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Index › Programming Questions & Help › Programs › Trig for a star..

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Trig for a star.. (Read 1344 times)

chrism1th YaBB Newbies Offline Posts: 7 IL	Trig for a star.. Mar 29^th, 2009, 6:31pm Trying to create a star with processing.. any ideas why it sometimes doesn't complete the circumference http://www.openprocessing.org/visuals/?visualID=1324 I don't see the problem

Cedric

Re: Trig for a star..
Reply #1 - Mar 29^th, 2009, 7:38pm

Alright, took me a while but I needed to know.

That problem was that "a" was rounded after multiplying it so everytime it was a decimal number it was rounded so when you then mutiplied it by "n" you didnt fill up a total 360 degrees and got that gap. You didnt get it everytime cause, when it wasnt a decimal it worked fine.

I changed it by making your i a float. Maybe there are better ways to do it. but worked fine...

just change that part

private void calcPoly(){
Point p;
float i=0, n = points.length;
float a = 360/n;
float cosa, sina;

for( i=0;i<n;i++){

points[int(i)] = new Point(0,0);
p = points[int(i)];
cosa = cos((a*i) * PI/180);
sina = sin((a*i) * PI/180);
if(i%2==0){
p.x = r1 * cosa;
p.y = r1 * sina;
}else{
p.x = r2 * cosa;
p.y = r2 * sina;
}

}
}

twitter.com/CedricKiefer

chrism1th

Re: Trig for a star..
Reply #2 - Mar 30^th, 2009, 9:18am

Thanks for the digging!! You were right about changing the int to a float, but it wasn't the i that was affecting the outcome, it was the n;

Because a comes from 360/n. I didn't realize that an integer would take precedence in a calculation in Java.

Code:


     int i=0;
     float n = points.length; 
     float a = 360/n; 
     float cosa, sina; 
      
     for(i=0;i<int(n);i++){ 
       points[i] = new Point(0,0); 
        p = points[i]; 
        cosa = cos((a*i) * PI/180); 
        sina = sin((a*i) * PI/180); 
        if(i%2==0){ 
           p.x = r1 * cosa; 
           p.y = r1 * sina; 
        }else{ 
           p.x = r2 * cosa; 
           p.y = r2 * sina; 
        }          
     }

Cheers!

Cedric YaBB Moderator Offline Posts: 1838	Re: Trig for a star.. Reply #3 - Mar 30^th, 2009, 9:52am true.... my fault... was late last night anyway, case solved!
	twitter.com/CedricKiefer

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