super quick super easy envelope

mathEnvelope1.pde

/*
gotta implement this
 http://mathgifs.blogspot.com/2013/12/mathematical-envelopes.html
 doin' it for the pretty picturez!
 (and the math. yeah. the math.)
 */

float theta;
PVector p0, p1;
float multiplicity;
int r = 100;

void setup() {
  size(300, 300, P2D);
  frameRate(30);
  background(0);
  p0 = new PVector(0,0);
  p1 = new PVector(0,0);
  theta = 0.1;
  setMult();
  shift();
}

void draw() {
  if (p0.x != p1.x && p0.y != p1.y) {
    stroke(255,100);
    translate(width/2, height/2);
    line(p0.x, p0.y, p1.x, p1.y);
    shift();
    theta += 0.1;
  }
}

void setPt(PVector p, float increment) {
  float inc = increment%TWO_PI;
  p.x = r*cos(inc);
  p.y = r*sin(inc);
}

void shift() {
  setPt(p0, theta);
  setPt(p1, theta*multiplicity);
}

void setMult() {
  multiplicity = random(1, 4);
  text("one endpoint is moving "+multiplicity+" times \nas fast as the other",0,20);
  text("click to change ratio",0,height-20);
}

void mousePressed() {
  background(0);
  setMult();
}