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Index › Programming Questions & Help › Syntax Questions › Stuck and Seeking Solution
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Stuck and Seeking Solution (Read 213 times)
nimkintz
Stuck and Seeking Solution
Feb 18th, 2009, 12:27am  
Hey,
I'm trying to build a stripe generator that will pull colors from an array and use the 3 or 4 colors I set to randomly fill my canvas with vertical stripes.  I've got the code set to actually make the stripes, but I can't figure out how to have the colors pulled from the array.

When I have it generate any number of stripes greater than the colors I have set, it crashes.

Here is what I have:

int y;
float speedX = 3.0;
int shapes = 3;
float[]x = new float[shapes];
float[]w = new float[shapes];
float[]h = new float[shapes];
color c1 = #040A27;
color c2 = #17204B;
color c3 = #4C5A9B;
color[]colors = {c1, c2, c3};  // max colors = number of shapes
void setup(){
 size(400, 400);
 frameRate(30);
 noStroke();
 // fill arrays will random values
  for (int i=0; i<shapes; i++){
    x[i]=random(width);
    w[i]=random(15)+4;
    h[i]=w[i];
    //colors[i]=color();
  }
}

void draw(){
 for (int i=0; i<shapes; i++){
   fill(colors[i]);
   rect(x[i], y, w[i], h[i]);
 }
 y+=speedX;
}

and this just creates three random stripes.  Somehow I got to a point where it filled the canvas with shades of grey but I want 3 shades of red, or 3 shades of blue, etc.

Thanks for any help you can give to get me moving again.

Jeff
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danielle
Re: Stuck and Seeking Solution
Reply #1 - Feb 18th, 2009, 1:48am  
You get an array index out of bounds, because you are attempting to access an element of the colors[] array greater than [0],[1],or [2]. So if you want to get the color for shape 100, you need to make sure you are still choosing either [0],[1],or [2].

Look up the mod operator (%) (which, in my experience teaching programming, some people have a hard time wrapping their head around). x%y = the remainder of x divided by y. This causes numbers to "fold" back around when you are incrementing. So if you do x%3, no matter what x is, you will get zero, one, or two.

So change the fill command in your draw() loop to:

fill(colors[i%3]);

or, more robustly (in case you change the size of your colors array later):

fill(colors[i%colors.length]);

hope that was what you were looking for....
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cloister
Re: Stuck and Seeking Solution
Reply #2 - Feb 18th, 2009, 1:50am  
The problem is you're never checking the value of i against the bounds of the colors array.  Here's a working version with minimal changes:

int y;
float speedX = 3.0;
int shapes = 5;
int numColors = 3;
float[]x = new float[shapes];
float[]w = new float[shapes];
float[]h = new float[shapes];
color c1 = #040A27;
color c2 = #17204B;
color c3 = #4C5A9B;
color[]colors = {c1, c2, c3};  // max colors = number of shapes
void setup(){
 size(400, 400);
 frameRate(30);
 noStroke();
 // fill arrays will random values
  for (int i=0; i<shapes; i++){
    x[i]=random(width);
    w[i]=random(15)+4;
    h[i]=w[i];
    //colors[i]=color();
  }
}

void draw(){
 for (int i=0; i<shapes; i++){
   fill(colors[i % numColors]);
   rect(x[i], y, w[i], h[i]);
 }
 y+=speedX;
}
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nimkintz
Re: Stuck and Seeking Solution
Reply #3 - Feb 18th, 2009, 11:48pm  
Thanks to you both for the replies.  That did indeed work - perfect.  

Jeff
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