Make Avalonia.Skia compatible with both SkiaSharp 2.88 and 3.0 (#14510)

* Add missing AvsCurrentTargetFramework on Skia project

* Implement SkiaCompat using UnsafeAccessor and cached functon pointer

* Do not support SkiaSharp 3.0 on older targest, avoiding reflection completely

* Make SkiaCompat static initialization more consistent

* Remove function pointers completely

---------

Co-authored-by: Nikita Tsukanov <keks9n@gmail.com>

src/Skia/Avalonia.Skia/Avalonia.Skia.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(AvsLegacyTargetFrameworks);netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>$(AvsCurrentTargetFramework);$(AvsLegacyTargetFrameworks);netstandard2.0</TargetFrameworks>
     <IncludeLinuxSkia>true</IncludeLinuxSkia>
     <IncludeWasmSkia>true</IncludeWasmSkia>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>

src/Skia/Avalonia.Skia/Compatibility/SkiaCompat.SKCanvas.cs

@@ -0,0 +1,34 @@
+using System;
+using System.Runtime.CompilerServices;
+using SkiaSharp;
+
+namespace Avalonia.Skia;
+
+internal static partial class SkiaCompat
+{
+    public static void SetMatrix(SKCanvas canvas, in SKMatrix matrix)
+    {
+        if (s_isSkiaSharp3)
+        {
+#if NET8_0_OR_GREATER
+            NewCanvasSetMatrix(canvas, matrix);
+#else
+            throw UnsupportedException();
+#endif
+        }
+        else
+        {
+            LegacyCall(canvas, matrix);
+
+            static void LegacyCall(SKCanvas canvas, in SKMatrix matrix)
+            {
+                canvas.SetMatrix(matrix);
+            }
+        }
+    }
+
+#if NET8_0_OR_GREATER
+    [UnsafeAccessor(UnsafeAccessorKind.Method, Name = "SetMatrix")]
+    private static extern void NewCanvasSetMatrix(SKCanvas canvas, in SKMatrix matrix);
+#endif
+}

src/Skia/Avalonia.Skia/Compatibility/SkiaCompat.SKImageFilter.cs

@@ -0,0 +1,57 @@
+using System;
+using System.Runtime.CompilerServices;
+using SkiaSharp;
+
+namespace Avalonia.Skia;
+
+internal static partial class SkiaCompat
+{
+    public static SKImageFilter CreateBlur(float sigmaX, float sigmaY)
+    {
+        if (s_isSkiaSharp3)
+        {
+#if NET8_0_OR_GREATER
+            return NewSKImageFilterCreateBlur(null, sigmaX, sigmaY);
+#else
+            throw UnsupportedException();
+#endif
+        }
+        else
+        {
+            return LegacyBlurCall(sigmaX, sigmaY);
+
+            static SKImageFilter LegacyBlurCall(float sigmaX, float sigmaY) =>
+                SKImageFilter.CreateBlur(sigmaX, sigmaY);
+        }
+    }
+
+    public static SKImageFilter CreateDropShadow(float dropOffsetX, float dropOffsetY, float sigma, float f,
+        SKColor color)
+    {
+        if (s_isSkiaSharp3)
+        {
+#if NET8_0_OR_GREATER
+            return NewSKImageFilterCreateDropShadow(null!, dropOffsetX, dropOffsetY, sigma, f, color);
+#else
+            throw UnsupportedException();
+#endif
+        }
+        else
+        {
+            return LegacyDropShadowCall(dropOffsetX, dropOffsetY, sigma, f, color);
+
+            static SKImageFilter LegacyDropShadowCall(float dropOffsetX, float dropOffsetY, float sigma, float f, SKColor color) =>
+                SKImageFilter.CreateDropShadow(dropOffsetX, dropOffsetY, sigma, f, color);
+        }
+    }
+
+#if NET8_0_OR_GREATER
+    // See https://github.com/dotnet/runtime/issues/90081 why we need `SKImageFilter _`
+    [UnsafeAccessor(UnsafeAccessorKind.StaticMethod, Name = "CreateBlur")]
+    private static extern SKImageFilter NewSKImageFilterCreateBlur(SKImageFilter? _, float sigmaX, float sigmaY);
+
+    [UnsafeAccessor(UnsafeAccessorKind.StaticMethod, Name = "CreateDropShadow")]
+    private static extern SKImageFilter NewSKImageFilterCreateDropShadow(SKImageFilter? _, float dropOffsetX,
+        float dropOffsetY, float sigma, float f, SKColor color);
+#endif
+}

