What I'm trying to find - On a normal X, Y coordinate plane, I'm trying to find a formula or group of formulas to find at which point two polygons overlap. The main problem with this is that this includes irregular polygons of any varying amount of sides. All I really know are the points and their order.

Why - I'm trying to implement color into a 3d true basic program. For anyone who hasn't worked with true basic, it doesn't understand depth. (I'll point out at this point that I know there's a download to add that to it, but I'm trying to see if I can do this anyway. Besides, I don't think my school is going to let me install the extras for that.) All and all, I've got wire frame support set up, and it works fairly well. But since it doesn't know depth, if I were to add color to it, I'd need a way to order what I'm drawing. Otherwise, something in back of something else could be drawn on top of it. So, I figure that I could check each group of polygons to figure out if they're overlapping. If they are, the I just pick a point that they have in common, find the placement on the z-axis, and it's all fairly simple from there. (Side Note: The z-axis is something that I have it change in the background, but it doesn't know what to do with it plot-wise)

So there's my problem. I'm not sure if this is really college level math, but I'm guessing it is. I'm in high school right now, and I've yet to find a teacher who knows how to do this.

Thanks for the help.

PS - If you have True basic, and would like to see the programs, I could send them to you. But they're a bit of a mess right now. (haven't cleaned them up code-wise)