Computing normals...

Take the cross (vector) product of two vectors in your plane, then normalise it to get the plane normal.

nx = y1.z2 - z1.y2
ny = z1.x2 - x1.z2
nz = x1.y2 - y1.x2

Then divide each of nx,ny,nz by sqrt(nx^2 + ny^2 + nz^2)

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Sorry for not having explained myself better
i know how to calculate the cross product,
but how should i build my vectors from my vertex list?
(i''d like to have per-vertex normals)

Say you want the normal of a triangle. You know all three points on the triange.

Points are A,B and C (clockwise)

Vector1 (x1,y1,z1) is C-B
Vector2 (x2,y2,z2) is A-B

Calculate all the normals for each polygon, then the normal for a vertex is the average of all the normals of the polygons connected to that vertex.

We do about the same thing, but we keep track of the vertex normal for all three vertices of a face. This allows us to use smoothing groups, where two connected faces will shade quite differently, if they do not belong to the same smoothing group. i.e. two faces have a common vertex, but do not have the same vertex normal for that vertex.

I seem to recall a discussion some time ago on vertex normals. Didn't that discussion bring into the average of the vertex normals the different sizes of the faces?

Edited by - Antknei on December 1, 2000 11:03:11 AM

Thanks guys, my models look much better now
Since i''m only at the begining of my loader, i''ll use one normal per vertex. but keeping somewhere normals for vertex for each face might be useful in a near future...
Thx
Ramses