目的:通过js实现小球碰撞并实现动量守恒
canvas我们就不多说了,有用着呢。
我们可以通过canvas画2D图形(圆、方块、三角形等等)3D图形(球体、正方体等待)。
当然这只是基础的皮毛而已,canvas的强大之处在于可以做游戏,导入模型,粒子效果,实现漫游又或者全景和VR。
这里我们介绍纯js写的2D小球碰撞。(主要是博主的Three.js不咋地)
好吧,老规矩,先上图!
额。。。很尴尬的是博主的截图功底不咋地,没有截下碰撞的瞬间。
话不多说,开始教程。
首先我们需要创建画布给它一个id方便后面监听处理。
<body>
<canvas id="myCanvas"></canvas>
</body>
然后是Js代码
//声明画布大小为屏幕的1/3
var width = window.innerWidth/3;
var height = window.innerHeight/3;
var canvas = document.getElementById("myCanvas");
canvas.width = width;
canvas.height = height;
//创建2d画笔
var ctx = canvas.getContext("2d");
//填充颜色设置为黑色(背景色)
ctx.fillStyle = "#000";
//将整个画布填充
ctx.fillRect(0,0,width,height);
这是Canvas最基本的操作,我们解释一下fillRect(x,y,width,height);这个函数。
x和y填充的起始坐标点,width和height是填充区域的宽和高。
由于我们创建的是带有物理性质的小球,所以我们用一个函数封装创建小球的代码。
以后创建小球直接调用它就行了。
function Ball(x,y,vx,vy,ax,ay,size,rou,color,ctx){
//参数传值
//x,y为坐标点 vx,vy为小球水平和垂直方向上的速度 ax,ay为加速度
//size 为大小 rou为密度 color颜色 ctx画笔
this.x = x;
this.y = y;
this.vx = vx;
this.vy = vy;
this.rou = rou;
this.size = size;
this.ax = ax;
this.ay = ay;
this.m = Math.PI*this.size*this.size*rou;//求出质量 this.draw = function(ctx){
ctx.fillStyle=color;
//console.log(this.x, this.y,this.size);
ctx.beginPath();
ctx.arc(this.x, this.y, this.size, 0, Math.PI*2,false);//画圆
ctx.fill();
ctx.closePath();
}
this.draw(ctx);
}
接下来实例化出两个小球。
//碰撞检测 动量守恒
//x,y,vx,vy,ax,ay,size,rou,color,ctx
var balla = new Ball(20,0.5*height,5,-3,0,0,8,1,"#ff0",ctx);
var ballb = new Ball(width-20,0.5*height,-3,5,0,0,13,1,"#0ff",ctx);
var ballc = new Ball(width/2,0.5*height,7,4,0,0,13,1,"#0ff",ctx);
然后我们封装了一个函数来实现小球是实时更新。
function animation(){ //小球的速度等于速度加上加速度
balla.vx+= balla.ax;
balla.vy+=balla.ay;
//小球的位移等于小球现在的坐标加上速度
balla.x+= balla.vx;
balla.y+=balla.vy; ballb.vx+= ballb.ax;
ballb.vy+=ballb.ay;
ballb.x+= ballb.vx;
ballb.y+=ballb.vy;
//基于距离的碰撞检测
var pointdis=(balla.x-ballb.x)*(balla.x-ballb.x)+(balla.y-ballb.y)*(balla.y-ballb.y);//坐标距离
var pointsize=(balla.size+ballb.size)*(balla.size+ballb.size);//半径距离
if( pointdis <= pointsize)
{
console.log("haha");
//这里是能量守恒公式
var ballavx =((balla.m-ballb.m)*balla.vx+2*ballb.m*ballb.vx)/(balla.m+ballb.m);
var ballavy =((balla.m-ballb.m)*balla.vy+2*ballb.m*ballb.vy)/(balla.m+ballb.m);
var ballbvx=((ballb.m-balla.m)*ballb.vx+2*balla.m*balla.vx)/(balla.m+ballb.m);
var ballbvy=((ballb.m-balla.m)*ballb.vy+2*balla.m*balla.vy)/(balla.m+ballb.m);
balla.vx = ballavx;
balla.vy = ballavy; ballb.vx = ballbvx;
ballb.vy = ballbvy;
//小Bug改进
if(Math.abs(balla.vx-ballb.vx)<0.01&&Math.abs(balla.vy-ballb.vy)<0.01)
{
console.log(balla.vx);
balla.vx=-balla.vx;
balla.vy=-balla.vy;
return;
}
} //判断是否碰撞到画布的边缘
if(balla.x+balla.size>=width||balla.x-balla.size<=0)
{
balla.vx*=-0.98;
}
if(balla.y+balla.size>=height||balla.y-balla.size<=0)
{
balla.vy*=-0.98;
} if(ballb.x+ballb.size>=width||ballb.x-ballb.size<=0)
{
ballb.vx*=-0.98;
}
if(ballb.y+ballb.size>=height||ballb.y-ballb.size<=0)
{
ballb.vy*=-0.98;
} //清空画布,画出小球
ctx.fillStyle = "#000";
ctx.fillRect(0,0,width,height);
balla.draw(ctx);
ballb.draw(ctx);
//console.log(ballb.vy); }
最后我们让他30毫秒更新一次。
setInterval(animation,30);
OK,又大功告成了。自己动手试试吧!
