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  Pyramids with square bases  (Read 1316 times)
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Offline silverklyph

Senior Newbie




Java games rock!


« Posted 2003-11-28 18:16:51 »

Ok, I'm a noob to the very core of the definition of the word, but pardon the stupidity of my question:

 I've been playing around with Xith3D for all of a week now, and I'm trying to use the the Cube.createCubeViaTriangles() idea to create a pyramid with a square base.  Unfortunately, anytime i call the following method, it returns a simple, 2D triangle:

   public static Geometry createTriangle(float x, float y, float z, float size){
             float half = size/2f;

       Point3f[] coords = new Point3f[] {

           new Point3f(x, y+half, z),
           new Point3f((float)(x+half*Math.cos(Math.PI/6)), y-half, (float)(z+half*Math.cos(Math.PI/2))),
           new Point3f((float)(x-half*Math.cos(Math.PI/6)), y-half, (float)(z+half*Math.cos(Math.PI/2))),

           new Point3f(x, y+half, z),
           new Point3f((float)(x+half*Math.cos(Math.PI/6)), y-half, (float)(z+half*Math.cos(Math.PI/2))),
           new Point3f((float)(x+half*Math.cos(Math.PI/6)), y-half, (float)(z-half*Math.cos(Math.PI/2))),

           new Point3f(x, y+half, z),
           new Point3f((float)(x-half*Math.cos(Math.PI/6)), y-half, (float)(z+half*Math.cos(Math.PI/2))),
           new Point3f((float)(x-half*Math.cos(Math.PI/6)), y-half, (float)(z-half*Math.cos(Math.PI/2))),

           new Point3f(x, y+half, z),
           new Point3f((float)(x-half*Math.cos(Math.PI/6)), y-half, (float)(z-half*Math.cos(Math.PI/2))),
           new Point3f((float)(x+half*Math.cos(Math.PI/6)), y-half, (float)(z-half*Math.cos(Math.PI/2)))
       };

       Color3f[] colors = new Color3f[] {

           new Color3f(1f,1f,1f),
           new Color3f(1f,0f,0f),
           new Color3f(0f,1f,0f),

           new Color3f(0f,1f,0f),
           new Color3f(0f,0f,1f),
           new Color3f(1f,1f,1f),

           new Color3f(1f,1f,1f),
           new Color3f(1f,0f,0f),
           new Color3f(0f,1f,0f),

           new Color3f(0f,1f,0f),
           new Color3f(0f,0f,1f),
           new Color3f(1f,1f,1f),
       };

       TriangleArray qa = new TriangleArray(coords.length, GeometryArray.COORDINATES|GeometryArray.COLOR_3|GeometryArray.TEXTURE_COORDINATE_2);

       qa.setCoordinates(0,coords);
       qa.setColors(0,colors);

       return qa;
 }


What am I doing wrong?
Offline Jeff

JGO Coder




Got any cats?


« Reply #1 - Posted 2003-11-29 01:57:32 »

Well, without going any deeper into it, I only see 4 vertexes.

A square based pyramid has 5.  The 4 base corners and the top.


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Offline cfmdobbie

Senior Devvie


Medals: 1


Who, me?


« Reply #2 - Posted 2003-11-29 08:36:04 »

You've got four sides defined by three points each.  Scanning down the signs on your list of vertices, I see two z-components with +,-.  I expect one of those should be -,+.  When you say you're only seeing one triangle, I take it you can't see any others from any other angle?  Even below?

I'll guess the winding order of your vertices is wrong, so you're only seeing the back of the faces, which are being culled - apart from the one triangle that is the other (correct) way around.  Try the following instead:

1  
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new Point3f(x, y+half, z),
new Point3f((float)(x-half*Math.cos(Math.PI/6)), y-half, (float)(z+half*Math.cos(Math.PI/2))),
new Point3f((float)(x+half*Math.cos(Math.PI/6)), y-half, (float)(z+half*Math.cos(Math.PI/2))),
 
new Point3f(x, y+half, z),
new Point3f((float)(x+half*Math.cos(Math.PI/6)), y-half, (float)(z+half*Math.cos(Math.PI/2))),
new Point3f((float)(x+half*Math.cos(Math.PI/6)), y-half, (float)(z-half*Math.cos(Math.PI/2))),
 
new Point3f(x, y+half, z),
new Point3f((float)(x-half*Math.cos(Math.PI/6)), y-half, (float)(z-half*Math.cos(Math.PI/2))),
new Point3f((float)(x-half*Math.cos(Math.PI/6)), y-half, (float)(z+half*Math.cos(Math.PI/2))),
 
new Point3f(x, y+half, z),
new Point3f((float)(x+half*Math.cos(Math.PI/6)), y-half, (float)(z-half*Math.cos(Math.PI/2))),
new Point3f((float)(x-half*Math.cos(Math.PI/6)), y-half, (float)(z-half*Math.cos(Math.PI/2)))

Hellomynameis Charlie Dobbie.
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Offline silverklyph

Senior Newbie




Java games rock!


« Reply #3 - Posted 2003-11-29 09:23:56 »

AAAAHHH!!! My trig was off.  I was using the cos(pi/2) instead of the cos(pi/4).  

Cos(pi/2) == 0

That's where I was going wrong... thanks for reposting the code so I could look through it more carefully!
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