the code below displays a radial gradient filled rectangle. If I un-comment the two lines that set canvas’ width and height, it displays a black rectangle instead of a gradient filled one. why? how to set the width and height and still be able to show a gradient?
<!DOCTYPE HTML>
<html lang="en">
<head>
<meta charset="utf-8" />
<script type="text/javascript">
function on_load(e) {
var container = document.getElementById("container");
var canvas = container.appendChild(document.createElement("canvas"));
var context = canvas.getContext("2d");
var gradient = context.createRadialGradient(30, 30, 10, 30, 30, 30);
gradient.addColorStop(0, "rgba(0,0,0,1)");
gradient.addColorStop(1, "rgba(0,0,0,0)");
context.fillStyle = gradient;
//canvas.width = 150;
//canvas.height = 150;
context.fillRect(0, 0, 60, 60);
}
</script>
</head>
<body onload="on_load()"><div id="container"></div></body>
</html>
You have to change canvas size before using its context