我如何旋转矩形以指向鼠标

Question

每次鼠标移动时，我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 degrees/angle，然后转换为弧度，但出于某种原因，当我将弧度变量 rad 放入 rotate(); 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>

Answer 1

我已经编辑了你的代码，基本上你需要在 onmousemove 上调用 rectangle 并清除 canvas。

var canvas = document.getElementById('myCanvas');
var ctx = canvas.getContext("2d");
var x = 100;
var y = 100;
var w = 100;
var h = 30;
var mouseX, mouseY, degrees, rad, coords;

document.onmousemove = function(e) {
  mouseX = e.clientX;
  mouseY = e.clientY;
  coords = mouseX + ',' + mouseY;
  degrees = mouseY - y + mouseX - x;
  rad = Math.atan2(mouseY - y, mouseX - x) * (180 / Math.PI);
  rectangle();
};



function rectangle() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  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();
}

body {
  margin: 0px;
  padding: 0px;
}

canvas {
  background: #f05424;
  display: block;
  margin: 0 auto;
}

<canvas id="myCanvas" width=500 height=500></canvas>

我如何旋转矩形以指向鼠标

how do i rotate a rectangle to point towards mouse

javascript

mouse

rotation

atan2