Don’t see anything? Believe it or not, there really is a <canvas> in the blank white space above this text. Try clicking on it and see what happens. The <canvas> detects the click and draws a circle at the click coordinates. The drawSpiral subroutine takes care of all the rest.
The <canvas> in the blank white space above this text also detects clicks and draws a circle at the click coordinates—but the spiral effect is different. I draw the circles behind the scaled and rotated image from the offscreen <canvas> instead of in front; I scale the images larger instead of smaller; and I apply a globalAlpha of 0.95 to the offscreen context to make the images translucent.