【Half Lambert】
Half Lambert was a technique created by Valve as a way of getting the lighting to show the surface of an object in low-light areas. It basically brightens up the diffuse lighting of the Material and wraps the diffuse light around an object's surface.
Half Lambert用于在低光照环境下让物体显得更亮的算法。该算法提高了diffuse的亮度。
可以看到，和普通的Lambert相比，difLight不再clamp到0-1，而是保持(-1)-1，然后乘以0.5+0.5转换到0-1区间。
通过这种转换，加强了法线的点积值，即加强的光照。
The following shows the diffuse value mapped to a function graph, showing the result of the Half Lambert calculation:
