Shadow Map–Friendly Geometry
Creating geometry that works well in shadow maps allows for more flexibility when combating artifacts like Peter Panning and shadow acne.
Hard edges are problematic for self-shadowing. The depth disparity near the tip of the edge is very small. Even a small offset can cause objects to lose their shadows.
Sharp edges cause artifacts stemming from low-depth disparity with offsets
Narrow objects such as walls should have backs even if they are never visible. This will increase the depth disparity.
It's also important to make sure that the direction the geometry is facing is correct; that is, the outside of an object should be back facing and the inside of an object should be front facing. This is important for rendering with back-face culling enabled, as well as for combating the effects of depth bias.
AFAIK, that's why we have shadows cast from backfaces to combat Peter Panning and shadow acne, the so-called Carmack's reverse.
Edited by Judith, 06 October 2018 - 10:45 AM.