Save and restore Canvas states with button action in JavaScript
Description
The following code shows how to save and restore Canvas states with button action.
Example
<!--from w ww. ja va2s . c o m-->
<!DOCTYPE HTML>
<html>
<head>
</head>
<body>
<canvas id="canvas" width="500" height="140" preload="auto"></canvas>
<div>
<button>Save</button>
<button>Restore</button>
</div>
<script>
var ctx = document.getElementById("canvas").getContext("2d");
var grad = ctx.createLinearGradient(500, 0, 500, 140);
grad.addColorStop(0, "red");
grad.addColorStop(0.5, "white");
grad.addColorStop(1, "black");
var colors = [ "blue", grad, "red", "green", "yellow", "black", "grey" ];
var cIndex = 0;
ctx.fillStyle = colors[cIndex];
draw();
var buttons = document.getElementsByTagName("button");
for ( var i = 0; i < buttons.length; i++) {
buttons[i].onclick = handleButtonPress;
}
function handleButtonPress(e) {
switch (e.target.innerHTML) {
case 'Save':
ctx.save();
cIndex = (cIndex + 1) % colors.length;
ctx.fillStyle = colors[cIndex];
draw();
break;
case 'Restore':
cIndex = Math.max(0, cIndex - 1);
ctx.restore();
draw();
break;
}
}
function draw() {
ctx.fillRect(0, 0, 500, 400);
}
</script>
</body>
</html>
The code above generates the following result.
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