Critique my normal calculations, they're backwards but work!

[dirk103]

Hi, I just recently was able to render coherent terrains after quite a long time of trying. I'm not sure why this works but it does, I simply switched the equation around:

instead of: < what every example i've seen says to do
normal = (v1 - v2) * (v2 - v3)



i tried
normal = (v1 * v2) - (v2 * v3)

and it looks good

why is this so? I don't understand this and it baffles me. did the forces of OpenGL come together and i have a working bug, i've been experimenting with light positioning, and it doesn't appear as if the position of my light matches what I feed it. for example. If i set my light position to:
x = 2571.15
y = 6000
z = 3064.18
??? = 45

it appears as if the center of the light source is closer to
x = z = 60

at least that is where the center of my spot_light_cutoff point is in relation to the terrain that i am drawing.

- I am calling glLightfv after a switch to the modelview matrix, and after i translate to my camera position.


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Another question i have is:

    GLfloat poslight[4] = {x, y, z, ??? };
    glLightfv(GL_LIGHT0, GL_POSITION, poslight );

what is the fourth parameter for?
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* Note, this normal list jumps by four because i'm rendering quads

void ModelObject::CalculateNormals()
{
    for(int i=0;i<normal_count;i+=12) {
        float v1_x = vertexes[i+0];
        float v1_y = vertexes[i+1];
        float v1_z = vertexes[i+2];
 
 
        float v2_x = vertexes[i+3];
        float v2_y = vertexes[i+4];
        float v2_z = vertexes[i+5];
 
 
        float v3_x = vertexes[i+6];
        float v3_y = vertexes[i+7];
        float v3_z = vertexes[i+8];
 
 
 
        normals[i+0] =  (v1_x * v2_x) - (v2_x * v3_x);
        normals[i+1] =  (v1_y * v2_y) - (v2_y * v3_y);
        normals[i+2] =  (v1_z * v2_z) - (v2_z * v3_z);
 
 
        normals[i+3] =  (v1_x * v2_x) - (v2_x * v3_x);
        normals[i+4] =  (v1_y * v2_y) - (v2_y * v3_y);
        normals[i+5] =  (v1_z * v2_z) - (v2_z * v3_z);
 
 
        normals[i+6] =  (v1_x * v2_x) - (v2_x * v3_x);
        normals[i+7] =  (v1_y * v2_y) - (v2_y * v3_y);
        normals[i+8] =  (v1_z * v2_z) - (v2_z * v3_z);
 
 
        normals[i+9] =  (v1_x * v2_x) - (v2_x * v3_x);
        normals[i+10] = (v1_y * v2_y) - (v2_y * v3_y);
        normals[i+11] = (v1_z * v2_z) - (v2_z * v3_z);
 
    }
 
 
// I believe i should normalize to unit length here
 
    // Smooth the normals (for heightmap only)
    for(int i=0;i<normal_count;i+=12) {
        float n1_x = normals[i+0];
        float n1_y = normals[i+1];
        float n1_z = normals[i+2];
 
 
        float n2_x = normals[i+3];
        float n2_y = normals[i+4];
        float n2_z = normals[i+5];
 
 
        float n3_x = normals[i+6];
        float n3_y = normals[i+7];
        float n3_z = normals[i+8];
 
 
        float n4_x = normals[i+9];
        float n4_y = normals[i+10];
        float n4_z = normals[i+11];
 
        float n1 = n1_x + n2_x + n3_x + n4_x;
        n1 /= 4;
        normals[i+0] = normals[i+3] = normals[i+6] = normals[i+9] = n1;
 
        float n2 = n1_y + n2_y + n3_y + n4_y;
        n2 /= 4;
        normals[i+1] = normals[i+4] = normals[i+7] = normals[i+10] = n2;
 
        float n3 = n1_z + n2_z + n3_z + n4_z;
        n3 /= 4;
        normals[i+2] = normals[i+5] = normals[i+8] = normals[i+11] = n3;
 
 
 
    }
}

thank you!