Let’s create a light weighted wpf drop shadow effect, considering that the origin one performs badly in some special occasions.
As I mentioned before (check it out), the original WPF DropShadow Effect can cause severe preformance problem. Due to the “flaw” M$FT brought to the HLSL support for WPF, the Effect class that implements the visual effect creates and destroy GPU resource each frame, which is the worst thing you could do with GPU resources. So, what about implementing a custom shadow effect to avoid it? This sounds interesting.

– 春节补充

高斯模糊（ https://zh.wikipedia.org/wiki/%E9%AB%98%E6%96%AF%E6%A8%A1%E7%B3%8A ）是一种常见的图像处理算法，使用高斯分布与图像做卷积，得到模糊的效果。其二维定义：

σ是正态分布的标准偏差。在应用的时候，假设σ为2.5。对于模糊半径为1，则高斯矩阵为3*3的一个矩阵，以[1,1]为中心，带入公式计算高斯矩阵的值，得到：