html5烟花绽放效果

叁歲伎倆 2022-08-25 08:24 229阅读 0赞

前端开发whqet,csdn,王海庆,whqet,前端开发专家

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][Link 1]或是[下载研究][Link 2]，悉听尊便。

![1420791862_3128.gif][]

首先来看看html，里面就放了一个canvas对象。

<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;

完毕。

\---------------------------------------------------------------

[前端开发whqet][whqet]，关注web前端开发技术，分享网页相关资源。  
\---------------------------------------------------------------

[Link 1]: http://codepen.io/whqet/pen/Auzch
[Link 2]: http://codepen.io/whqet/share/zip/Auzch
[1420791862_3128.gif]: https://img-my.csdn.net/uploads/201501/09/1420791862_3128.gif
[Using requestAnimationFrame]: http://css-tricks.com/using-requestanimationframe/
[Efficient Animations with requestAnimationFrame]: http://blog.teamtreehouse.com/efficient-animations-with-requestanimationframe
[Timing control for script-based animations]: http://www.w3.org/TR/animation-timing/
[polyfill]: https://gist.github.com/paulirish/1579671
[whqet]: http://blog.csdn.net/whqet