I am using the following C routine, adapted from the openGL wiki, to calculate surface normals:

```
void setnormal (vect P1, vect P2, vect P3) { /* from openGL wiki pseudo-code */
vect U,V;
/* Set Vector U to (Triangle.p2 minus Triangle.p1)
Set Vector V to (Triangle.p3 minus Triangle.p1)
Set Normal.x to (multiply U.y by V.z) minus (multiply U.z by V.y)
Set Normal.y to (multiply U.z by V.x) minus (multiply U.x by V.z)
Set Normal.z to (multiply U.x by V.y) minus (multiply U.y by V.x) */
vectminus(P2,P1,U);
vectminus(P3,P1,V);
normal[0]=(U[1]*V[2])-(U[2]*V[1]);
normal[1]=(U[2]*V[0])-(U[0]*V[2]);
normal[2]=(U[0]*V[1])-(U[1]*V[0]);
}
```

vectminus() just does the simple arithmetic. “normal” is a global float[3]. There is no scaling in the scene. The routine gets called this way:

```
setnormal(one,three,two); glNormal3fv(normal);
```

Two and three are reversed because the vectors are usually also being used as the corners of some polygon, and this seems to be the best arrangement. I have a scene where I can move both the camera and the single light, and the normals seem fine except the intensity of the light is out of proportion.

Here the light is about 85 degrees from vertical in relation to the origin, where the pyramid is (ie. it is about to “set”). But these are the colors and light intesity:

```
float darkorangered[3]={0.5f,0.1f,0.0f};
float ambient[4]={0.1f,0.1f,0.1f,1.0f};
float diffuse[4]={0.1f,0.1f,0.1f,1.0f};
```

So viewed without GL_LIGHTING,

Obviously, when facing the light the color values of the pyramid are being multiplied to excess, which also seems strange considering the very low intensity of the light. I presume this has something to do with the normals?

If anyone has a clue that would be great. Here’s the setup routine for the lighting:

```
void init(float R, float G, float B) {
// glEnable(GL_CULL_FACE);
glEnable(GL_DEPTH_TEST);
glClearColor(R,G,B,1.0f);
if (LIT) {
glEnable(GL_LIGHTING);
glEnable(GL_COLOR_MATERIAL);
glColorMaterial(GL_FRONT,GL_AMBIENT_AND_DIFFUSE);
glLightfv(GL_LIGHT0,GL_AMBIENT,ambient);
glLightfv(GL_LIGHT0,GL_DIFFUSE,diffuse);
glEnable(GL_LIGHT0);
arrangelamp(0.0f);
}
}
```

arrangelamp() just involves the light coordinates.