Re: need help with normals

Daniel Pitts <>
Wed, 24 Jun 2009 12:15:17 -0700
Thorsten Kiefer wrote:

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

    public static Vector3f[] computeNormals(Point3f[] coords, int[]
coordIndices, int[] stripCounts) {
        Vector3f[] normals = new Vector3f[coords.length];
        for (int i = 0; i < normals.length; ++i) {
            normals[i] = new Vector3f();
        Vector3f[] coordVs = new Vector3f[coords.length];
        for (int i = 0; i < coordVs.length; ++i) {
            coordVs[i] = new Vector3f(coords[i]);

        int stripStart = 0;
        for (int i = 0; i < stripCounts.length; ++i) {
            Vector3f x0 = coordVs[coordIndices[stripStart]];
            for (int j = 2; j < stripCounts[i]; ++j) {
                Vector3f x1 = coordVs[coordIndices[stripStart + j]];
                Vector3f x2 = coordVs[coordIndices[stripStart + j - 1]];
                Vector3f d1 = new Vector3f();
                Vector3f d2 = new Vector3f();
                Vector3f cp = new Vector3f();
                d1.sub(x1, x0);
                d2.sub(x2, x0);
                cp.cross(d1, d2);
                normals[coordIndices[stripStart + j]].add(cp);
                normals[coordIndices[stripStart + j - 1]].add(cp);
            stripStart += stripCounts[i];

        for (int i = 0; i < normals.length; ++i) {

        return normals;

Best Wishes

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"

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