How can I restrict a for-loop pattern to stay within a shape? Basically, how can I fill a shape with a pattern instead of a color? - for-loop

Question

I am trying to create concentric circles filled with lines moving in opposite directions (that follow the mouse). I can't figure out how to fill only the circles with the lines -- I used a for-loop to make lines, and want to cut them off outside of the radius of the circles. Basically, I am trying to fill the circles with a pattern of lines.
This is my code:
float r = 0;
float startAngle;
float density;
float radius;
void setup() {
size(500, 500);
background(255);
stroke(150, 0, 150);
}
void draw() {
int[] s = {
500, 325, 200, 100, 50, 25
};
for (int i = 0; i < 500; i = i+5) {
line(0, i, 500, i);
if(i > s[0]) {
noStroke();
}
}
translate(width/2, height/2);
rotate(r);
r = r + .01;
fill(0);
ellipse(0, 0, s[0], s[0]);
fill(50);
ellipse(0, 0, s[1], s[1]);
fill(100);
ellipse(0, 0, s[2], s[2]);
fill(150);
ellipse(0, 0, s[3], s[3]);
fill(200);
ellipse(0, 0, s[4], s[4]);
fill(255);
ellipse(0, 0, s[5], s[5]);
}
Any help would be appreciated!

Answer 1

It's hard to help with general "how do I do this" type questions. Stack Overflow is designed for more specific "I tried X, expected Y, but got Z instead" type questions. But I'll try to help in a general sense.
The best advice I can give you is to start smaller. Break your problem down into smaller pieces and take those pieces on one at a time.
For example, instead of starting with your whole program that shows multiple circles, why not start with a simpler example program that just shows a single circle? Try to get a pattern to display inside of that.
Like everything in programming, there are multiple ways to do that.
Option 1: You could probbaly use basic geometry and trig to figure out where the points should be on the circle, then draw them based on those points. The cos() and sin() functions would probably come in handy with this approach.
Option 2: You could also use image masking techniques. For example, you could create a texture of lines, and then use a circular mask to isolate a cirlce of those lines. The texture() function or the PImage#mask() functions would be your friends here.
Try out those approaches to see which one you like best. The Processing reference is your best friend: for example, here is a reference on the texture() function, and here is a reference on the PImage#mask() function. Then if you get stuck on a specific step, you can post a MCVE of just that step, and we'll go from there. Good luck.