画布翻译(Canvas Translation)
HTML5画布提供translate(x, y)方法，该方法用于将画布及其原点移动到网格中的不同点。
这里参数x是画布向左或向右移动的量，y是向上或向下移动的量。
例子 (Example)
以下是一个简单的例子，利用上述方法绘制各种螺旋形图 -
<!DOCTYPE HTML>
<html>
<head>
<style>
#test {
width:100px;
height:100px;
margin:0px auto;
}
</style>
<script type = "text/javascript">
function drawShape() {
// get the canvas element using the DOM
var canvas = document.getElementById('mycanvas');
// Make sure we don't execute when canvas isn't supported
if (canvas.getContext) {
// use getContext to use the canvas for drawing
var ctx = canvas.getContext('2d');
ctx.fillRect(0,0,300,300);
for (i = 0;i<3;i++) {
for (j = 0;j<3;j++) {
ctx.save();
ctx.strokeStyle = "#FF0066";
ctx.translate(50+j*100,50+i*100);
drawSpirograph(ctx,10*(j+3)/(j+2),-2*(i+3)/(i+1),10);
ctx.restore();
}
}
} else {
alert('You need Safari or Firefox 1.5+ to see this demo.');
}
}
function drawSpirograph(ctx,R,r,O) {
var x1 = R-O;
var y1 = 0;
var i = 1;
ctx.beginPath();
ctx.moveTo(x1,y1);
do {
if (i>20000) break;
var x2 = (R+r)*Math.cos(i*Math.PI/72) - (r+O)*Math.cos(((R+r)/r)*(i*Math.PI/72))
var y2 = (R+r)*Math.sin(i*Math.PI/72) - (r+O)*Math.sin(((R+r)/r)*(i*Math.PI/72))
ctx.lineTo(x2,y2);
x1 = x2;
y1 = y2;
i++;
} while (x2 != R-O && y2 != 0 );
ctx.stroke();
}
</script>
</head>
<body id = "test" onload = "drawShape();">
<canvas id = "mycanvas" width = "400" height = "400"></canvas>
</body>
</html>
以上示例将产生以下结果 -
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