Re: need help with normals

Thorsten Kiefer <>
Thu, 25 Jun 2009 14:44:28 +0200
John B. Matthews wrote:

In article <cXu0m.36322$Ig.15935@newsfe14.iad>,
 Daniel Pitts <> wrote:

Thorsten Kiefer wrote:

I wrote normal calculator for IndexTriangleFanStrip, but it calculates
partially wrong normals, can anyone help me with that ?


Please provide an SSCCE. Actually, it would be even better in this
case to provide a Unit Test, complete with assertEqual statements
that show what values you are expecting, but not getting.

Either way, it must be stand-alone compilable and easily runnable (I
consider JUnit tests to be easily runnable, as well as standard
"main" methods)

I'd be interested, too. Here's an example using the JScience library:


import junit.framework.Assert;
import org.jscience.mathematics.vector.Float64Vector;
import org.junit.Test;

public class VectorCrossTest {

    private static final double EPSILON = 1e-15;

    public void testMain() {
        Float64Vector v1 = Float64Vector.valueOf(1, 0, 0);
        Float64Vector v2 = Float64Vector.valueOf(0, 1, 0);
        check(v1.cross(v2), 0, 0, 1);
        check(v2.cross(v1), 0, 0, -1);
        check(v1.cross(v2).cross(v1), 0, 1, 0);

    private void check (Float64Vector v, double... values) {
        for (int i = 0 ; i < v.getDimension(); i++ ) {
            Assert.assertEquals(v.getValue(i), values[i], EPSILON);

OK I think i found the problem, I'm confused.
In an IndexedTriangleFanStrip are the normals supplied per Vertex
or per Index ? e.g a cube has 8 Vertices, but 24 indices with 4 indices per
Triangle Fan -> 6 Fans (6 polys).
Now do I have to compute 8 Normals or 24 ???


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