## 3D Help

Ok, so a while back I decided to challenge myself to create a working 3D engine without looking at any tutorials. I've got what I think is a pretty good prototype, but the z-axis is giving me some really odd behavior.

Here's my code (also, this is in AS2):

PHP Code:
``` var magic = 180/Math.PI; function getA(x1,y1,z1,x2,y2,z2) {     var d = Math.sqrt((x2-x1)*(x2-x1)+(z2-z1)*(z2-z1));     var yd = y2-y1;     var r = Math.atan2(yd,d)*magic;     return r; } function aDist(a1,a2) {     var a = a2-a1;     if (a > 180) a -= 360;     else if (a < -180) a += 360;     return a; } p0 = [0,0,0]; p1 = [0,100,0]; p2 = [0,0,100]; p3 = [0,100,100]; p4 = [100,0,0]; p5 = [100,100,0]; p6 = [100,0,100]; p7 = [100,100,100]; p8 = [50,50,50]; var x = 50; var y = 50; var z = -50; var xa = 0; var ya = 0; onEnterFrame = function() {     removeMovieClip(s);     createEmptyMovieClip("s",1);          if (Key.isDown(Key.UP)) z++;     if (Key.isDown(Key.DOWN)) z--;     if (Key.isDown(Key.LEFT)) x++;     if (Key.isDown(Key.RIGHT)) x--;          if (xa >= 360) xa = 0;     else if (xa < 0) xa = 359;     for (var n=0; _root["p"+n]; n++) {         p = _root["p"+n];         s.attachMovie("a","a"+n,n);         o = s["a"+n];                  x2 = getA(y,x,z,p,p,p);         y2 = getA(x,y,z,p,p,p);         //x2 = aDist(x2,xa);         //y2 = aDist(y2,ya);                  o._x = x2;         o._y = y2;     } }  ```
My problem is that whenever the z position gets within the box's depths, even when the camera is outside the box, the box seems to invert itself.

To explain my methodology a bit, I'm rendering any given object (or, as of now, point) by finding it's x&y angles relative to the position of the camera and then just using that angle as a strait up x/y position. There is no view limit right now, affording the player a 360 degree view around themselves.

In theory, this would mean that an x/y/z position of 50/50/-50 would render this box the same as -50/50/50. Yet while 50/50/-50 seems to render the box just fine, -50/50/50 renders it in a triangular shape.

I really can't wrap my head around why this would be happening, any ideas?