src/Skia/Avalonia.Skia/Compatibility/SkiaCompat.SKPath.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Runtime.CompilerServices;
+using SkiaSharp;
+
+namespace Avalonia.Skia;
+
+internal static partial class SkiaCompat
+{
+    public static void Transform(SKPath path, in SKMatrix matrix)
+    {
+        if (s_isSkiaSharp3)
+        {
+#if NET8_0_OR_GREATER
+            NewPathTransform(path, matrix);
+#else
+            throw UnsupportedException();
+#endif
+        }
+        else
+        {
+            LegacyCall(path, matrix);
+
+            static void LegacyCall(SKPath path, in SKMatrix matrix) =>
+                path.Transform(matrix);
+        }
+    }
+
+#if NET8_0_OR_GREATER
+    [UnsafeAccessor(UnsafeAccessorKind.Method, Name = "Transform")]
+    private static extern void NewPathTransform(SKPath path, in SKMatrix matrix);
+#endif
+}

src/Skia/Avalonia.Skia/Compatibility/SkiaCompat.cs

@@ -0,0 +1,16 @@
+using System;
+using SkiaSharp;
+
+namespace Avalonia.Skia;
+
+internal static partial class SkiaCompat
+{
+    private static readonly bool s_isSkiaSharp3 = typeof(SKPaint).Assembly.GetName().Version?.Major == 3;
+
+#if !NET8_0_OR_GREATER
+    private static Exception UnsupportedException()
+    {
+        return new InvalidOperationException("Avalonia doesn't support SkiaSharp 3.0 on .NET 7 and older. Please upgrade to .NET 8.");
+    }
+#endif
+}

src/Skia/Avalonia.Skia/DrawingContextImpl.Effects.cs

@@ -30,7 +30,7 @@ partial class DrawingContextImpl
             if (blur.Radius <= 0)
                 return null;
             var sigma = SkBlurRadiusToSigma(blur.Radius);
-            return SKImageFilter.CreateBlur(sigma, sigma);
+            return SkiaCompat.CreateBlur(sigma, sigma);
         }
 
         if (effect is IDropShadowEffect drop)
@@ -41,7 +41,7 @@ partial class DrawingContextImpl
                 alpha *= _currentOpacity;
             var color = new SKColor(drop.Color.R, drop.Color.G, drop.Color.B, (byte)Math.Max(0, Math.Min(255, alpha)));
 
-            return SKImageFilter.CreateDropShadow((float)drop.OffsetX, (float)drop.OffsetY, sigma, sigma, color);
+            return SkiaCompat.CreateDropShadow((float)drop.OffsetX, (float)drop.OffsetY, sigma, sigma, color);
         }
 
         return null;

src/Skia/Avalonia.Skia/DrawingContextImpl.cs

@@ -139,7 +139,7 @@ namespace Avalonia.Skia
                 {
                     if (!_isDisposed)
                     {
-                        _context.Canvas.SetMatrix(_revertTransform);
+                        SkiaCompat.SetMatrix(_context.Canvas, _revertTransform);
                         _context._leased = false;
                         _isDisposed = true;
                     }
@@ -328,7 +328,7 @@ namespace Avalonia.Skia
             {
                 var ac = shadow.Color;
 
-                var filter = SKImageFilter.CreateBlur(SkBlurRadiusToSigma(shadow.Blur), SkBlurRadiusToSigma(shadow.Blur));
+                var filter = SkiaCompat.CreateBlur(SkBlurRadiusToSigma(shadow.Blur), SkBlurRadiusToSigma(shadow.Blur));
                 var color = new SKColor(ac.R, ac.G, ac.B, (byte)(ac.A * opacity));
 
                 paint.Reset();
@@ -853,7 +853,7 @@ namespace Avalonia.Skia
                     transform *= _postTransform.Value;
                 }
 
-                Canvas.SetMatrix(transform.ToSKMatrix());
+                SkiaCompat.SetMatrix(Canvas, transform.ToSKMatrix());
             }
         }
 

src/Skia/Avalonia.Skia/SurfaceRenderTarget.cs

@@ -157,7 +157,7 @@ namespace Avalonia.Skia
                 var oldMatrix = context.Canvas.TotalMatrix;
                 context.Canvas.ResetMatrix();
                 _surface.Surface.Draw(context.Canvas, 0, 0, null);
-                context.Canvas.SetMatrix(oldMatrix);
+                SkiaCompat.SetMatrix(context.Canvas, oldMatrix);
             }
         }
 

src/Skia/Avalonia.Skia/TransformedGeometryImpl.cs

@@ -20,8 +20,9 @@ namespace Avalonia.Skia
             var matrix = transform.ToSKMatrix();
 
             var transformedPath = StrokePath =  source.StrokePath.Clone();
-            transformedPath?.Transform(matrix);
+            if (transformedPath is not null)
-            
+                SkiaCompat.Transform(transformedPath, matrix);
+
             Bounds = transformedPath?.TightBounds.ToAvaloniaRect() ?? default;
             
             if (ReferenceEquals(source.StrokePath, source.FillPath))
@@ -29,7 +30,7 @@ namespace Avalonia.Skia
             else if (source.FillPath != null)
             {
                 FillPath = transformedPath = source.FillPath.Clone();
-                transformedPath.Transform(matrix);
+                SkiaCompat.Transform(transformedPath, matrix);
             }
         }