How does Vertex-Lit rendering work?

Questions & Answers
1

Hello everyone,
Just a pair of questions about Vertex-Lit rendering…

For my project i would want to have some very large level-wide objects that have to be affected by many realtime lights at the same time in different places. Is vertex-lit rendering someway conservative on the number of lights affecting a single object? Would I face some problems trying to lit a single huge mesh with a tons of lights that have to affect only a little part of the mesh? I have tried testing this but i encountered another problem along the way…

When i duplicate some lights in the scene (always using vertex-lit rendering and vertex-lit shader everywhere) their effect on a particular mesh disappears… this happens more often when the duplicated lights have a short range and when the mesh is affected by other lights with different ranges, colours and intensity. Is this a weird problem I am facing, or some limitation of the vertex-lit rendering path? Can i solve this anyway?

Thanks and sorry for bad english, hope someone understood something…

2

Is there a specific reason to use vertex-lit rendering path? If not, I would suggest deferred rendering path, since it has very little effect on performance as the number of lights increase. In addition deferred rendering is per-pixel lighting.

Even with vertex-lit rendering a huge amount of lights might cause performance issues even though vertex-lit rendering is generally very fast. Vertex-lit rendering might also give undesirable results. For example if there are multiple lights and mesh vertices are rather far, then the lights have very little or no effect at all (compare two images here: GLSL Programming/GLUT/Smooth Specular Highlights - Wikibooks, open books for an open world ).

You could state your case more specifically if this does not answer to your question.