小编给大家分享一下JavaScript中canvas如何实现流星特效，希望大家阅读完这篇文章之后都有所收获，下面让我们一起去探讨吧！
function easeInQuad(curtime,begin,end,duration){
let x = curtime/duration; //x值
let y = x*x; //y值
return begin+(end-begin)*y; //套入最初的公式
}
//用平方根构建的缓慢减速运动 核心函数:x*x + 2*x
function easeOutQuad(curtime,begin,end,duration){
let x = curtime/duration; //x值
let y = -x*x + 2*x; //y值
return begin+(end-begin)*y; //套入最初的公式
}
function easeInoutQuad(curtime,begin,end,duration){
if(curtime<duration/2){ //前半段时间
return easeInQuad(curtime,begin,(begin+end)/2,duration/2);//改变量和时间都除以2
}else{
let curtime1 = curtime-duration/2; //注意时间要减去前半段时间
let begin1 = (begin+end)/2;//初始量要加上前半段已经完成的
return easeOutQuad(curtime1,begin1,end,duration/2);//改变量和时间都除以2
}
}function intervalOpcity (cur=0,start=0.3,end=0.8,dur=3) {
if(fadeOpcity(cur,start,end,dur)===end){
cur = 0
let temp = start
start = end
end = temp
}
let opcity = fadeOpcity(cur,start,end,dur)
let color = `rgba(0,0,0,${opcity})`
clearBgcolor(wrap)
newParticle (wrap,[x,y],r,color)
cur=parseFloat(cur+0.1)
setTimeout(()=>{intervalOpcity (cur,start,end,dur)},33)
}function intervalMove (speed,g=0) {
if(g===720){
g = 360
}
g = g+speed
let nextPosition = movePosition (a,g,startPosition)
x = nextPosition[0]
y = nextPosition[1]
clearBgcolor(wrap1)
for(let i =1;i<=360;i++){
let g1 = g-i/2
if(g1<0&&g<=360){
break
}
let g1Position = movePosition (a,g1,startPosition)
newParticle (wrap1,[g1Position[0],g1Position[1]],r/(1+i/5),`rgba(255,200,200,0.5)`)
}
setTimeout(()=>{intervalMove (speed,g)},33)
}function easeInQuad(curtime,begin,end,duration){
let x = curtime/duration; //x值
let y = x*x; //y值
return begin+(end-begin)*y; //套入最初的公式
}
//用平方根构建的缓慢减速运动 核心函数:x*x + 2*x
function easeOutQuad(curtime,begin,end,duration){
let x = curtime/duration; //x值
let y = -x*x + 2*x; //y值
return begin+(end-begin)*y; //套入最初的公式
}
function easeInoutQuad(curtime,begin,end,duration){
if(curtime<duration/2){ //前半段时间
return easeInQuad(curtime,begin,(begin+end)/2,duration/2);//改变量和时间都除以2
}else{
let curtime1 = curtime-duration/2; //注意时间要减去前半段时间
let begin1 = (begin+end)/2;//初始量要加上前半段已经完成的
return easeOutQuad(curtime1,begin1,end,duration/2);//改变量和时间都除以2
}
}
function newCanvas (width,height) {
let bodyEl = document.body
let canvasEl = document.createElement("canvas")
canvasEl.width = width
canvasEl.height = height
canvasEl.style.position = "absolute"
bodyEl.append(canvasEl)
let wrap = canvasEl.getContext("2d")
return wrap
}
function setBgcolor (wrap,color) {
wrap.fillStyle=color;
wrap.fillRect(0,0,wrap.canvas.width,wrap.canvas.height);
}
function clearBgcolor(wrap){
wrap.clearRect(0,0,wrap.canvas.width,wrap.canvas.height)
}
function newParticle (wrap,position,r,color) {
let x = position[0]
let y = position[1]
wrap.fillStyle=color;
wrap.beginPath();
wrap.arc(x,y,r,0,2*Math.PI);
wrap.shadowBlur=20;
wrap.shadowColor=`rgba(255,255,255,0.8)`;
wrap.fill();
}
function fadeOpcity(cur,start,end,dur){
let opcity = parseFloat(easeInoutQuad(cur,start,end,dur).toFixed(2))
return opcity
}
let wrap0 = newCanvas (1000,800)
let wrap2 = newCanvas (1000,800)
let wrap = newCanvas (1000,800)
let wrap1 = newCanvas (1000,800)
setBgcolor (wrap0,"black")
setBgcolor (wrap,"rgba(0,0,0,0)")
setBgcolor (wrap1,"rgba(0,0,0,0)")
setBgcolor (wrap2,"rgba(0,0,0,0)")
let startPosition = [500,200]
let r = 10
let a = -200
let x = a*(1-Math.cos(0))*Math.sin(0)+startPosition[0]
let y = a*(1-Math.cos(0))*Math.cos(0)+startPosition[1]
function movePosition (a,g,startPosition) {
let t = Math.PI*2/360
let x = a*(1-Math.cos(g*t))*Math.sin(g*t)+startPosition[0]
let y = a*(1-Math.cos(g*t))*Math.cos(g*t)+startPosition[1]
return [x,y]
}
function intervalMove (speed,g=0) {
if(g===720){
g = 360
}
g = g+speed
let nextPosition = movePosition (a,g,startPosition)
x = nextPosition[0]
y = nextPosition[1]
clearBgcolor(wrap1)
for(let i =1;i<=360;i++){
let g1 = g-i/2
if(g1<0&&g<=360){
break
}
let g1Position = movePosition (a,g1,startPosition)
newParticle (wrap1,[g1Position[0],g1Position[1]],r/(1+i/5),`rgba(255,200,200,0.5)`)
}
setTimeout(()=>{intervalMove (speed,g)},33)
}
function intervalOpcity (cur=0,start=0.3,end=0.8,dur=3) {
if(fadeOpcity(cur,start,end,dur)===end){
cur = 0
let temp = start
start = end
end = temp
}
let opcity = fadeOpcity(cur,start,end,dur)
let color = `rgba(0,0,0,${opcity})`
clearBgcolor(wrap)
newParticle (wrap,[x,y],r,color)
cur=parseFloat(cur+0.1)
setTimeout(()=>{intervalOpcity (cur,start,end,dur)},33)
}
intervalOpcity ()
intervalMove (1)1.可以使网页具有交互性，例如响应用户点击，给用户提供更好的体验。 2.可以处理表单，检验用户的输入，并提供及时反馈节省用户时间。 3.可以根据用户的操作，动态的创建页面。 4使用JavaScript可以通过设置cookie存储在浏览器上的一些临时信息。
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