SL4.圆角Canvas

            <Canvas Background="Yellow"  Height="195" Name="canvas1" Width="457">
                <Border BorderThickness="30" BorderBrush="Green" Canvas.Left="20"
                        Canvas.Top="40" CornerRadius="30">
              
                </Border>
           </Canvas>

　　Canvas本身没有圆角，需要通过内嵌一个Border边框来实现圆角效果