Add RadialGradientBrush support for Direct2D and Cairo backend.

src/Gtk/Perspex.Cairo/Media/DrawingContext.cs

@@ -254,6 +254,7 @@ namespace Perspex.Cairo.Media
 
             var solid = brush as SolidColorBrush;
             var linearGradientBrush = brush as LinearGradientBrush;
+            var radialGradientBrush = brush as RadialGradientBrush;
             var imageBrush = brush as ImageBrush;
             var visualBrush = brush as VisualBrush;
 			BrushImpl impl = null;
@@ -265,8 +266,12 @@ namespace Perspex.Cairo.Media
 			else if (linearGradientBrush != null) 
 			{
 				impl = new LinearGradientBrushImpl(linearGradientBrush, destinationSize);
-			} 
-			else if (imageBrush != null) 
+			}
+            else if (radialGradientBrush != null)
+            {
+                impl = new RadialGradientBrushImpl(radialGradientBrush, destinationSize);
+            }
+            else if (imageBrush != null) 
 			{
 				impl = new ImageBrushImpl(imageBrush, destinationSize);
 			} 

src/Gtk/Perspex.Cairo/Media/RadialGradientBrushImpl.cs

@@ -0,0 +1,25 @@
+using System;
+using global::Cairo;
+
+namespace Perspex.Cairo
+{
+	public class RadialGradientBrushImpl : BrushImpl
+	{
+		public RadialGradientBrushImpl(Perspex.Media.RadialGradientBrush brush, Size destinationSize)
+		{
+			var center = brush.Center.ToPixels(destinationSize);
+			var gradientOrigin = brush.GradientOrigin.ToPixels(destinationSize);
+            var radius = brush.Radius;
+
+			this.PlatformBrush = new RadialGradient(center.X, center.Y, radius, gradientOrigin.X, gradientOrigin.Y, radius);
+
+            foreach (var stop in brush.GradientStops)
+            {
+                ((LinearGradient)this.PlatformBrush).AddColorStop(stop.Offset, stop.Color.ToCairo());
+            }
+
+			((LinearGradient)this.PlatformBrush).Extend = Extend.Pad;
+		}
+	}
+}
+

src/Gtk/Perspex.Cairo/Perspex.Cairo.csproj

@@ -61,6 +61,7 @@
     <Compile Include="Media\FormattedTextImpl.cs" />
     <Compile Include="Media\Imaging\BitmapImpl.cs" />
     <Compile Include="Media\Imaging\RenderTargetBitmapImpl.cs" />
+    <Compile Include="Media\RadialGradientBrushImpl.cs" />
     <Compile Include="Media\TileBrushes.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="Renderer.cs" />
@@ -103,4 +104,4 @@
   <Target Name="AfterBuild">
   </Target>
   -->
-</Project>
+</Project>

src/Perspex.SceneGraph/Media/LinearGradientBrush.cs

@@ -6,7 +6,7 @@ namespace Perspex.Media
     /// <summary>
     /// A brush that draws with a linear gradient.
     /// </summary>
-    public class LinearGradientBrush : GradientBrush
+    public sealed class LinearGradientBrush : GradientBrush
     {
         /// <summary>
         /// Defines the <see cref="StartPoint"/> property.

src/Perspex.SceneGraph/Media/RadialGradientBrush.cs

@@ -0,0 +1,63 @@
+// Copyright (c) The Perspex Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+namespace Perspex.Media
+{
+    /// <summary>
+    /// Paints an area with a radial gradient. A focal point defines the beginning of the gradient, 
+    /// and a circle defines the end point of the gradient.
+    /// </summary>
+    public sealed class RadialGradientBrush : GradientBrush
+    {
+        /// <summary>
+        /// Defines the <see cref="Center"/> property.
+        /// </summary>
+        public static readonly PerspexProperty<RelativePoint> CenterProperty =
+            PerspexProperty.Register<RadialGradientBrush, RelativePoint>(
+                nameof(Center),
+                RelativePoint.Center);
+
+        /// <summary>
+        /// Defines the <see cref="GradientOrigin"/> property.
+        /// </summary>
+        public static readonly PerspexProperty<RelativePoint> GradientOriginProperty =
+            PerspexProperty.Register<RadialGradientBrush, RelativePoint>(
+                nameof(GradientOrigin), 
+                RelativePoint.Center);
+
+        /// <summary>
+        /// Defines the <see cref="Radius"/> property.
+        /// </summary>
+        public static readonly PerspexProperty<double> RadiusProperty =
+            PerspexProperty.Register<RadialGradientBrush, double>(
+                nameof(Radius),
+                0.5);
+
+        /// <summary>
+        /// Gets or sets the start point for the gradient.
+        /// </summary>
+        public RelativePoint Center
+        {
+            get { return GetValue(CenterProperty); }
+            set { SetValue(CenterProperty, value); }
+        }
+
+        /// <summary>
+        /// Gets or sets the location of the two-dimensional focal point that defines the beginning of the gradient.
+        /// </summary>
+        public RelativePoint GradientOrigin
+        {
+            get { return GetValue(GradientOriginProperty); }
+            set { SetValue(GradientOriginProperty, value); }
+        }
+
+        /// <summary>
+        ///  ets or sets the horizontal and vertical radius of the outermost circle of the radial gradient.
+        /// </summary>
+        public double Radius
+        {
+            get { return GetValue(RadiusProperty); }
+            set { SetValue(RadiusProperty, value); }
+        }
+    }
+}

