I’ve been playing around with shadows in VTK as of lately. I may be wrong, but I’m pretty sure they have issues. Here’s a slightly modified example from the VTK examples. Reduced to one light directly above the sphere.
Shadows.cxx (4.8 KB)
You’ll see despite a light being positioned directly above the sphere it produces an ellipse shadow, no matter the view angle. Even worse if you swap lines 143-149 with 153-158. (Or attach a timer and post modified on the light). You’ll find the ellipse shadow varies with the aspect ratio of the window.
I’ve also toyed with the light a great deal (with varying spotlights, point lights, directional lights) all producing the same issues.