Drawing state restore
In this chapter you will learn:
Saving and Restoring Drawing State
We can save the drawing state and return to it later using the following methods: The saved drawing states are stored in a stack.
| Value | Description |
|---|---|
| save() | Saves the values for the drawing state properties |
| restore() | Pops the first set of values from the state stack |
Demo for saving and restoring drawing state
<!DOCTYPE HTML><!--from jav a 2s . c o m-->
<html>
<head>
<style>
canvas {
border: thin solid black;
margin: 4px
}
</style>
</head>
<body>
<canvas id="canvas" width="500" height="140" preload="auto">
Your browser doesn't support the <code>canvas</code> element
</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>
Next chapter...
What you will learn in the next chapter:
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