<canvas width="1500" height="700"></canvas>
<script>
var tela = document.querySelector("canvas");
var pincel = tela.getContext("2d");
pincel.fillStyle = "black";//"black" = preto;
pincel.fillRect(0, 0, 1500, 700);
function desenhaCirculo(evento) {
var x = evento.pageX - tela.offsetLeft;
x = evento.pageX - tela.offsetRight;
var y = evento.pageY - tela.offsetTop;
y = evento.pageY - tela.offsetBottom;
pincel.fillStyle = "green";//"green" = verde;
pincel.beginPath();
pincel.arc(x, y, 20, 0, 2 * 3.14);
pincel.fill();
console.log(x + ", " + y);
}
tela.onclick = desenhaCirculo;
</script>
