Hi, How do I check to see if an (x,y,z) point is within the viewport? Thank ya kindly, Scooter Email Website
"If you try and don''t succeed, destroy all evidence that you tried."

Do a search for frustum culling.

use gluProject on the point and check if x is >= 0 and < viewport[2] and y is >= 0 and y is < viewport[3]. the z part is just for depth testing. You don''t need it.

example code: (Am I nice or what?)

inline bool pointisonscreen(float x, float y, float z)
{
GLdouble modelMatrix[16];
GLdouble projMatrix[16];
GLdouble sx,sy,sz;
GLint viewport[4];

glGetDoublev(GL_MODELVIEW_MATRIX, modelMatrix);
glGetDoublev(GL_PROJECTION_MATRIX, projMatrix);
glGetIntegerv(GL_VIEWPORT, viewport);

gluProject(x,y,z,modelMatrix,projMatrix,viewport,&sx,&sy,&sz);

if(sx >= 0 && sx < viewport[2] && sy >= 0 && sy < viewport[3])
return true;
else
return false;
}

I just threw that together. I can''t say for sure that it will work.