src/Perspex.SceneGraph/Perspex.SceneGraph.csproj

@@ -67,6 +67,7 @@
     <Compile Include="Media\GradientBrush.cs" />
     <Compile Include="Media\GradientSpreadMethod.cs" />
     <Compile Include="Media\GradientStop.cs" />
+    <Compile Include="Media\RadialGradientBrush.cs" />
     <Compile Include="Media\LinearGradientBrush.cs" />
     <Compile Include="Media\MediaExtensions.cs" />
     <Compile Include="Media\PenLineCap.cs" />

src/Windows/Perspex.Direct2D1/Media/DrawingContext.cs

@@ -303,6 +303,7 @@ namespace Perspex.Direct2D1.Media
         {
             var solidColorBrush = brush as Perspex.Media.SolidColorBrush;
             var linearGradientBrush = brush as Perspex.Media.LinearGradientBrush;
+            var radialGradientBrush = brush as Perspex.Media.RadialGradientBrush;
             var imageBrush = brush as ImageBrush;
             var visualBrush = brush as VisualBrush;
 
@@ -314,6 +315,10 @@ namespace Perspex.Direct2D1.Media
             {
                 return new LinearGradientBrushImpl(linearGradientBrush, _renderTarget, destinationSize);
             }
+            else if (radialGradientBrush != null)
+            {
+                return new RadialGradientBrushImpl(radialGradientBrush, _renderTarget, destinationSize);
+            }
             else if (imageBrush != null)
             {
                 return new ImageBrushImpl(imageBrush, _renderTarget, destinationSize);

src/Windows/Perspex.Direct2D1/Media/RadialGradientBrushImpl.cs

@@ -0,0 +1,38 @@
+// Copyright (c) The Perspex Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Perspex.Direct2D1.Media
+{
+    public class RadialGradientBrushImpl : BrushImpl
+    {
+        public RadialGradientBrushImpl(
+            Perspex.Media.RadialGradientBrush brush,
+            SharpDX.Direct2D1.RenderTarget target,
+            Size destinationSize)
+        {
+            if (brush != null)
+            {
+                var gradientStops = brush.GradientStops.Select(s => new SharpDX.Direct2D1.GradientStop { Color = s.Color.ToDirect2D(), Position = (float)s.Offset }).ToArray();
+
+                Point centerPoint = brush.Center.ToPixels(destinationSize);
+                Point GradientOriginOffset = brush.GradientOrigin.ToPixels(destinationSize);
+                // Note: Direct2D supports RadiusX and RadiusY but Cairo backend supports only Radius property
+                double radiusX = brush.Radius;
+                double radiusY = brush.Radius;
+
+                PlatformBrush = new SharpDX.Direct2D1.RadialGradientBrush(
+                    target,
+                    new SharpDX.Direct2D1.RadialGradientBrushProperties { Center = centerPoint.ToSharpDX(), GradientOriginOffset = GradientOriginOffset.ToSharpDX(), RadiusX = (float)radiusX, RadiusY = (float)radiusY },
+                    new SharpDX.Direct2D1.BrushProperties { Opacity = (float)brush.Opacity, Transform = target.Transform },
+                    new SharpDX.Direct2D1.GradientStopCollection(target, gradientStops, brush.SpreadMethod.ToDirect2D())
+                );
+            }
+        }
+    }
+}

src/Windows/Perspex.Direct2D1/Perspex.Direct2D1.csproj

@@ -79,6 +79,7 @@
     <Compile Include="Media\DrawingContext.cs" />
     <Compile Include="Media\Imaging\RenderTargetBitmapImpl.cs" />
     <Compile Include="Media\Imaging\BitmapImpl.cs" />
+    <Compile Include="Media\RadialGradientBrushImpl.cs" />
     <Compile Include="Media\LinearGradientBrushImpl.cs" />
     <Compile Include="Media\PerspexTextRenderer.cs" />
     <Compile Include="Media\ImageBrushImpl.cs" />