渐变画刷示例

        <Rectangle>
            <Rectangle.Fill>
                <LinearGradientBrush>
                    <LinearGradientBrush.StartPoint>
                        <Point X="0" Y="0" />
                    </LinearGradientBrush.StartPoint>
                    <LinearGradientBrush.EndPoint>
                        <Point X="1" Y="1" />
                    </LinearGradientBrush.EndPoint>
                    <LinearGradientBrush.GradientStops>
                        <GradientStopCollection>
                            <GradientStop Color="Yellow" Offset="0.0" />
                            <GradientStop Color="Red" Offset="0.25" />
                            <GradientStop Color="Blue" Offset="0.75" />
                            <GradientStop Color="LimeGreen" Offset="1.0" />
                        </GradientStopCollection>
                    </LinearGradientBrush.GradientStops>
                </LinearGradientBrush>
            </Rectangle.Fill>
        </Rectangle>

        <Rectangle>
            <Rectangle.Fill>
                <LinearGradientBrush>
                    <LinearGradientBrush.StartPoint>
                        <Point X="0" Y="0" />
                    </LinearGradientBrush.StartPoint>
                    <LinearGradientBrush.EndPoint>
                        <Point X="1" Y="1" />
                    </LinearGradientBrush.EndPoint>
                    <LinearGradientBrush.GradientStops>
                        <GradientStopCollection>
                            <GradientStop Color="Yellow" Offset="0.0" />
                            <GradientStop Color="Red" Offset="0.25" />
                            <GradientStop Color="Blue" Offset="0.75" />
                            <GradientStop Color="LimeGreen" Offset="1.0" />
                        </GradientStopCollection>
                    </LinearGradientBrush.GradientStops>
                </LinearGradientBrush>
            </Rectangle.Fill>
        </Rectangle>

LinearGradientBrush.StartPoint：表示渐变方向的起始点，默认是坐标为0，0的点

LinearGradientBrush.EndPoint：表示渐变方向的结束点，默认是坐标为1，1的点，与StartPoint结合起来表示渐变的方向

LinearGradientBrush.GradientStops：GradientStop的集合，描述渐变中过渡点的位置和颜色