fixing normals in lightwaves

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Joined: 2002.04
Post: #17
I imported your model into Form*Z and I can see what's wrong with it. The six standing cuboids are fine, but the big floor slab is topologically malformed and has 'reversely coincident faces' (as Form*Z describes it).

I'll try to explain what I'm seeing: each face of the floor slab object is a rectangle (apart from the bottom, which doesn't exist). Each rectangle has been divided into two triangles by a diagonal line, and both of those triangles have their normals pointing in the same direction. At the same time, another pair of triangles overlay the same rectangle, dividing it across the other diagonal and with normals pointing in the opposite direction to the first pair. This means that the rectangle is double sided ('reversely coincident'), and if your renderer uses a Z-buffer and draws backfaces you'll randomly see either the front face, the back face, or a bit of both. The back face is probably in shadow, so you'll see an appropriately dark colour.

I was able to fix the problem in Form*Z by deleting the unwanted inward-facing triangles, but you'd probably be better off redrawing the floor polygon and extruding it again instead of trying to fix it!

Neil Carter
Nether - Mac games and comic art
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