Screen space indirect lighting with visibility bitmask

Horizon-based indirect illumination efficiently estimates a diffuse light bounce in screen space by analytically integrating the horizon angle difference between samples along given direction. Like other horizon-based methods, this technique cannot properly simulate passing behind thin surfaces. We propose concept of visibility bitmask that replaces two angles bit field representing binary state (occluded/un-occluded) N sectors uniformly distributed around hemisphere slice. It allows to pass surfaces constant thickness while keeping efficiency methods. can also do more accurate ambient lighting than bent normal sampling one cone. This improves visual quality occlusion, diffuse, and compared previous methods minimizing noise low performance overhead.