旋转
所述 2D 上下文的 rotate(r) 方法通过旋转的规定量 r 画布弧度围绕原点。
HTML
<canvas id="canvas" width=240 height=240 style="background-color:#808080;">
</canvas>
<button type="button" onclick="rotate_ctx();">Rotate context</button>
使用 Javascript
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var ox = canvas.width / 2;
var oy = canvas.height / 2;
ctx.font = "42px serif";
ctx.textAlign = "center";
ctx.textBaseline = "middle";
ctx.fillStyle = "#FFF";
ctx.fillText("Hello World", ox, oy);
rotate_ctx = function() {
// translate so that the origin is now (ox, oy) the center of the canvas
ctx.translate(ox, oy);
// convert degrees to radians with radians = (Math.PI/180)*degrees.
ctx.rotate((Math.PI / 180) * 15);
ctx.fillText("Hello World", 0, 0);
// translate back
ctx.translate(-ox, -oy);
};