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curveVertex problem (Read 1017 times)
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curveVertex problem
Jan 7th, 2006, 9:05pm  
OK, I'm quite a newbie here but heck, I thought I should be able to build a simple 3D poly-curve.  But I apparently don't know how to use curveVertex in 3D correctly.

This program draws a box and two planar polygons.  To the right initially you see a triangle, and I was hoping to have to the left a half-circle.  Nothing shows up there.  If I replace the curveVertex calls with simple vertex calls, I get a triangle to the left.  So the code is not completely nuts!

Am I using the curveVertex primitive incorrectly?  Or is there a problem with it in 3D?

Thanks!!

Owen

import processing.opengl.*;

void setup() {
 size(512, 512, OPENGL); // OPENGL or P3D
 framerate(15);
 drawScene(0,0);
}
void draw() {
 if (mousePressed) {
   drawScene((mouseY - height/2)*.01,(mouseX - width/2)*.01);
 }
}

void drawScene(float xrot, float yrot) {
 background(128);
 translate(width/2, height/2);
 scale (width/4, width/4, width/4);
 rotateX(xrot);
 rotateY(yrot);
 
 box(.5);

 beginShape(POLYGON);
 vertex(0, 1, 0);
 vertex(1, 0, 0);
 vertex(0, -1, 0);
 endShape();

 beginShape(POLYGON);
 curveVertex(0, 1, 0);
 curveVertex(-1, 0, 0);
 curveVertex(0, -1, 0);
 endShape();
}
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Ira
Re: curveVertex problem
Reply #1 - Jan 9th, 2006, 7:57pm  
curve/curveVertex generates a spline curve, based on a  catmull-rom implementation. This just means that each a point on the curve is determined by 2 control points, one that comes before and one that comes after it. In your sketch only your middle vertex has control points on either side. Since you're generating a closed a form, I just reused the ending and starting points, which allowed your curve to go through all your points, which is another characteristic of catmull-rom curves.
Also, You can specify the tightness of the curve with curveTightness().
Code:

  curveTightness(-.25);
  beginShape(POLYGON);
  curveVertex(0, -1, 0);
  curveVertex(0, 1, 0);
  curveVertex(-1, 0, 0);
  curveVertex(0, -1, 0);
  curveVertex(0, 1, 0);
  endShape();


I hope this helps.
ira
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backspaces
Re: curveVertex problem
Reply #2 - Jan 12th, 2006, 7:28pm  
Wow, thanks!

Owen
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