每次鼠标移动时,我都需要帮助旋转一个矩形以指向屏幕上的鼠标。我一直在尝试使用 onmousemove 事件并计算度数/角度,然后转换为弧度,但由于某种原因,当我将弧度变量 rad 放在 rotate(); 中时,矩形根本不旋转。
<!DOCTYPE html>
<html>
<head>
<title>Rotate Rectangle Project</title>
<style>
canvas {
background:#f05424; display: block; margin: 0 auto;
}
body {
margin: 0px;
padding: 0px;
}
</style>
</head>
<body>
<canvas id="myCanvas" width=500 height=500 top=10px></canvas>
<p id='coord'>0</p>
<p id='degree'>0</p>
<p id='radian'>0</p>
<script>
var canvas = document.getElementById('myCanvas');
var ctx = canvas.getContext("2d");
var x = 100;
var y = 100;
var w = 100;
var h = 30;
var rX, rY, mX, mY, degrees, rad, coords;
document.onmousemove = function(e){
rX =533;
rY =100;
mX = e.clientX;
mY = e.clientY;
coords = mX + ',' + mY;
degrees = mY - rY + mX - rX;
rad = Math.atan2(mY - rY, mX - rX)* Math.PI/180;
draw();
document.getElementById('coord').innerHTML = coords;
document.getElementById('degree').innerHTML = degrees;
document.getElementById('radian').innerHTML = rad;
};
function rectangle(){
ctx.beginPath();
ctx.translate(x, y);
ctx.rotate(rad);
ctx.translate(-x, -y);
ctx.rect(x, y, w, h);
ctx.fillStyle = '#f8c778';
ctx.fill();
ctx.closePath();
}
function draw(){
ctx.clearRect(x,y,canvas.width,canvas.height);
rectangle();
}
</script>
</body>
</html>