Add gradient mesh support

samples/AvalonDraw/GradientMeshEditorWindow.axaml

@@ -0,0 +1,17 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        x:Class="AvalonDraw.GradientMeshEditorWindow"
+        Width="400" Height="300"
+        Title="Edit Gradient Mesh">
+    <Canvas x:Name="MeshCanvas" Background="Gray">
+        <ItemsControl ItemsSource="{Binding Points}">
+            <ItemsControl.ItemTemplate>
+                <DataTemplate>
+                    <Ellipse Width="10" Height="10" Fill="Red"
+                             Canvas.Left="{Binding Position.X}"
+                             Canvas.Top="{Binding Position.Y}" />
+                </DataTemplate>
+            </ItemsControl.ItemTemplate>
+        </ItemsControl>
+    </Canvas>
+</Window>

samples/AvalonDraw/GradientMeshEditorWindow.axaml.cs

@@ -0,0 +1,77 @@
+using System.Collections.ObjectModel;
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Input;
+using Avalonia.Markup.Xaml;
+using Avalonia.Media;
+using Svg.Model;
+
+namespace AvalonDraw;
+
+public partial class GradientMeshEditorWindow : Window
+{
+    private readonly Canvas _canvas;
+    private GradientMeshPoint? _dragging;
+
+    public ObservableCollection<GradientMeshPoint> Points { get; } = new();
+
+    public GradientMeshEditorWindow(GradientMesh mesh)
+    {
+        InitializeComponent();
+        _canvas = this.FindControl<Canvas>("MeshCanvas");
+        foreach (var p in mesh.Points)
+            Points.Add(p);
+        _canvas.PointerPressed += OnPointerPressed;
+        _canvas.PointerReleased += OnPointerReleased;
+        _canvas.PointerMoved += OnPointerMoved;
+        _canvas.DataContext = this;
+    }
+
+    private void InitializeComponent()
+    {
+        AvaloniaXamlLoader.Load(this);
+    }
+
+    private void OnPointerPressed(object? sender, PointerPressedEventArgs e)
+    {
+        var pos = e.GetPosition(_canvas);
+        foreach (var p in Points)
+        {
+            var rect = new Rect(p.Position.X - 5, p.Position.Y - 5, 10, 10);
+            if (rect.Contains(pos))
+            {
+                _dragging = p;
+                break;
+            }
+        }
+    }
+
+    private void OnPointerReleased(object? sender, PointerReleasedEventArgs e)
+    {
+        _dragging = null;
+    }
+
+    private void OnPointerMoved(object? sender, PointerEventArgs e)
+    {
+        if (_dragging is null)
+            return;
+
+        var pos = e.GetPosition(_canvas);
+        var index = Points.IndexOf(_dragging);
+        if (index >= 0)
+        {
+            Points[index] = _dragging with { Position = new ShimSkiaSharp.SKPoint((float)pos.X, (float)pos.Y) };
+            _dragging = Points[index];
+        }
+    }
+
+    public GradientMesh Result
+    {
+        get
+        {
+            var mesh = new GradientMesh();
+            mesh.Points.AddRange(Points);
+            return mesh;
+        }
+    }
+}

samples/AvalonDraw/MainWindow.axaml.cs

@@ -261,6 +261,16 @@ public MainWindow()
                 };
                 return picker;
             }
+            if (entry is GradientMeshEntry meshEntry)
+            {
+                var btn = new Button { Content = "Edit Mesh", VerticalAlignment = VerticalAlignment.Center };
+                btn.Click += async (_, _) =>
+                {
+                    var dlg = new GradientMeshEditorWindow(meshEntry.Mesh);
+                    await dlg.ShowDialog(this);
+                };
+                return btn;
+            }
             if (entry is GradientStopsEntry gEntry)
             {
                 var btn = new Button { Content = entry.Value ?? "Edit", VerticalAlignment = VerticalAlignment.Center };

samples/AvalonDraw/Services/GradientMeshEntry.cs

@@ -0,0 +1,20 @@
+using System;
+using Svg.Model;
+
+namespace AvalonDraw.Services;
+
+public class GradientMeshEntry : PropertyEntry
+{
+    public GradientMesh Mesh { get; }
+
+    public GradientMeshEntry(GradientMesh mesh)
+        : base("Mesh", string.Empty, (_, __) => { })
+    {
+        Mesh = mesh;
+    }
+
+    public override void Apply(object target)
+    {
+        // Placeholder for applying the mesh to an object.
+    }
+}

src/Svg.Model/GradientMesh.cs

@@ -0,0 +1,22 @@
+// Copyright (c) Wiesław Šoltés. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for details.
+using System.Collections.Generic;
+using ShimSkiaSharp;
+
+namespace Svg.Model;
+
+/// <summary>
+/// Represents a simple gradient mesh consisting of colored points.
+/// </summary>
+public sealed class GradientMesh
+{
+    /// <summary>
+    /// List of mesh points.
+    /// </summary>
+    public List<GradientMeshPoint> Points { get; } = new();
+}
+
+/// <summary>
+/// Defines a single mesh point with position and color.
+/// </summary>
+public sealed record GradientMeshPoint(SKPoint Position, SKColor Color);

src/Svg.Model/Services/GradientMeshService.cs

@@ -0,0 +1,35 @@
+// Copyright (c) Wiesław Šoltés. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for details.
+using System.Collections.Generic;
+using System.Linq;
+using ShimSkiaSharp;
+
+namespace Svg.Model.Services;
+
+/// <summary>
+/// Provides conversion helpers for <see cref="GradientMesh"/> instances.
+/// </summary>
+public static class GradientMeshService
+{
+    /// <summary>
+    /// Convert gradient mesh points to a mesh shader if supported. Currently this
+    /// implementation falls back to a linear gradient created between the first
+    /// and last mesh points when mesh shaders are not available.
+    /// </summary>
+    public static SKShader? ToShader(GradientMesh mesh)
+    {
+        if (mesh.Points.Count < 2)
+            return null;
+
+        // TODO: use mesh gradient when available in ShimSkiaSharp
+        var first = mesh.Points.First();
+        var last = mesh.Points.Last();
+        return SKShader.CreateLinearGradient(
+            first.Position,
+            last.Position,
+            new[] { (SKColorF)first.Color, (SKColorF)last.Color },
+            SKColorSpace.Srgb,
+            new[] { 0f, 1f },
+            SKShaderTileMode.Clamp);
+    }
+}