沿环形路径创建渐变画笔

<Window
    x:Class="WpfApp5.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:local="clr-namespace:WpfApp5"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:sys="clr-namespace:System;assembly=mscorlib"
    Title="MainWindow"
    Width="800"
    Height="450"
    mc:Ignorable="d">
    <Canvas x:Name="LayoutRoot">
        <Canvas.Resources>
            <x:Array x:Key="sampleData" Type="sys:Object">
                <x:Array Type="sys:Object">
                    <sys:Double>0</sys:Double>
                    <LinearGradientBrush StartPoint="0,0" EndPoint="1,0">
                        <GradientStop Offset="0" Color="Red" />
                        <GradientStop Offset="0.5" Color="Yellow" />
                        <GradientStop Offset="1" Color="Blue" />
                    </LinearGradientBrush>
                </x:Array>
                <x:Array Type="sys:Object">
                    <sys:Double>90</sys:Double>
                    <LinearGradientBrush StartPoint="0,0" EndPoint="1,0">
                        <GradientStop Offset="0" Color="Blue" />
                        <GradientStop Offset="0.5" Color="Green" />
                        <GradientStop Offset="1" Color="Red" />
                    </LinearGradientBrush>
                </x:Array>
                <x:Array Type="sys:Object">
                    <sys:Double>180</sys:Double>
                    <LinearGradientBrush StartPoint="0,0" EndPoint="1,0">
                        <GradientStop Offset="0" Color="Red" />
                        <GradientStop Offset="0.5" Color="Yellow" />
                        <GradientStop Offset="1" Color="Blue" />
                    </LinearGradientBrush>
                </x:Array>
                <x:Array Type="sys:Object">
                    <sys:Double>270</sys:Double>
                    <LinearGradientBrush StartPoint="0,0" EndPoint="1,0">
                        <GradientStop Offset="0" Color="Blue" />
                        <GradientStop Offset="0.5" Color="Green" />
                        <GradientStop Offset="1" Color="Red" />
                    </LinearGradientBrush>
                </x:Array>
            </x:Array>
        </Canvas.Resources>
        <ItemsControl ItemsSource="{StaticResource sampleData}">
            <ItemsControl.OpacityMask>
                <RadialGradientBrush>
                    <GradientStop Offset="0.95" Color="Transparent" />
                    <GradientStop Offset="0.949" Color="White" />
                    <GradientStop Offset="0.501" Color="White" />
                    <GradientStop Offset="0.5" Color="Transparent" />
                </RadialGradientBrush>
            </ItemsControl.OpacityMask>
            <ItemsControl.Template>
                <ControlTemplate TargetType="ItemsControl">
                    <ItemsPresenter />
                </ControlTemplate>
            </ItemsControl.Template>
            <ItemsControl.ItemsPanel>
                <ItemsPanelTemplate>
                    <Canvas />
                </ItemsPanelTemplate>
            </ItemsControl.ItemsPanel>
            <ItemsControl.ItemTemplate>
                <DataTemplate>
                    <Canvas Width="1" Height="1">
                        <Canvas.RenderTransform>
                            <RotateTransform Angle="{Binding [0]}" CenterX="124" CenterY="124" />
                        </Canvas.RenderTransform>
                        <Viewport3D Width="250" Height="250">
                            <ModelVisual3D>
                                <ModelVisual3D.Content>
                                    <Model3DGroup>
                                        <GeometryModel3D>
                                            <GeometryModel3D.Geometry>
                                                <MeshGeometry3D
                                                    Positions="0 0 0, 0 1 0, 1 0 0, 1 1 0"
                                                    TextureCoordinates="0 1, 0 0, 1 1, 1 0"
                                                    TriangleIndices="0 2 1, 2 3 1" />
                                            </GeometryModel3D.Geometry>
                                            <GeometryModel3D.Material>
                                                <DiffuseMaterial Brush="{Binding [1]}" />
                                            </GeometryModel3D.Material>
                                            <GeometryModel3D.Transform>
                                                <MatrixTransform3D Matrix="0.002,0,0,0,-0.499,-0.498,0,-0.998,0,0,1,0,0.499,0.5,0,1" />
                                            </GeometryModel3D.Transform>
                                        </GeometryModel3D>
                                        <AmbientLight Color="White" />
                                    </Model3DGroup>
                                </ModelVisual3D.Content>
                            </ModelVisual3D>
                            <Viewport3D.Camera>
                                <OrthographicCamera
                                    Width="1"
                                    LookDirection="0 0 -1"
                                    Position="0.5 0.5 1"
                                    UpDirection="0 1 0" />
                            </Viewport3D.Camera>
                        </Viewport3D>
                    </Canvas>
                </DataTemplate>
            </ItemsControl.ItemTemplate>
        </ItemsControl>
    </Canvas>
</Window>