HTML5实现烟花绽放（支持老版浏览器）
今天来看一个利用canvas+javascript实现的烟花绽放效果，大家可以到我的codepen看看DEMO，在线观看或是下载研究，悉听尊便。
首先来看看html，里面就放了一个canvas对象。
<!-- setup our canvas element --> <canvas id="canvas">Canvas is not supported in your browser.</canvas>
css文件
body { background: #000; margin: 0; } canvas { cursor: crosshair; display: block; }
接着是JS，首先使用“RequestAnimationFrame”实现动画，可以有效解决setTimeout和setInterval的浪费CPU问题。关于RequestAnimationFrame方法的特性和优势，大家可以参考以下几篇文章。
CSS-Tricks上的《Using requestAnimationFrame》
Treehouse Blog上的《Efficient Animations with requestAnimationFrame》
W3c的候选推荐标准《Timing control for script-based animations》
以及Erik Möller提供的polyfill（在旧版浏览器上模拟标准 API 的 JavaScript 补充）。
// http://paulirish.com/2011/requestanimationframe-for-smart-animating/ // http://my.opera.com/emoller/blog/2011/12/20/requestanimationframe-for-smart-er-animating // requestAnimationFrame polyfill by Erik Möller. fixes from Paul Irish and Tino Zijdel // MIT license (function() { var lastTime = 0; var vendors = ['ms', 'moz', 'webkit', 'o']; for(var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) { window.requestAnimationFrame = window[vendors[x]+'RequestAnimationFrame']; window.cancelAnimationFrame = window[vendors[x]+'CancelAnimationFrame'] || window[vendors[x]+'CancelRequestAnimationFrame']; } if (!window.requestAnimationFrame) window.requestAnimationFrame = function(callback, element) { var currTime = new Date().getTime(); var timeToCall = Math.max(0, 16 - (currTime - lastTime)); var id = window.setTimeout(function() { callback(currTime + timeToCall); }, timeToCall); lastTime = currTime + timeToCall; return id; }; if (!window.cancelAnimationFrame) window.cancelAnimationFrame = function(id) { clearTimeout(id); }; }());
本案例需要两个类烟花沫粒子和烟花。首先来看烟花沫类
// create particle 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 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 this.angle = random( 0, Math.PI * 2 ); this.speed = random( 1, 10 ); // friction will slow the particle down this.friction = 0.95; // gravity will be applied and pull the particle down this.gravity = 1; // set the hue to a random number +-20 of the overall hue variable this.hue = random( hue - 20, hue + 20 ); this.brightness = random( 50, 80 ); this.alpha = 1; // set how fast the particle fades out this.decay = random( 0.015, 0.03 ); } // update particle Particle.prototype.update = function( index ) { // remove last item in coordinates array this.coordinates.pop(); // add current coordinates to the start of the array this.coordinates.unshift( [ this.x, this.y ] ); // slow down the particle 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 this.alpha -= this.decay; // remove the particle once the alpha is low enough, based on the passed in index if( this.alpha <= this.decay ) { particles.splice( index, 1 ); } } // draw particle 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 ctx.moveTo( this.coordinates[ this.coordinates.length - 1 ][ 0 ], this.coordinates[ this.coordinates.length - 1 ][ 1 ] ); ctx.lineTo( this.x, this.y ); ctx.strokeStyle = 'hsla(' + this.hue + ', 100%, ' + this.brightness + '%, ' + this.alpha + ')'; ctx.stroke(); }
生成粒子的函数
// create particle group/explosion function createParticles( x, y ) { // increase the particle count for a bigger explosion, beware of the canvas performance hit with the increased particles though var particleCount = 30; while( particleCount-- ) { particles.push( new Particle( x, y ) ); } }
烟花类
// create firework function Firework( sx, sy, tx, ty ) { // actual coordinates this.x = sx; this.y = sy; // starting coordinates this.sx = sx; this.sy = sy; // target coordinates this.tx = tx; this.ty = ty; // distance from starting point to target 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 this.coordinates = []; this.coordinateCount = 3; // populate initial coordinate collection with the current coordinates while( this.coordinateCount-- ) { this.coordinates.push( [ this.x, this.y ] ); } this.angle = Math.atan2( ty - sy, tx - sx ); this.speed = 2; this.acceleration = 1.05; this.brightness = random( 50, 70 ); // circle target indicator radius this.targetRadius = 1; } // update firework Firework.prototype.update = function( index ) { // remove last item in coordinates array this.coordinates.pop(); // add current coordinates to the start of the array this.coordinates.unshift( [ this.x, this.y ] ); // cycle the circle target indicator radius if( this.targetRadius < 8 ) { this.targetRadius += 0.3; } else { this.targetRadius = 1; } // speed up the firework this.speed *= this.acceleration; // get the current velocities based on angle and speed 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? 