sin是这个角的对边和斜边的比。
cos一是这个角挨着的那条边和斜边的比；tan是这个角的对边和邻边的比。
在平面直角坐标系xOy中设∠β的始边为x轴的正半轴，设点P（x，y）为∠β的终边上不与原点O重合的任意一点，设r=OP，令∠β=∠α，则：sin a=y/r；cos a=x/r。
2 π == 360度
const a = Math.sin(num * π / 180) == BC / AC
const b = Math.cos(num * π / 180 ) = AB/ AC
公式原理
js实现圆周运动
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| <!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Document</title>
<style>
* {
margin: 0;
padding: 0;
}
.circle {
position: absolute;
left: 500px;
top: 500px;
border: 2px solid red;
border-radius: 50%;
margin-left: -150px;
margin-top: -150px;
width: 300px;
height: 300px;
}
.rect {
position: absolute;
width: 10px;
height: 10px;
background-color: blue;
top: 350px;
left: 500px;
}
.red{
background: red;
}
.blue{
background-color: blue;
}
.orange{
background-color: orange;
}
.black{
background-color: black;
}
.pink{
background-color: pink;
}
</style>
</head>
<body>
<div class="circle"></div>
<div class=" rect rect1 red"></div>
<div class="rect rect2 blue"></div>
<div class="rect rect3 orange"></div>
<div class="rect rect4 black"></div>
<div class="rect rect5 pink"></div>
</body>
</html>
<script>
(function () {
/*
普通使用
var num = 0;
var circle = document.querySelector(".circle");
var middleX = circle.offsetLeft + circle.offsetWidth / 2;
var middleY = circle.offsetTop + circle.offsetHeight / 2;
function ani() {
if (num === 360) {
num = 0;
} else {
num++;
}
var line1Y = Math.sin((num * Math.PI) / 180) * 150;
var line2X = Math.cos((num * Math.PI) / 180) * 150;
console.log(line1Y, line2X);
document.querySelector(".rect").style.cssText = `;left:${
line2X + middleX
}px;top:${line1Y + middleY}px`;
}
ani();
setInterval(ani, 100); */
class AniClass {
constructor() {
this.num = 0;
this.circle = document.querySelector(".circle");
this.middleX = this.circle.offsetLeft + this.circle.offsetWidth / 2;
this.middleY = this.circle.offsetTop + this.circle.offsetHeight / 2;
}
ani(className, delay) {
this.move(className);
setTimeout(()=>{
setInterval(this.move.bind(this,className), 50);
},delay)
}
move(className){
if (this.num === 360) {
this.num = 0;
} else {
this.num++;
}
var line1Y = Math.sin((this.num * Math.PI) / 180) * 150;
var line2X = Math.cos((this.num * Math.PI) / 180) * 150;
document.querySelector(className).style.cssText = `;left:${
line2X + this.middleX
}px;top:${line1Y + this.middleY}px`;
}
}
[1,2,3,4,5].forEach(item=>{
const Ani = new AniClass();
Ani.ani('.rect'+item,4000*item);
});
})();
</script>
|
