U_Tokyo2016.pde

// http://qiita.com/massa142/items/3285a1b1ed12a6ab0299

void setup() {
  size(500, 500);
}

void plot() {
  float x = random(-2, 2);
  float y = random(-2, 2);
  PVector P = new PVector(x, y);
  PVector Q = new PVector(-x, -y);
  PVector R = new PVector(1, 0);
  PVector PQ = PVector.sub(Q, P);
  PVector PR = PVector.sub(R, P);
  PVector QP = PVector.sub(P, Q);
  PVector QR = PVector.sub(R, Q);
  PVector RP = PVector.sub(P, R);
  PVector RQ = PVector.sub(Q, R);
  float p = PVector.angleBetween(PQ, PR);
  float q = PVector.angleBetween(QP, QR);
  float r = PVector.angleBetween(RP, RQ);
  if (p < PI/2 && q < PI/2 && r < PI/2) {
    stroke(255, 0, 0);
  } else {
    stroke(0);
  }
  float gx = map(x, -2, 2, 0, width);
  float gy = map(y, -2, 2, height, 0);
  point(gx, gy);
}

void draw() {
  for (int i = 0; i < 1000; i++) {
    plot();
  }
}