Ulam Spiral in Processing

/*

So I found the YouTube Channel of ViHart. She's got these
quirky, awesome math videos involving lots of doodles.
Her most recent video is on the Ulam Spiral, so I thought
I would try to recreate it in processing.

Enjoy. Here's the video of her drawing.

http://www.youtube.com/watch?v=Yhlv5Aeuo_k

*/

void setup() {
    size(400, 400);
    background(255);
}

void draw() {
    int cy = height /  2;
    int cx = width / 2;
    int points = 10000000;

    int[][] direction = { {0,1},  // Down
                          {1,0},  // Right
                          {0,-1}, // Up
                          {-1,0}  // Left
    };

    int stretch = 0;
    int repeater = 2;
    int current_direction = 0;
    for (int i = 1; i <= points; i++) {
        if (isPrime(i)) {
            point(cx, cy);
        }

        cx += direction[current_direction][0];
        cy += direction[current_direction][1];
        stretch += 1;

        if (stretch * 2 == repeater) {
            current_direction = (current_direction + 1) % 4;
        }
        
        if (stretch == repeater) {
            current_direction = (current_direction + 1) % 4;
            repeater += 2;
            stretch = 0;
        }
    }
}

boolean isPrime(int n) {
    if (n <= 1)     return false;
    if (n == 2)     return true;
    if (n % 2 == 0) return false;

    int m = (int)sqrt(n);
    for (int i = 3; i <= m; i += 2) {
        if (m % i == 0) {
            return false;
        }
    }

    return true;
}

1. igoumeninja likes this
2. jcchurch posted this