For our first simple effect, we will draw an alpha-blended (semitransparent) circle at a fixed position over the video stream. The first step is to add the drawing functions to the screen.c.
对于第一个简单效果，将在视频流中的固定位置绘制一个阿尔法混合(半透明的)圆。
2
Video card or driver doesn't support separate alpha blend, glow will be disabled.
显卡或驱动不支持分离的透明度混合渲染，显示功能将被禁用。
3
Fixed issue with distorted video when converting it in alpha matte.