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[英]How do I get my canvas image to rotate 90 degrees each time, its only rotating 180 degrees
[英]How can I rotate a Canvas containing an Image by 90, 180, 270 Degrees?
我有一个包含图像的HTML5画布。 现在,我想将此画布旋转x度。
我所做的是:
function getRadianAngle(degreeValue) {
return degreeValue * Math.PI / 180;
}
var rotateCanvas = function(canvas, image, degrees) {
var context = canvas.getContext('2d');
context.rotate(getRadianAngle(degrees));
context.drawImage(image, 0, 0);
return canvas;
}
var image = new Image();
image.onload = function() {
var canvas = document.createElement("canvas");
var context = canvas.getContext('2d');
var cw = canvas.width = image.width;
var ch = canvas.height = image.height;
context.drawImage(image, 0, 0, image.width, image.height);
rotateCanvas(canvas, image, 180);
}
image.src = // some image url;
此代码无法正常工作。
如何定义旋转画布的旋转功能?
编辑:我不想使用CSS,因为我需要画布进行进一步处理。
可以使用CSS来完成画布的旋转,但是如果画布是矩形而不是正方形,则可能会使页面设计混乱。
最好在画布上旋转图像。
示例代码和演示: http : //jsfiddle.net/m1erickson/8uRaL/
顺便说一句,所需角度的弧度为:
示例代码:
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
canvas{border:1px solid red;}
</style>
<script>
$(function(){
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var radians=0;
var img=new Image();
img.onload=start;
img.src="https://dl.dropboxusercontent.com/u/139992952/stackoverflow/cat.png";
function start(){
animate();
}
function animate(){
requestAnimationFrame(animate);
ctx.clearRect(0,0,canvas.width,canvas.height);
ctx.save();
ctx.translate(canvas.width/2,canvas.height/2);
ctx.rotate(radians);
ctx.drawImage(img,-img.width/2,-img.height/2);
ctx.restore();
radians+=Math.PI/180;
}
}); // end $(function(){});
</script>
</head>
<body>
<canvas id="canvas" width=300 height=300></canvas>
</body>
</html>
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