Sorry - just answering my own post with another observation - in my example, I wondered why the outer right hand wall wasn't blue since the blue light was nearest to it.I'm aware that the walls we're looking at are the back faces of the cube and I'm using two-sided lighting, but if you imagine the coordinates of the lights were inverted, the results would be correct. The blue light would be on the left, the green light in the bottom right corner, etc.Back surfaces don't seem to be lit correctly - I'm inclined to think this is close to the issue George is observing?
Lighting is completely separate from shadows -- shadows require knowledge of the geometry between the light and the shadowed surface (a very complicated problem), while Lighting only requires knowledge of the lightsource and the object being lit (simple).
(again, I'm not on Snow Leopard at the moment, so I'm flying blind here)When a polygon is lit in standard OpenGL lighting, it's per-vertex. This means the light value is calculated at the corners of the polygon, and interpolated across the face of the polygon. This is cheap and easy, and also wrong (if the light's near the center of the face, it doesn't highlight as it ought to, since the center of the face is interpolated from the corners, which would be darker).
With GLSL, it's possible to do per-pixel lighting, which resolves that issue nicely. However, you have to write your shader yourself to get that up and running. (there are examples out there that do this for you already)
Next up, there's 1-sided vs. 2-sided lighting. By default, QC's lighting is 1-sided. That is, it lights the front side (normal-points- towards-the-light case), but not the back side. There's a checkbox in the lighting patch's parameters to enable 2-sided lighting. This will cause the light to work on the back side (normal-facing-away-from-the- light case). You may want to experiment with this setting, to see if it helps. I have a feeling you may be experiencing a combination of both of these issues (per-vertex instead of per-pixel lighting, and 1- sided instead of 2-sided).
Note that when you're culling polygons (face culling), front/back facing is determined by vertex winding (clockwise/counter-clockwise), not normal direction(towards/away). This normally doesn't matter to anyone, as normals aren't exposed much in QC, but if you're writing your own GL code for a plugin you may want to keep that in mind.
-- [ christopher wright ] [email protected] http://kineme.net/
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