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How to make elements move along a parabolic trajectory in JS
- php中世界最好的语言Original
- 2018-04-14 11:19:322731browse
This time I will show you how to use JS to make elements move along a parabolic trajectory. What are the precautions for using JS to make elements move along a parabolic trajectory? The following is a practical case. Let’s take a look. one time.
The general idea of implementing the parabolic trajectory motion of the ball in js:
1. Use the setInterval() method to perform interval refresh and update the ball position to achieve dynamic effects
2. Draw the ball and the sports area. The sports area can be vertically centered through flex layout
3. Use the physical formula S(y)=1/2*g*t*t, S(x)=V(x)t to calculate the path
It is now determined that V(x)=4m/s, and the refresh time interval is set to 0.1s. Originally, the conversion between px and meters is different for different sizes. In this example, a 17-inch monitor is used, which is about 1px=0.4mm. However, the browser is too small, so it can only simulate a parabolic trajectory. In this example, the distance between px and meters is reduced to 100 times.
The first type: draw the ball through border-radius
Idea: Use border-radius: 50% to draw the ball, set relative to the ball, calculate the current position of the ball each time, and assign it to top and left. When calculating the motion trajectory, the variable can be incremented to calculate the number of setInterval calls, each time is 0.1s, so that the total time can be calculated. The code is as follows:
<!DOCTYPE>
<html>
<head>
<meta http-equiv="Content-type" content="text/html; charset=utf-8" />
<title></title>
<style type="text/css">
/*给body进行flex布局，实现垂直居中*/
body {
min-height: 100vh;/*高度适应浏览器高度*/
display: flex;
justify-content: center;/*水平居中*/
align-items: center;/*垂直居中*/
font-size: 20px;
font-weight: bold;
}
/*设置运动区域*/
#bg {
width: 600px;
height: 600px;
border: 2px solid #e0e0e0;
border-radius: 4px;/*给p设置圆角*/
padding: 20px;
}
/*生成小球，并定义初始位置*/
#ball {
border-radius: 50%;/*可把正方形变成圆形，50%即可*/
background: #e0e0e0;
width: 60px;
height: 60px;
position: relative;
top: 30px;
left: 30px;
}
button {
width: 80px;
height: 30px;
border-radius: 4px;
color: #fff;
background: #AA7ECC;
font-size: 20px;
font-weight: bold;
margin-left: 20px;
}
</style>
</head>
<body>
<p id="bg">
此时水平速度为：4<button onclick="start()">演示</button>
<p id="ball"></p>
</p>
<script type="text/javascript">
function start(){
var x,y,k=1,t;
//x是水平方向移动路径；y是垂直方向的；k记录次数，可与0.1相乘得时间；t记录setInterval的返回id，用于clearInterval
t = setInterval(function(){
x = 30+0.1*k*4*100;
//S(x)=S(0)+t*V(x)，100是自定义的米到px转换数
y = 30+1/2*9.8*0.1*k*0.1*k*100;//S(y)=S(0)+1/2*g*t*t
var j = document.getElementById("ball");
//通过修改小球的top和left，修改小球的位置
j.style.top = y;
j.style.left = x;
k++;//每次调用，k自增，简化计算
if(x>480||y>480){
clearInterval(t);//小球达到边界时，清除setInterval
}
},100);//每0.1s调用一次setInterval的function
}
</script>
</body>
</html>
Second type: canvas in h5 draws the ball and movement area
Idea: Use canvas to draw the ball. Since the ball cannot move through top and left, it needs to clear the canvas with clearRect every time it is called, and then draw the ball with the calculated position. The code is as follows:
<!DOCTYPE>
<html>
<head>
<meta http-equiv="Content-type" content="text/html; charset=utf-8" />
<title></title>
<style type="text/css">
body {
min-height: 100vh;
display: flex;
justify-content: center;
align-items: center;
}
#myCanvas {
box-shadow: -2px -2px 2px #efefef,5px 5px 5px #b9b9b9;
}
</style>
</head>
<body>
<canvas id="myCanvas" width="600px" height="600px"></canvas>
<script type="text/javascript">
var x=50,y=50,k=1;
var c=document.getElementById("myCanvas");
var cxt=c.getContext("2d");
cxt.fillStyle="#e0e0e0";
cxt.beginPath();
cxt.arc(x,y,30,0,Math.PI*2,true);
cxt.closePath();
cxt.fill();
t=setInterval("parabola()",100);
function parabola(){
cxt.clearRect(0,0,600,600);//清除原始图形
cxt.beginPath();
x=50+0.1*k*4*100;y=50+9.8*0.1*k*0.1*k*1/2*100;
cxt.arc(x,y,30,0,Math.PI*2,true);
cxt.closePath();
cxt.fill();
k++;
if(x>520||y>520){
clearInterval(t);
}
}
</script>
</body>
</html>
Both methods can be implemented. The calculation method is the same, but the method is different. The first one is partial to CSS, using border-radius and dynamically modifying the DOM. The second one uses canvas to draw graphics. The drawing process should be carefully studied.
I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!
Recommended reading:
Detailed explanation of the use of mobile component library cube-ui
JS class, constructor, factory function Instructions
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