[osg-users] Issue with shadow

[Pete Black]

Its becase OSG's default shadowMap code isn't very good for large scenes - the shadow camera frustum is sized to fit the entire scene, so an individual shadow map pixel may cover a large number of rendered fragments, making the shadows very pixellated, and the 'shadow acne' - caused by a similar aliasing issue is severe.

the 'Soft shadow map' technique does some filtering which improves things a fair bit, and there are other algos like LISPSM which try to use shadowmap pixels more efficiently.

The 'standard' approach to this in other engines is to use cascaded shadow maps, which render multiple passes and combines them to make close-up and distance shadows work nicely, but this approach is not implemented in osgShadow AFAIK.

heres some info on shadow mapping details:

http://www.opengl-tutorial.org/intermediate-tutorials/tutorial-16-shadow-mapping/

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