3d Theory. vcs to scs transformation.

Question

Hi you 3d gurus.
Please give me a tip!
If you have a point with coordinates given in the View Coordinate System, how do you translate it to a point on the screen?
The point is given by x,y,z in the view coordinate system (vcs). (x is horizontal, y is vertical, and z is distance stright forward from your eye.)
To obtain where to render the point at the screen, I could do something like this:
iScreenX = (400*vcs.x)/vcs.z;
iScreenY = (400*vcs.y)/vcs.z;The problem is that this only works for z values grather than 0.
if(vcs.z <= 0)
IHaveAProblem();
Ofcorse, a point with negative (or zero) z- value shold not be shown, however, a polygon might be visible even though one of its vertexes has a negative z- value. Havent found any good solution. So far, I just dont paint the polygon at all if I find a negative or zero z.
I also tried using the distance, and not the z- value as the divisor:
double dDivisor;
dDivisor = Math.sqrt(vcs.x*vcs.x +vcs.y*vcs.y +vcs.z*vcs.z);
iScreenX = (400*vcs.x) / dDivisor;
iScreenY = (400*vcs.y) / dDivisor;This is ok for all points not beeing positioned in the middle of your eye (givig dDivisor=0), but it gives a fisheye like view of the world, and thats not exactly what I want.
I want something close to the first solution, but that also works on negative and 0 z values.
Anybody knows?
This is my 3d engine:
http://blake.prohosting.com/ragnvald/
Ragnvald Barth
Software engineer

Answer 1

Well, as jsalonen (and I) said in the other forum, it involves some tricky stuff. You can either use clipping (check where the polygons collide with the viewpoint and 'clip' them, creating new polygons that can be drawn) or Z buffering, which produces the best quality but also needs extra memory, the size of the view screen actually. So z buffering sucks memory a lot. Then the easiest way is that you don't draw polygons that are too near you.