdRendering = true,
+            };
+
+            return new DrawingContextImpl(createInfo);
+        }
+
+        public void Dispose()
+        {
+        }
+    }
+}
diff --git a/src/Skia/Avalonia.Skia/IExternalCanvasSurface.cs b/src/Skia/Avalonia.Skia/IExternalCanvasSurface.cs
new file mode 100644
index 0000000000..38347f2caa
--- /dev/null
+++ b/src/Skia/Avalonia.Skia/IExternalCanvasSurface.cs
@@ -0,0 +1,11 @@
+using SkiaSharp;
+
+namespace Avalonia.Skia
+{
+    public interface IExternalCanvasSurface
+    {
+        SKCanvas Canvas { get; }
+
+        Vector Dpi { get; }
+    }
+}
diff --git a/src/Skia/Avalonia.Skia/PlatformRenderInterface.cs b/src/Skia/Avalonia.Skia/PlatformRenderInterface.cs
index b9c1cbc673..397d358ba7 100644
--- a/src/Skia/Avalonia.Skia/PlatformRenderInterface.cs
+++ b/src/Skia/Avalonia.Skia/PlatformRenderInterface.cs
@@ -145,6 +145,8 @@ namespace Avalonia.Skia
             {
                 if (surface is IFramebufferPlatformSurface framebufferSurface)
                     return new FramebufferRenderTarget(framebufferSurface);
+                if (surface is IExternalCanvasSurface canvas)
+                    return new ExternalCanvasRenderTarget(canvas);
             }
 
             throw new NotSupportedException(