html canvas overlay 2
var context = document.getElementById('cvs').getContext('2d');
// Draw a red square
context.fillStyle = 'red';
context.fillRect(50,50,100,100);
// Change the globalCompositeOperation to destination-over so that anything
// that is drawn on to the canvas from this point on is drawn at the back
// of what's already on the canvas
context.globalCompositeOperation = 'destination-over';
// Draw a big yellow rectangle
context.fillStyle = 'yellow';
context.fillRect(0,0,600,250);
// Now return the globalCompositeOperation to source-over and draw a
// blue rectangle
context.globalCompositeOperation = 'source-over';
// Draw a blue rectangle
context.fillStyle = 'blue';
context.fillRect(75,75,100,100);