View Full Version : Faces stored in arrays

08-22-2000, 09:23 AM
My program loads a dxf file and save each FACE3D in an aray in the following order x,y,z,x,y,z,x... These render perfectly but I'm wonder how do I generate normals or texture objects drawn in this fashion.

08-22-2000, 08:05 PM
I don't know about texture objects, but calculating a normal from a triangle can be done using the cross product. This is the code that I use:

// Calculate two vectors for the x-product,
// where tri_verts is an array holding your
// triangle vertices:

v1 = tri_verts[ 0 ] - tri_verts[ 1 ];
v2 = tri_verts[ 2 ] - tri_verts[ 1 ];

// Use the cross product of the two vectors
// to compute the face normal:

normal.x = v1.y * v2.z - v1.z * v2.y;
normal.y = v1.z * v2.x - v1.x * v2.z;
normal.z = v1.x * v2.y - v1.y * v2.x;

// OpenGL expects normals to be normalized:


This is a normal for a single face and is only useful if you are using flat shading. If you want smooth objects you'll have to average the normals at each vertex.

Hope this helps.