Re: need help with normals

From:

Thorsten Kiefer <cylinder@news.cnntp.org>

Newsgroups:

comp.lang.java.programmer

Date:

Thu, 25 Jun 2009 16:23:19 +0200

Message-ID:

<4a438857$0$29137$6e1ede2f@read.cnntp.org>

Thorsten Kiefer wrote:

John B. Matthews wrote:

In article <cXu0m.36322$Ig.15935@newsfe14.iad>,
Daniel Pitts <newsgroup.spamfilter@virtualinfinity.net> 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:

<http://jscience.org/api/index.html>

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

public class VectorCrossTest {

    private static final double EPSILON = 1e-15;

    @Test
    public void testMain() {
        System.out.println("testing...");
        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) {
        System.out.println(v);
        for (int i = 0 ; i < v.getDimension(); i++ ) {
            Assert.assertEquals(v.getValue(i), values[i], EPSILON);
        }
    }
}
</code>

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 ???

tk

Hi,
One can have arbitrarily many normals. It's just important to
connect the right normal to the right vertex index. In deed I use
smooth normals, so I just compute as many normals as there are
vertices. My first mistake was that I didn't normalize the
cross product before adding, which lead to useless normal
weighting (do you know what i mean ?). My second mistake
was that I didn't connect the right vertex index to the right
normal index. I fixed this, and now it works fine.
Are you interested in a X3D loader for Java, which supports http ?
I wrote a pretty primitive one (no textures supported).

Regards
Thorsten