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playworker
09-11-2002, 08:45 AM
Sorry in advance for asking something that has probably been asked many times before.

I can't seem to get the code right for generating normals from vertex info...

Please could somebody post a snippet of code for generating vertex normals.

Thanks

Matt

coredump
09-11-2002, 08:58 AM
ok. let's say a triangle is composed of vertices v0, v1 and v2 in a counter-clockwise order. make 2 vectors: vec1 = (v1 - v0) and vec2 = (v2 - v0). now take the cross product: vec1 X vec2. normalize the resultant vector (divide each component by the vector's length) and you have your normal!

b

[This message has been edited by coredump (edited 09-11-2002).]

pleopard
09-11-2002, 09:08 AM
/*_FILE:norm.c
*--------------------------------------------------------------
*
* Module Name : facet3norm
*
* Purpose :
* compute a unit vector normal to a
* three sided facet
*
*
*-------------------------------------------------------------*/
void norm(vertices,normal)
float vertices[4][3];
float normal[3];
{
float s0[3],s1[3];
float n0[3],n1[3];
float m0;
register short i;

/* get two side vectors */

for (i=0; i<=2; i++)
{
s0[i] = vertices[0][i] - vertices[3][i];
s1[i] = vertices[1][i] - vertices[0][i];
}

/* compute surface normal by crossing s0 with s1 */

cross(n0,s0,s1);

/* compute magnitude of normal */

m0 = magnitude(n0);

/* normalize to unity and copy to returned array */

for (i=0; i<=2; i++)
{
normal[i] = n0[i]/m0;
}
}