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Index › Programming Questions & Help › Programs › matrix scale
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matrix scale (Read 988 times)
ukicar
matrix scale
Dec 1st, 2006, 5:16pm  
Hello,

Maybe this problem has something with precision conversion but I'm not sure. I'm using keys UP and Down to increase matrix size but after some greater values, matrix is moved in upper left corner and scaling is not correct...

Someone has an idea?

thanks in advance,
best,
uki

here is the code:


int resolution=1;

void setup(){
 size(400, 400);
 background (0);
 noStroke();
 smooth();
 ellipseMode(CENTER);
}

void keyPressed() {
 if (key == CODED) {
   if (keyCode == UP) {
     resolution ++;
   }
   else if (keyCode == DOWN) {

     resolution--;
   }
   if(resolution < 0){
     resolution=0;

   }
 }
}
void draw(){
 background(0);

 float MatriceX[] = new float [resolution];
 float MatriceY[] = new float [resolution];
 
 for (int i=0;i<resolution; i++){
   for (int j=0; j<resolution; j++){
   
     float ratio=width/resolution;
     float ratio2 = ratio/2;
     
     MatriceX[i]=i*ratio;
     MatriceY[j]=j*ratio;

     ellipse(MatriceX[i]+ratio2,MatriceY[j]+ratio2,ratio2,ratio2);

   }
 }

}
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toxi
Re: matrix scale
Reply #1 - Dec 2nd, 2006, 1:39am  
A true classic...

Code:
float ratio=width/resolution;

In this line you would expect the "ratio" to be a floating point number as expected (and it is) - however both other arguments ("width" and "resolution") of the equation are integers... so the division will still happen in the integer domain! The casting to "float" is only done with the already computed result.

You on the other hand need to force the virtual machine to execute the equation already in the "float" domain by casting one of the arguments to be interpreted as "float":

Code:
float ratio=(float)width/resolution;

hth!
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ukicar
Re: matrix scale
Reply #2 - Dec 2nd, 2006, 3:17pm  
yes, a true classic error...

thank you very much toxi!

best
uki
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