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网上看到一个释放烟花的canvas案例，很好看哦。
新建文本，把下面代码复制进去，后缀名改为html，用浏览器打开即可。
看懂注释后，可以自己修改烟花的各个效果。我试过让烟花炸成了心型。:-)
<!DOCTYPE html> <html dir="ltr" lang="zh-CN"> <head> <meta charset="UTF-8" /> <meta name="viewport" content="width=device-width" /> <title>HTML5 Canvas烟花特效 场景十分华丽在线演示</title> <style> /* basic styles for black background and crosshair cursor */ body { background: #000; margin: 0; } canvas { cursor: crosshair; display: block; } </style> </head> <body> <div style="text-align:center;clear:both"> <script src="/gg_bd_ad_720x90.js" type="text/javascript"></script> <script src="/follow.js" type="text/javascript"></script> </div> <canvas id="canvas">Canvas is not supported in your browser.</canvas> <script> // 当动画在canvas上,最好使用requestAnimationFrame代替setTimeout和setInterval // 不支持在所有的浏览器,有时需要一个前缀,所以我们需要一个重置 window.requestAnimFrame = (function () { return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || function (callback) { window.setTimeout(callback, 1000 / 60); }; })(); // 设置基本变量 var canvas = document.getElementById(‘canvas‘), ctx = canvas.getContext(‘2d‘), // 全屏幕尺寸 cw = window.innerWidth, ch = window.innerHeight, // firework collection 烟花集合 fireworks = [], // particle collection 爆炸粒子集合 particles = [], // starting hue 开始色调 hue = 120, // when launching fireworks with a click, too many get launched at once without a limiter, one launch per 5 loop ticks // 通过点击释放烟花没有限制，每5次循环释放一次 limiterTotal = 5, limiterTick = 0, // this will time the auto launches of fireworks, one launch per 80 loop ticks // 自动发射80循环一次 timerTotal = 20, timerTick = 0, mousedown = false, // mouse x coordinate X坐标 mx, // mouse y coordinate Y坐标 my; // set canvas dimensions 设置画布尺寸 canvas.width = cw; canvas.height = ch; // now we are going to setup our function placeholders for the entire demo // get a random number within a range // 获取范围内随机数 function random(min, max) { return Math.random() * (max - min) + min; } // calculate the distance between two points // 计算两点距离 function calculateDistance(p1x, p1y, p2x, p2y) { var xDistance = p1x - p2x, yDistance = p1y - p2y; return Math.sqrt(Math.pow(xDistance, 2) + Math.pow(yDistance, 2)); } // 创建烟花 function Firework(sx, sy, tx, ty) { // actual coordinates 实际坐标 this.x = sx; this.y = sy; // starting coordinates 开始坐标 this.sx = sx; this.sy = sy; // target coordinates 目标坐标 this.tx = tx; this.ty = ty; // distance from starting point to target 计算飞行距离 this.distanceToTarget = calculateDistance(sx, sy, tx, ty); this.distanceTraveled = 0; // track the past coordinates of each firework to create a trail effect, increase the coordinate count to create more prominent trails // 追踪每个烟花经过的坐标，来创建一个跟踪效果,增加坐标数量来创造更多杰出的轨迹 this.coordinates = []; this.coordinateCount = 3; // populate initial coordinate collection with the current coordinates // 填充初始坐标集合与当前坐标 while (this.coordinateCount--) { this.coordinates.push([this.x, this.y]); } this.angle = Math.atan2(ty - sy, tx - sx); // 从x轴到指定坐标点(x, y)的角度(以弧度为单位) this.speed = 2; // 速度 this.acceleration = 1.05; // 加速度 this.brightness = random(50, 70); // 亮度 // circle target indicator radius // 圆形目标指示器半径 this.targetRadius = 1; } // update firework 更新烟花 Firework.prototype.update = function (index) { // remove last item in coordinates array 删除烟花坐标数组里最后一个坐标 this.coordinates.pop(); // add current coordinates to the start of the array 当前的坐标添加到烟花坐标数组的开始 this.coordinates.unshift([this.x, this.y]); // 循环圆形目标指示器半径 if (this.targetRadius < 8) { this.targetRadius += 0.3; } else { this.targetRadius = 1; } // speed up the firework 烟花速度 this.speed *= this.acceleration; // get the current velocities based on angle and speed // 获取x,y两个方向的速度 var vx = Math.cos(this.angle) * this.speed, vy = Math.sin(this.angle) * this.speed; // how far will the firework have traveled with velocities applied? // 烟花会随速度飞行多远 this.distanceTraveled = calculateDistance(this.sx, this.sy, this.x + vx, this.y + vy); // if the distance traveled, including velocities, is greater than the initial distance to the target, then the target has been reached // 如果距离, 包括速度大于初始距离的目标, 那么目标已经达到 if (this.distanceTraveled >= this.distanceToTarget) { createParticles(this.tx, this.ty); // 创建粒子 // remove the firework, use the index passed into the update function to determine which to remove // 删除烟花,使用索引传递到更新函数来确定删除 fireworks.splice(index, 1); } else { // target not reached, keep traveling 目标没有达到,继续飞行 this.x += vx; this.y += vy; } } // draw firework 绘制烟花 Firework.prototype.draw = function () { ctx.beginPath(); // move to the last tracked coordinate in the set, then draw a line to the current x and y // 移动到最后一个跟踪坐标,然后画一条线到当前的x和y ctx.moveTo(this.coordinates[this.coordinates.length - 1][0], this.coordinates[this.coordinates.length - 1][1]); ctx.lineTo(this.x, this.y); // 色调（0或360表示红色，120表示绿色，240表示蓝色）；饱和度；亮度 ctx.strokeStyle = ‘hsl(‘ + hue + ‘, 100%, ‘ + this.brightness + ‘%)‘; ctx.stroke(); ctx.beginPath(); // draw the target for this firework with a pulsing circle // 使用圆跳动画这个烟花的目标点 ctx.arc(this.tx, this.ty, this.targetRadius, 0, Math.PI * 2); // 画圆 ctx.stroke(); } // create particle 创建爆炸粒子 function Particle(x, y) { this.x = x; this.y = y; // track the past coordinates of each particle to create a trail effect, increase the coordinate count to create more prominent trails // 追踪每个爆炸粒子经过的坐标，来创建一个跟踪效果,增加坐标数量来创造更多杰出的轨迹 this.coordinates = []; this.coordinateCount = 5; while (this.coordinateCount--) { this.coordinates.push([this.x, this.y]); } // set a random angle in all possible directions, in radians // 在所有可能的方向,设置一个随机角弧度 this.angle = random(0, Math.PI * 2); this.speed = random(1, 10); // friction will slow the particle down 摩擦会使粒子慢下来 this.friction = 0.95; // gravity will be applied and pull the particle down 重力将应用粒子拉下来 this.gravity = 2; // set the hue to a random number +-20 of the overall hue variable // 在烟花色度范围内随机取爆炸粒子色度 this.hue = random(hue - 50, hue + 50); this.brightness = random(50, 80); this.alpha = 1; // set how fast the particle fades out 设置粒子消失的速度 this.decay = random(0.015, 0.03); } // update particle 更新爆炸粒子 Particle.prototype.update = function (index) { // remove last item in coordinates array 删除爆炸粒子坐标数组里最后一个坐标 this.coordinates.pop(); // add current coordinates to the start of the array 当前的坐标添加到爆炸粒子坐标数组的开始 this.coordinates.unshift([this.x, this.y]); // slow down the particle 减缓粒子 this.speed *= this.friction; // apply velocity this.x += Math.cos(this.angle) * this.speed; this.y += Math.sin(this.angle) * this.speed + this.gravity; // fade out the particle 粒子消失参数 this.alpha -= this.decay; // remove the particle once the alpha is low enough, based on the passed in index // 删除粒子,使用索引传递到更新函数来确定删除 if (this.alpha <= this.decay) { particles.splice(index, 1); } } // draw particle 绘制爆炸粒子 Particle.prototype.draw = function () { ctx.beginPath(); // move to the last tracked coordinates in the set, then draw a line to the current x and y // 移动到最后一个坐标跟踪设置,然后画一条线到当前的x和y