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Normal Vector and winding

Started by stevenie Jun 16, 2010 at 12:45 AM 0 replies 800+ views

Original Post

Jun 16, 2010 at 12:45 AM

Hi everyone,

I'm learning lighting from NeHe. In the example. the author uses normal vectors to tell opengl which face is "up".

I'm wondering why not use winding instead of normal vector? If I have some complex objects, do I need to give a normal vector for every triangle? Thanks!

Steven

Hodgman

Jun 16, 2010 at 12:52 AM

Normals are supplied per-vertex, wheras front/back facing is determined per-triangle (from the winding order).

It's possible/valid to have a triangle facing up, where two of it's vertices have normals pointing up and one has a normal pointing down.

Usually, all the normals on a triangle won't be facing in the exact same direction -- if they were, then the lighting would have jagged edges (see Flat vs smooth shading)

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