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 if( this.distanceTraveled >= this.distanceToTarget ) { createParticles( this.tx, this.ty ); // remove the firework, use the index passed into the update function to determine which to remove fireworks.splice( index, 1 ); } else { // target not reached, keep traveling this.x += vx; this.y += vy; } } // draw firework 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 ctx.moveTo( this.coordinates[ this.coordinates.length - 1][ 0 ], this.coordinates[ this.coordinates.length - 1][ 1 ] ); ctx.lineTo( this.x, this.y ); ctx.strokeStyle = 'hsl(' + hue + ', 100%, ' + this.brightness + '%)'; ctx.stroke(); ctx.beginPath(); // draw the target for this firework with a pulsing circle ctx.arc( this.tx, this.ty, this.targetRadius, 0, Math.PI * 2 ); ctx.stroke(); }
定义好了主要的类，我们来设置一些常见的变量和函数。
// now we will setup our basic variables for the demo var canvas = document.getElementById( 'canvas' ), ctx = canvas.getContext( '2d' ), // full screen dimensions cw = window.innerWidth, ch = window.innerHeight, // firework collection fireworks = [], // particle collection particles = [], // starting hue hue = 120, // when launching fireworks with a click, too many get launched at once without a limiter, one launch per 5 loop ticks limiterTotal = 5, limiterTick = 0, // this will time the auto launches of fireworks, one launch per 80 loop ticks timerTotal = 80, timerTick = 0, mousedown = false, // mouse x coordinate, mx, // mouse y coordinate my; // set canvas dimensions 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 function random( min, max ) { return Math.random() * ( max - min ) + min; } // calculate the distance between two points function calculateDistance( p1x, p1y, p2x, p2y ) { var xDistance = p1x - p2x, yDistance = p1y - p2y; return Math.sqrt( Math.pow( xDistance, 2 ) + Math.pow( yDistance, 2 ) ); }
不断释放烟花的函数，需要利用RequestAnimationFrame不断地执行函数。
// main demo loop function loop() { // this function will run endlessly with requestAnimationFrame requestAnimFrame( loop ); // increase the hue to get different colored fireworks over time hue += 0.5; // 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 ctx.globalCompositeOperation = 'destination-out'; // decrease the alpha property to create more prominent trails ctx.fillStyle = 'rgba(0, 0, 0, 0.5)'; ctx.fillRect( 0, 0, cw, ch ); // change the composite operation back to our main mode // lighter creates bright highlight points as the fireworks and particles overlap each other ctx.globalCompositeOperation = 'lighter'; // loop over each firework, draw it, update it var i = fireworks.length; while( i-- ) { fireworks[ i ].draw(); fireworks[ i ].update( i ); } // loop over each particle, draw it, update it 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 if( timerTick >= timerTotal ) { if( !mousedown ) { // 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 fireworks.push( new Firework( cw / 2, ch, random( 0, cw ), random( 0, ch / 2 ) ) ); timerTick = 0; } } else { timerTick++; } // limit the rate at which fireworks get launched when mouse is down if( limiterTick >= limiterTotal ) { if( mousedown ) { // start the firework at the bottom middle of the screen, then set the current mouse coordinates as the target fireworks.push( new Firework( cw / 2, ch, mx, my ) ); limiterTick = 0; } } else { limiterTick++; } }
绑定鼠标事件
// mouse event bindings // update the mouse coordinates on mousemove canvas.addEventListener( 'mousemove', function( e ) { mx = e.pageX - canvas.offsetLeft; my = e.pageY - canvas.offsetTop; }); // toggle mousedown state and prevent canvas from being selected canvas.addEventListener( 'mousedown', function( e ) { e.preventDefault(); mousedown = true; }); canvas.addEventListener( 'mouseup', function( e ) { e.preventDefault(); mousedown = false; });
在窗口加载完毕，单击鼠标前，我们也需要一些烟花
// once the window loads, we are ready for some fireworks! window.onload = loop;
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转自：https://software.intel.com/zh-cn/blogs/2014/02/28/html5/?utm_campaign=CSDN&utm_source=intel.csdn.net&utm_medium=Link&utm_content=others-html5
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