ctx.moveTo(this.coordinates[this.coordinates.length - 1][0], this.coordinates[this.coordinates.length - 1][1]); ctx.lineTo(this.x, this.y); // 色调（0或360表示红色，120表示绿色，240表示蓝色）；饱和度；亮度 ctx.strokeStyle = ‘hsla(‘ + this.hue + ‘, 100%, ‘ + this.brightness + ‘%, ‘ + this.alpha + ‘)‘; ctx.stroke(); } // create particle group/explosion 创建爆炸粒子组 function createParticles(x, y) { // increase the particle count for a bigger explosion, beware of the canvas performance hit with the increased particles though // 增加粒子数创造更大的爆炸,谨防增加粒子造成canvas与性能影响 var particleCount = parseInt(random(20, 50)); while (particleCount--) { particles.push(new Particle(x, y)); } } // 主循环 function loop() { // this function will run endlessly with requestAnimationFrame // 这个函数将无限运行requestAnimationFrame requestAnimFrame(loop); // increase the hue to get different colored fireworks over time // 增加颜度，随着时间的推移得到不同颜色的烟火 hue += random(0.5,10); // normally, clearRect() would be used to clear the canvas // we want to create a trailing effect though // setting the composite operation to destination-out will allow us to clear the canvas at a specific opacity, rather than wiping it entirely // 设置复合操作destination-out将使我们能够把画布清理在在一个特定的不透明度,而不是完全抹去它 ctx.globalCompositeOperation = ‘destination-out‘; // 在源图像外显示目标图像。只有源图像外的目标图像部分会被显示，源图像是透明的。 // decrease the alpha property to create more prominent trails // 降低alpha属性来创建更加显著的轨迹（0.5是透明度） ctx.fillStyle = ‘rgba(0, 0, 0, 0.5)‘; ctx.fillRect(0, 0, cw, ch); // change the composite operation back to our main mode 改变复合操作回到我们的主要模式 // lighter creates bright highlight points as the fireworks and particles overlap each other ctx.globalCompositeOperation = ‘lighter‘; // 显示源图像 + 目标图像。 // loop over each firework, draw it, update it // 循环绘制烟花 var i = fireworks.length; while (i--) { fireworks[i].draw(); fireworks[i].update(i); } // 循环绘制粒子 var i = particles.length; while (i--) { particles[i].draw(); particles[i].update(i); } // launch fireworks automatically to random coordinates, when the mouse isn‘t down // 当鼠标不点击，自动随机坐标发射烟火 if (timerTick >= timerTotal) { if (!mousedown) { var sw = random(0, cw); // start the firework at the bottom middle of the screen, then set the random target coordinates, the random y coordinates will be set within the range of the top half of the screen // 启动烟花在屏幕中间的底部, 然后设置随机目标坐标, 随机y坐标将范围内的屏幕的上半部分 fireworks.push(new Firework(sw, ch, sw, random(0, ch / 2))); timerTick = 0; } } else { timerTick++; } // limit the rate at which fireworks get launched when mouse is down // 限制鼠标点击时烟花发射的速度 if (limiterTick >= limiterTotal) { if (mousedown) { // start the firework at the bottom middle of the screen, then set the current mouse coordinates as the target // 启动烟花在屏幕中间的底部,然后将鼠标当前坐标设置为目标 fireworks.push(new Firework(mx, ch, mx, my)); limiterTick = 0; } } else { limiterTick++; } } // mouse event bindings // update the mouse coordinates on mousemove // 更新鼠标当前坐标 canvas.addEventListener(‘mousemove‘, function (e) { mx = e.pageX - canvas.offsetLeft; my = e.pageY - canvas.offsetTop; }); // toggle mousedown state and prevent canvas from being selected // 切换mousedown状态，防止canvas被选中 canvas.addEventListener(‘mousedown‘, function (e) { e.preventDefault(); mousedown = true; }); canvas.addEventListener(‘mouseup‘, function (e) { e.preventDefault(); mousedown = false; }); // 登录启动 window.onload = loop; </script> </body> </html>
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原文地址：http://www.cnblogs.com/ariter/p/5983370.html
