技术揭秘
在HTML5中，<canvas>元素为我们提供了一个强大的绘图平台，允许我们通过JavaScript进行绘画。烟花表演，本质上就是这种绘图技术的运用。以下是实现烟花效果的简要步骤：
初始化画布：设置画布尺寸，确保画布能够适应不同的屏幕大小。
定义烟花行为：通过编写JavaScript函数来定义烟花的运动轨迹、颜色和消失方式。
绘制烟花：使用路径（Path）和填充（fill）命令在画布上绘制圆形，模拟烟花的爆炸效果。
动画循环：通过requestAnimationFrame实现动画循环，不断地更新和重绘烟花的位置和状态。
1、创建一个 index.html 复制以下代码
<!DOCTYPE html>
<html lang=”en”>
<head>
<meta charset=”UTF-8″>
<meta name=”viewport” content=”width=device-width, initial-scale=1.0″>
<title>烟花</title>
</head>
<style>
body {
margin: 0;
padding: 0;
overflow: hidden;
}
.canvasBox {
width: 100%;
height: 100%;
display: flex;
justify-content: center;
align-items: center;
}
canvas {
border: 1px solid;
background-color: #000;
}
</style>
<body>
<div class=”canvasBox”>
<canvas id=”canvas”></canvas>
</div>
</body>
</html>
<script src=”./index.js”></script>
<script>
const canvas = document.getElementById(‘canvas’)
const canvasWidth = document.documentElement.clientWidth || document.body.clientWidth
const canvasHeight = document.documentElement.clientHeight || document.body.clientHeight
const ratio = Math.max(window.devicePixelRatio, 2)
canvas.width = canvasWidth * ratio
canvas.height = canvasHeight * ratio
canvas.style.width = canvasWidth + ‘px’
canvas.style.height = canvasHeight + ‘px’
const ctx = canvas.getContext(‘2d’)
ctx.scale(ratio, ratio)
const getRandom = (min, max) => {
return Math.random() * (max – min) + min
}
const drawCircle = ({ opacity = 1, x, y, radius, color }) => {
ctx.save()
ctx.globalAlpha = opacity
ctx.beginPath()
ctx.arc(x, y, radius, 0, Math.PI * 2)
ctx.fillStyle = color
ctx.fill()
ctx.restore()
}
const deleteFromList = (list, target) => {
const index = list.findIndex(item => {
return item === target
})
list.splice(index, 1)
}
// 动画循环
// 烟花列表
const fireworkList = []
const draw = () => {
// 使用半透明清空画布，形成拖尾效果
ctx.fillStyle = ‘rgba(0,0,0,0.3)’
ctx.fillRect(0, 0, canvasWidth, canvasHeight)
ctx.save()
// 修改坐标系
ctx.translate(0, canvasHeight)
ctx.scale(1, -1)
const list = […fireworkList]
list.forEach(firework => {
firework.update()
if (firework.isEnd()) {
deleteFromList(fireworkList, firework)
}
})
ctx.restore()
requestAnimationFrame(draw)
}
draw()
// 烟花颜色列表
const createFireworkColor = () => {
const colorList = [
‘#ff0043’,
‘#14fc56’,
‘#1e7fff’,
‘#e60aff’,
‘#ffbf36’,
‘#ffffff’
]
return colorList[Math.floor(Math.random() * colorList.length)]
}
// 发射烟花
canvas.addEventListener(‘click’, () => {
const firework = new Firework(
{
color: createFireworkColor()
})
fireworkList.push(firework)
firework.launch()
})
</script>
2、创建一个 index.js 复制以下代码
// 爆炸碎片类
class ExplosiveDebris {
constructor(opt) {
this.firework = opt.firework
this.x = opt.x
this.y = opt.y
this.color = Math.random() > 0.2 ? opt.color : ‘#fff’
this.radius = opt.radius || 2
this.angle = getRandom(0, 2 * Math.PI)
this.speed = opt.speed || getRandom(0.1, 4)
this.vx = Math.cos(this.angle) * this.speed
this.vy = Math.sin(this.angle) * this.speed
this.g = opt.g || 0.98
this.time = getRandom(0.5, 1)
this.startTime = 0
// 痕迹碎片数量
this.debrisCount = opt.debrisCount || 3
// 是否要进行二次爆炸
this.secondBurst = opt.secondBurst || false
}
start() {
this.startTime = Date.now()
}
update() {
const duration = (Date.now() – this.startTime) / 1000
const vy = this.vy – this.g * duration
this.x += this.vx
this.y += vy
const progress = duration / this.time
let opacity = progress > 0.7 ? 1 – 1 * progress : 1
if (opacity < 0) opacity = 0
drawCircle({
x: this.x,
y: this.y,
color: this.color,
radius: this.radius,
opacity: opacity
})
// 添加痕迹碎片
if (this.debrisCount > 0 && Math.random() > 0.8) {
this.debrisCount–
this.firework.addDebris({
x: this.x + getRandom(-2, 2),
y: this.y + getRandom(-2, 2),
color: this.color,
radius: 0.5,
g: 0.1
})
}
return {
x: this.x,
y: this.y,
isEnd: progress >= 1
}
}
}
// 爆炸器类
class Explosive {
constructor(opt) {
this.firework = opt.firework
this.x = opt.x
this.y = opt.y
this.color = opt.color
// 爆炸碎片列表
this.debrisList = []
// 爆炸碎片数量
