<!DOCTYPE html>
<html>
<body>
<canvas id='drawCanvas' width='200' height='200' >
<script>
var drawCanvas;
var drawCtx;
var testCanvas;
var testCtx;
var rotateNum = 0;
function draw() {
drawCtx.clearRect(0, 0, drawCanvas.width, drawCanvas.height);
for (var i = 0; i < 4; i++) {
for (var j = 0; j < 4; j++) {
drawCtx.fillStyle = 'rgb(' + (255 - 40 * i - 2 * rotateNum) + ',' + (255 - 50 * j)
+ ',' + (255 - 12 * rotateNum)+ ')';
drawCtx.fillRect(j * 50, i * 50, 50, 50);
rotateNum = (rotateNum + 1) % 20;
}
}
requestAnimationFrame(draw);
}
function changeTestCanvas() {
testCtx.clearRect(0, 0, testCanvas.width, testCanvas.height);
testCtx.fillStyle = 'rgb(' + (255 - 12 * rotateNum) + ',' + (255 - 12 * rotateNum)
+ ',' + (255 - 12 * rotateNum) + ')';
testCtx.fillRect(0, 0, 4000, 4000);
}
function runTest() {
changeTestCanvas();
testCanvas.toBlob(function(blob) {
runTest();
});
}
window.onload = function () {
drawCanvas = document.getElementById("drawCanvas");
drawCtx = drawCanvas.getContext("2d");
testCanvas = document.createElement("canvas");
testCanvas.width = 4000;
testCanvas.height = 4000;
testCtx = testCanvas.getContext("2d");
draw();
runTest();
};
</script>
</body>
</html>