<script>
window.onload = function() {
var canvas = document.getElementById('quadro');
var ctx = canvas.getContext('2d');
ctx.beginPath();
ctx.moveTo(20,50);
ctx.strokeStyle = '#f00';
ctx.arcTo(100, 50, 100, 130, 80);
ctx.stroke();
ctx.beginPath();
ctx.moveTo(100,130);
ctx.strokeStyle = '#009';
ctx.arcTo(200, 130, 200, 30, 100);
ctx.stroke();
ctx.beginPath();
ctx.moveTo(200,30);
ctx.strokeStyle = '#090';
ctx.arcTo(200, 190, 380, 190, 180);
ctx.stroke();
}
</script>
canvas {border:1px solid #ccc;}
<canvas id="quadro" width="400" height="200"> <p>Conteúdo alternativo para navegadores que não suportam canvas.</p> </canvas>