void setup()
{
  size(300, 300);
  background(255);
  frameRate(6);
  smooth();
  rectMode(CENTER);
}

void draw()
{
	// choose a random stroke color
	int r = int(random(0, 255));
	int g = int(random(0, 255));
	int b = int(random(0, 255));
	// and fill opacity
	int opacity = int(random(100, 255));
	int nSides = int(random(3, 9));
  
	// determine the center x and y coordinates
	int cx = 25 + 50 * int(random(0, 6));
	int cy = 25 + 50 * int(random(0, 6));
  
	// if a random number (0 or 1) is 0, draw a polygon;
	// otherwise, draw a star
	boolean isPolygon = int(random(2)) == 0;
  
	// for stars, you need the proportion of short to long radius
	float proportion;
  
	stroke(255); // erase any previous drawing in this area
	fill(255);
	rect(cx, cy, 50, 50); 
    
	stroke(r, g, b);
	fill(r, g, b, opacity);
	if (isPolygon)
		{
			polygon(nSides, cx, cy, 24);
		}
	else
		{
			proportion = random(0.2, 0.8) * cos(PI / nSides);
			star(nSides, cx, cy, 24, proportion);
		}
}

void polygon(int n, float cx, float cy, float w, float h, float startAngle)
{
	if (n > 2)
		{
			float angle = TWO_PI/ n;
			w = w / 2.0;
			h = h / 2.0;
			beginShape();
			for (int i = 0; i < n; i++)
				{
					vertex(cx + w * cos(startAngle + angle * i),
					cy + h * sin(startAngle + angle * i));
				}
			endShape(CLOSE);
		}
}

void polygon(int n, float cx, float cy, float r)
{
	polygon(n, cx, cy, r * 2.0, r * 2.0, 0.0);
}

void star(int n, float cx, float cy, float r, float proportion)
{
	star(n, cx, cy, 2.0 * r, 2.0 * r, 0.0, proportion);
}

void star(int n, float cx, float cy, float w, float h,
	float startAngle, float proportion)
{
	if (n > 2)
		{
			float angle = TWO_PI/ (2 *n);  // twice as many sides
 			float dw; // draw width
			float dh; // draw height
			w = w / 2.0;
			h = h / 2.0;
  			beginShape();
			for (int i = 0; i < 2 * n; i++)
				{
					dw = w;
					dh = h;
  					if (i % 2 == 1)
						{
							dw = w * proportion;
							dh = h * proportion;
  						}
					vertex(cx + dw * cos(startAngle + angle * i),
					cy + dh * sin(startAngle + angle * i));
				}
			endShape(CLOSE);
		}
}