<canvas width="600" height="400"></canvas>
<script>
var tela = document.querySelector('canvas');
var pincel = tela.getContext('2d');
pincel.fillStyle = 'grey';
pincel.fillRect(0, 0, 600, 400);
var cores = ['blue','red','green'];
var indice = 0;
function desenhaCirculo(evento){
var x = evento.pageX - tela.offsetLeft;
var y = evento.pageY - tela.offsetTop;
pincel.fillStyle = cores[indice];
pincel.beginPath();
pincel.arc(x, y, 10, 0, 2 * 3.14);
pincel.fill();
console.log( x + ','+ y);
}
tela.onclik = desenhaCirculo;
function alteraCor(){
indice++;
if(indice >= cores.length){
indice = 0;
}
//alert(indice);
return false;
}
tela.oncontextmenu = alteraCor;
</script>