// draw polygons using lines

void setup() { // all sketch setup goes here
  size(400, 400);
  smooth();
  background(255);
} // setup() 

void draw() {
} // draw()

void mousePressed() {
  drawPolygon(mouseX, mouseY, random(20, 80), int(random(3, 12)));
} // mousePressed()

/** Draw a polygon based on the center point, size and number of sides.
 *
 * @param cx x coordinate
 * @param cy y coordinate
 * @param sz size
 * @param nSides number of sides
 */ 
void drawPolygon(float cx, float cy, float sz, int nSides) {
  // draw a hexagon centered at cx, cy
  float x1, y1, x2, y2;
  float radius = sz/2;
  float theta = 0.0;
  float delta = 360.0/nSides;

  point(cx, cy);

  // compute x1, y1
  x1 = cx + radius;
  y1 = cy;
  for (int i = 0; i < nSides; i++) {
    theta = theta + delta;
    x2 = cx + radius * cos(radians(theta));
    y2 = cy - radius * sin(radians(theta));
    line(x1, y1, x2, y2);

    // copy x2, y2 into x1, y1
    x1 = x2;
    y1 = y2;
  }
} // drawPolygon