<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);
function desenhaCirculo(evento) {
var x = evento.pageX - tela.offsetLeft;
var y = evento.pageY - tela.offsetTop;
pincel.fillStyle = "blue";
pincel.beginPath();
pincel.arc(x, y, 10, 0, 2 * 3.14);
pincel.fill();
console.log(x + ' , ' + y);
}
tela.onclick = desenhaCirculo;
</script>