this.debrisNum = opt.debrisNum || getRandom(50, 400)
// 是否要二次爆炸
this.secondBurst = opt.secondBurst || this.debrisNum <= 100
//是否是第一次爆炸
this.isFirstBurst = true
}
start(debrisNum, opt = {}) {
const num = debrisNum || this.debrisNum
opt.x = opt.x || this.x
opt.y = opt.y || this.y
opt.secondBurst = this.secondBurst && this.isFirstBurst
for (let i = 0; i < num; i++) {
const explosiveDebris = new ExplosiveDebris({
firework: this.firework,
color: this.color,
…opt
})
explosiveDebris.start()
this.debrisList.push(explosiveDebris)
}
this.isFirstBurst = false
}
update() {
const list = […this.debrisList]
list.forEach(debris => {
const res = debris.update()
if (res.isEnd) {
deleteFromList(this.debrisList, debris)
// 二次爆炸
if (debris.secondBurst) {
this.start(5, {
x: res.x,
y: res.y,
speed: 1
})
}
}
})
return {
isEnd: list.length <= 0
}
}
}
// 痕迹碎片类
class Debris {
constructor(opt = {}) {
// 颜色
this.color = opt.color || ‘#fff’
// 透明度
this.opacity = getRandom(0.1, 0.5)
// 半径
this.radius = opt.radius || 1
// 存在时间
this.time = getRandom(0.5, 1)
// 重力，px/s2
this.g = opt.g || 0.98
// 位置
this.x = opt.x
this.y = opt.y
// 创建的时间
this.startTime = 0
}
start() {
this.startTime = Date.now()
}
update() {
const duration = (Date.now() – this.startTime) / 1000
this.y -= this.g * duration
drawCircle({
opacity: this.opacity,
x: this.x,
y: this.y,
radius: this.radius,
color: this.color
})
return {
x: this.x,
y: this.y,
isEnd: duration > this.time
}
}
}
// 发射器类
class Launcher {
constructor(opt = {}) {
// 烟花实例
this.firework = opt.firework
// 颜色
this.color = opt.color
// 初始位置
this.x = opt.x || canvasWidth * getRandom(0.2, 0.8)
this.y = opt.y || 0
// 目标位置
this.ty = canvasHeight * getRandom(0.6, 0.8)
// 半径
this.radius = opt.radius || getRandom(2, 5)
// 发射的持续时间
this.duration = opt.duration || getRandom(2000, 3500)
// 发射时的时间
this.startTime = 0
}
start() {
this.startTime = Date.now()
}
easeOutCubic(t, b, c, d) {
return c * ((t = t / d – 1) * t * t + 1) + b
}
update() {
const x = this.x
let y = this.easeOutCubic(
Date.now() – this.startTime,
this.y,
this.ty – this.y,
this.duration
)
y = Math.min(y, this.ty)
// 透明度变小
let opacity = 1 – 1 * (y / this.ty)
if (opacity < 0) opacity = 0
this.draw(x, y, opacity)
// 添加痕迹碎片
if (Math.random() > 0.7 && opacity >= 0.1) {
this.firework.addDebris({
x: x + getRandom(-2, 2), // x坐标添加一段随机量
y
})
}
return {
x,
y,
isEnd: y >= this.ty //返回true代表发射结束
}
}
draw(x, y, opacity) {
// 外圆，烟花的颜色
drawCircle({
opacity: opacity,
x: x,
y: y,
radius: this.radius,
color: this.color
})
// 内圆，白色
drawCircle({
opacity: opacity,
x: x,
y: y,
radius: this.radius / 2,
color: ‘#fff’
})
}
}
// 烟花类
class Firework {
constructor(opt = {}) {
// 颜色
this.color = opt.color || tinycolor.random().toHexString()
// 发射器
this.launcher = null
// 爆炸器
this.explosive = null
// 烟花状态：waiting（等待发射）、launching（发射中）、bursting（爆炸中）、end（烟花结束）
this.status = ‘waiting’
// 痕迹碎片列表
this.debrisList = []
}
// 发射
launch() {
this.launcher = new Launcher({
firework: this,
color: this.color
})
this.launcher.start()
this.status = ‘launching’
}
// 爆炸
burst({ x, y }) {
this.explosive = new Explosive({
firework: this,
x,
y,
color: this.color
})
this.explosive.start()
}
// 更新
update() {
if (this.status === ‘launching’) {
const res = this.launcher.update()
if (res.isEnd) {
this.status = ‘bursting’
this.burst(res)
}
} else if (this.status === ‘bursting’) {
const res = this.explosive.update()
if (res.isEnd) {
this.status = ‘end’
}
}
// 更新痕迹碎片
this.updateDebris()
}
// 添加痕迹碎片
addDebris(opt = {}) {
const debris = new Debris({
…opt,
color: opt.color || this.color
})
debris.start()
this.debrisList.push(debris)
}
// 更新痕迹碎片
updateDebris() {
const list = […this.debrisList]
list.forEach(debris => {
const res = debris.update()
if (res.isEnd) {
deleteFromList(this.debrisList, debris)
}
})
}
isEnd() {
return this.status === ‘end’
}
}
3、给自己放个烟花秀吧
创建一个文件夹，将以上两个文件 index.html & index.js 放到创建的文件夹中
在电脑端双击打开 index.html，即可在浏览器中打开页面，点击屏幕给自己放个烟花秀吧
！！！