懒人福利!!!
完整代码。
<html>
<head>
<style>
body{margin:0;}
</style>
</head>
<body>
<canvas id="myCanvas"></canvas>
</body>
<script>
//声明画布大小为屏幕的1/3
var width = window.innerWidth/3;
var height = window.innerHeight/3;
var canvas = document.getElementById("myCanvas");
canvas.width = width;
canvas.height = height;
//创建2d画笔
var ctx = canvas.getContext("2d");
//填充颜色设置为黑色(背景色)
ctx.fillStyle = "#000";
//将整个画布填充
ctx.fillRect(0,0,width,height); //碰撞检测 动量守恒
//x,y,vx,vy,ax,ay,size,rou,color,ctx
var balla = new Ball(20,0.5*height,5,-3,0,0,8,1,"#ff0",ctx);
var ballb = new Ball(width-20,0.5*height,-3,5,0,0,13,1,"#0ff",ctx);
var ballc = new Ball(width/2,0.5*height,7,4,0,0,13,1,"#0ff",ctx); setInterval(animation,30);
function animation(){ //小球的速度等于速度加上加速度
balla.vx+= balla.ax;
balla.vy+=balla.ay;
//小球的位移等于小球现在的坐标加上速度
balla.x+= balla.vx;
balla.y+=balla.vy; ballb.vx+= ballb.ax;
ballb.vy+=ballb.ay;
ballb.x+= ballb.vx;
ballb.y+=ballb.vy;
//基于距离的碰撞检测
var pointdis=(balla.x-ballb.x)*(balla.x-ballb.x)+(balla.y-ballb.y)*(balla.y-ballb.y);//坐标距离
var pointsize=(balla.size+ballb.size)*(balla.size+ballb.size);//半径距离
if( pointdis <= pointsize)
{
console.log("haha");
//这里是能量守恒公式
var ballavx =((balla.m-ballb.m)*balla.vx+2*ballb.m*ballb.vx)/(balla.m+ballb.m);
var ballavy =((balla.m-ballb.m)*balla.vy+2*ballb.m*ballb.vy)/(balla.m+ballb.m);
var ballbvx=((ballb.m-balla.m)*ballb.vx+2*balla.m*balla.vx)/(balla.m+ballb.m);
var ballbvy=((ballb.m-balla.m)*ballb.vy+2*balla.m*balla.vy)/(balla.m+ballb.m);
balla.vx = ballavx;
balla.vy = ballavy; ballb.vx = ballbvx;
ballb.vy = ballbvy;
//小Bug改进
if(Math.abs(balla.vx-ballb.vx)<0.01&&Math.abs(balla.vy-ballb.vy)<0.01)
{
console.log(balla.vx);
balla.vx=-balla.vx;
balla.vy=-balla.vy;
return;
}
} //判断是否碰撞到画布的边缘
if(balla.x+balla.size>=width||balla.x-balla.size<=0)
{
balla.vx*=-0.98;
}
if(balla.y+balla.size>=height||balla.y-balla.size<=0)
{
balla.vy*=-0.98;
} if(ballb.x+ballb.size>=width||ballb.x-ballb.size<=0)
{
ballb.vx*=-0.98;
}
if(ballb.y+ballb.size>=height||ballb.y-ballb.size<=0)
{
ballb.vy*=-0.98;
} //清空画布,画出小球
ctx.fillStyle = "#000";
ctx.fillRect(0,0,width,height);
balla.draw(ctx);
ballb.draw(ctx);
//console.log(ballb.vy); }
function Ball(x,y,vx,vy,ax,ay,size,rou,color,ctx){
//参数传值
//x,y为坐标点 vx,vy为小球水平和垂直方向上的速度 ax,ay为加速度
//size 为大小 rou为密度 color颜色 ctx画笔
this.x = x;
this.y = y;
this.vx = vx;
this.vy = vy;
this.rou = rou;
this.size = size;
this.ax = ax;
this.ay = ay;
this.m = Math.PI*this.size*this.size*rou;//求出质量 this.draw = function(ctx){
ctx.fillStyle=color;
//console.log(this.x, this.y,this.size);
ctx.beginPath();
ctx.arc(this.x, this.y, this.size, 0, Math.PI*2,false);//画圆
ctx.fill();
ctx.closePath();
}
this.draw(ctx);
}
</script>
</html>
欢迎交流学习!!!
不定时随缘更新。