# Re: need help with normals

From:
Daniel Pitts <newsgroup.spamfilter@virtualinfinity.net>
Newsgroups:
comp.lang.java.programmer
Date:
Wed, 24 Jun 2009 12:15:17 -0700
Message-ID:
Thorsten Kiefer wrote:

Hi,
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);
}
stripStart += stripCounts[i];
}

for (int i = 0; i < normals.length; ++i) {
normals[i].normalize();
}

return normals;
}

Best Wishes
Thorsten

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)

--
Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/>

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