need help with normals

[Thorsten Kiefer]

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 = new Vector3f();
}
Vector3f[] coordVs = new Vector3f[coords.length];
for (int i = 0; i < coordVs.length; ++i) {
coordVs = new Vector3f(coords);
}

int stripStart = 0;
for (int i = 0; i < stripCounts.length; ++i) {
Vector3f x0 = coordVs[coordIndices[stripStart]];
for (int j = 2; j < stripCounts; ++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]].add(cp);
normals[coordIndices[stripStart + j]].add(cp);
normals[coordIndices[stripStart + j - 1]].add(cp);
}
stripStart += stripCounts;
}

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

return normals;
}


Best Wishes
Thorsten

 

[Daniel Pitts]

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 = new Vector3f();
}
Vector3f[] coordVs = new Vector3f[coords.length];
for (int i = 0; i < coordVs.length; ++i) {
coordVs = new Vector3f(coords);
}

int stripStart = 0;
for (int i = 0; i < stripCounts.length; ++i) {
Vector3f x0 = coordVs[coordIndices[stripStart]];
for (int j = 2; j < stripCounts; ++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]].add(cp);
normals[coordIndices[stripStart + j]].add(cp);
normals[coordIndices[stripStart + j - 1]].add(cp);
}
stripStart += stripCounts;
}

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

 

[John B. Matthews]

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, EPSILON);
}
}
}
</code>

 

[Thorsten Kiefer]

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, 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

 

[Thorsten Kiefer]

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, 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

 

[John B. Matthews]

[...]

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).

Sorry, I have no knowledge of IndexedTriangleFanStrip, but I was curious
about rendering a mesh of trigons in 3D using Java. I'd be grateful for
any links.

The last tool I used for this had a convenient feature that calculated
the normal vector on the fly. It assumed a consistent ordering of the
vertices: left-handed v. right-handed. The trick was finding the few odd
triangles that had gotten flipped at the source.