HTML5画布转换矩阵
HTML5canvas提供了允许直接修改转换矩阵的方法。转换矩阵最初必须是身份转换。然后可以使用转换方法对其进行调整。
t变换(m11,m12,m21,m22,dx,dy)方法必须将当前变换矩阵与-所描述的矩阵相乘
m11 m21 dx m12 m22 dy 0 0 1
的setTransform(M11,M12,M21,M22,DX,DY) 的方法必须重置当前变换单位矩阵，然后调用与相同参数的变换(M11,M12,M21,M22,DX,DY)方法。
<!DOCTYPE HTML>
<html>
<head>
<script>
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');
var sin = Math.sin(Math.PI/6);
var cos = Math.cos(Math.PI/6);
ctx.translate(200, 200);
var c = 0;
for (var i=0; i <= 12; i++) {
c = Math.floor(255 / 12 * i);
ctx.fillStyle = "rgb(" + c + "," + c + "," + c + ")";
ctx.fillRect(0, 0, 100, 100);
ctx.transform(cos, sin, -sin, cos, 0, 0);
}
ctx.setTransform(-1, 0, 0, 1, 200, 200);
ctx.fillStyle = "rgba(100, 100, 255, 0.5)";
ctx.fillRect(50, 50, 100, 100);
} else {
alert('You need Safari or Firefox 1.5+ to see this demo.');
}
}
</script>
</head>
<body onload="drawShape();">
<canvas id = "mycanvas" width = "400" height = "400"></canvas>
</body>
</html>