Light leak from Virtual Shadow Maps based on Source Radius

midgunner66 · March 5, 2022, 2:27am

I think this is it; the artifact they mention matches what you’re getting:

Penumbra Artifacts

By default, Virtual Shadow Maps only guarantees that the samples around the ray origin (the receiver pixel) will be present. As the algorithm traverses the ray, it can encounter unmapped pages where no shadow data exists. A variety of techniques are used to reduce the impact of this, including dilating the page mappings slightly and having various fallbacks in place during iteration. Even still, occasional artifacts stemming from missing pages can happen, especially around edges of the screen when zoomed in on soft penumbra. These artifacts will manifest as noisy light leaks in shadowed areas.

Like other limitations with VSMs, issues can mostly be avoided by keeping shadow penumbra sizes reasonable and avoiding zooming in to the point where they cover large portions of the screen.