Shadow cost and LOD

BobTheFish · Post by **BobTheFish** » Mon Oct 13, 2008 6:26 am

How expensive in terms of performance are Irrlicht's stencil shadows? Is cost per-polygon, per-light or what?

Does Irrlicht have dynamic mesh LOD generation?

I'm making a game which involves large numbers of models at far distance but very few at close distance. I'd like them to be shadowed in either case, detailed up close and very low polygon/texture detail far away (to increase performance).

Halifax · Post by **Halifax** » Mon Oct 13, 2008 7:04 am

The stencil shadows in Irrlicht are very expensive, and increase in expensiveness with the number of polygons. I recommend that you check out BlindSide's XEffects project which implements shadow mapping.

No, Irrlicht doesn't currently have dynamic LOD mesh generation. I can recommend edge elimination as something you should look into for LOD mesh generation though. It works pretty well, and is very simple to implement.

Basically, for edge elimination, you do dot products on the triangle normals. You then compare the dot product against a tolerance value. If it is lower than the value, you reduce the two triangles, but if it is above, then you keep the triangles.

So edge elimination can be used to reduce polygons, while still preserving the general likeness, or it can be used (with a high tolerance value) for an aggressive LOD approach for when the mesh is a little bit further from the camera.

I hope that helps.

BobTheFish · Post by **BobTheFish** » Mon Oct 13, 2008 12:26 pm

Halifax wrote:you reduce the two triangles

How? I'm not sure what this means.

I hope that helps.

Thanks, it does.

Halifax · Post by **Halifax** » Mon Oct 13, 2008 5:10 pm

BobTheFish wrote:
Halifax wrote:you reduce the two triangles
How? I'm not sure what this means.

You collapse the edge, by taking the first endpoint to the second or vice versa.

To be honest, I don't know why I haven't taken a stab at edge collapsing for Irrlicht. I think I'll give it a try.