用VB实现ARGB，方法很简单。
背景R * (1 - A / 255) + 图像R * (A / 255)
背景G * (1 - A / 255) + 图像G * (A / 255)
背景B * (1 - A / 255) + 图像B * (A / 255)
虽然对于图像的处理较为慢一些...(Using VB to implement ARGB, the method is very simple.
Background R * (1 - A / 255) + image R * (A / 255)
Background G * (1 - A / 255) + image G * (A / 255)
Background B * (1 - A / 255) + image B * (A / 255)
Although the image processing is more slow...)