Remaining shadow issues

[spiralhalo]

• Entities don't cast shadow is they are in camera occlusion-culled region.
• Esp. underground: shadow holes caused by the objects that casts shadow being outside the light frustum's near clipping plane.
• Esp. underground, during sunrise and sunset: shadow holes caused by back-face culling.
• Extra: being able to limit shadow render distance reliably can help alleviate the cost of rendering more shadows to solve above issues.

[spiralhalo]

Entities don't cast shadow if they are in camera occlusion-culled region.

Correction: Entities don't cast shadow if they are outside of camera frustum most likely. Terrain iterator seem to already have a routine to set shadow-visible region to "entities visible", so likely not occlusion issue.

Potential solution is to perform a second "should render" check using a shadow-aware frustum during entity rendering, and if passing despite failing the first check, render the entity as shadow extras only.