'Importance'-based Shadow Map Allocation

Showing per-frame allocation of portions of a single shadow map, based on the 'importance' of each light.

The importance metric is computed as a light's radius of influence divided by its world space distance from the camera. Lights are then sorted into order and assigned a portion of the available shadow map space.

The technique works best when shadow-casting lights are well spread out, causing the 'importance' value to better reflect the amount of shadow map resolution actually required.

The shadow map used here is 2048x2048.

See http://www.john-chapman.net/content.php?id=14 for more info.

Category:

Science & Technology

Tags:

• shadow
• map
• opengl
• glsl
• deferred
• rendering
• c++
• realtime
• graphics
• directx

[ZeroDominance]

Nice idea. I'm planning on doing something like this, except that each part of the shadow map is allocated for an object, so that closer objects take larger shadow maps.

[johnChapman]

@ZeroDominance the shadow map lookup is done from within the lighting stage, so fill rate issues are amortised (rendering the light volume, rather than a full-screen quad).

[ZeroDominance]

@johnChapman I actually got a crude implementation of my idea working, but see already bottlenecks on rendering screen quads. Did you render a screen-space quad for each projected shadow map, or are the shadow maps batched? I'll look into TSM. I've been experimenting with some shadow mapping techniques. Parallel split shadow maps did not look as good for me.

[johnChapman]

@ZeroDominance the shadow map lookup might get complicated; have you looked into trapezoidal shadow maps? They could be combined nicely with a light-ordering technique like this one.

[Pthalicus]

This is also brilliant. I hope you'll upload some more videos demonstrating your work.