void setup() {
    size(800, 600);
}
int x = 0;
float y = 0;

void draw() {
    if (x % 3 == 0) {
        stroke(0);
    } else if (x % 3 == 1) {
        stroke(150);
    }  else {
        stroke(230);
    }

    line(x, 0, x, y);
    x+= 1;
    y+= 0.5;
}