特效描述：利用HTML5实现 Canvas 空中闪电 动画特效。利用HTML5实现Canvas空中闪电动画特效

代码结构

1. 引入JS

2. HTML代码

/*=============================================================================*/

/* Canvas Lightning v1

/*=============================================================================*/

var canvasLightning = function(c, cw, ch){

/*=============================================================================*/

/* Initialize

/*=============================================================================*/

this.init = function(){

this.loop();

};

/*=============================================================================*/

/* Variables

/*=============================================================================*/

var _this = this;

this.c = c;

this.ctx = c.getContext('2d');

this.cw = cw;

this.ch = ch;

this.mx = 0;

this.my = 0;

this.lightning = [];

this.lightTimeCurrent = 0;

this.lightTimeTotal = 50;

/*=============================================================================*/

/* Utility Functions

/*=============================================================================*/

this.rand = function(rMi, rMa){return ~~((Math.random()*(rMa-rMi+1))+rMi);};

this.hitTest = function(x1, y1, w1, h1, x2, y2, w2, h2){return !(x1 + w1 < x2 || x2 + w2 < x1 || y1 + h1 < y2 || y2 + h2 < y1);};

/*=============================================================================*/

/* Create Lightning

/*=============================================================================*/

this.createL= function(x, y, canSpawn){

this.lightning.push({

x: x,

y: y,

xRange: this.rand(5, 30),

yRange: this.rand(5, 25),

path: [{

x: x,

y: y

}],

pathLimit: this.rand(10, 35),

canSpawn: canSpawn,

hasFired: false

});

};

/*=============================================================================*/

/* Update Lightning

/*=============================================================================*/

this.updateL = function(){

var i = this.lightning.length;

while(i--){

var light = this.lightning[i];

light.path.push({

x: light.path[light.path.length-1].x + (this.rand(0, light.xRange)-(light.xRange/2)),

y: light.path[light.path.length-1].y + (this.rand(0, light.yRange))

});

if(light.path.length > light.pathLimit){

this.lightning.splice(i, 1)

}

light.hasFired = true;

};

};

/*=============================================================================*/

/* Render Lightning

/*=============================================================================*/

this.renderL = function(){

var i = this.lightning.length;

while(i--){

var light = this.lightning[i];

this.ctx.strokeStyle = 'hsla(0, 100%, 100%, '+this.rand(10, 100)/100+')';

this.ctx.lineWidth = 1;

if(this.rand(0, 30) == 0){

this.ctx.lineWidth = 2;

}

if(this.rand(0, 60) == 0){

this.ctx.lineWidth = 3;

}

if(this.rand(0, 90) == 0){

this.ctx.lineWidth = 4;

}

if(this.rand(0, 120) == 0){

this.ctx.lineWidth = 5;

}

if(this.rand(0, 150) == 0){

this.ctx.lineWidth = 6;

}

this.ctx.beginPath();

var pathCount = light.path.length;

this.ctx.moveTo(light.x, light.y);

for(var pc = 0; pc < pathCount; pc++){

this.ctx.lineTo(light.path[pc].x, light.path[pc].y);

if(light.canSpawn){

if(this.rand(0, 100) == 0){

light.canSpawn = false;

this.createL(light.path[pc].x, light.path[pc].y, false);

}

}

}

if(!light.hasFired){

this.ctx.fillStyle = 'rgba(255, 255, 255, '+this.rand(4, 12)/100+')';

this.ctx.fillRect(0, 0, this.cw, this.ch);

}

if(this.rand(0, 30) == 0){

this.ctx.fillStyle = 'rgba(255, 255, 255, '+this.rand(1, 3)/100+')';

this.ctx.fillRect(0, 0, this.cw, this.ch);

}

this.ctx.stroke();

};

};

/*=============================================================================*/

/* Lightning Timer

/*=============================================================================*/

this.lightningTimer = function(){

this.lightTimeCurrent++;

if(this.lightTimeCurrent >= this.lightTimeTotal){

var newX = this.rand(100, cw - 100);

var newY = this.rand(0, ch / 2);

var createCount = this.rand(1, 3);

while(createCount--){

this.createL(newX, newY, true);

}

this.lightTimeCurrent = 0;

this.lightTimeTotal = this.rand(30, 100);

}

}

/*=============================================================================*/

/* Clear Canvas

/*=============================================================================*/

this.clearCanvas = function(){

this.ctx.globalCompositeOperation = 'destination-out';

this.ctx.fillStyle = 'rgba(0,0,0,'+this.rand(1, 30)/100+')';

this.ctx.fillRect(0,0,this.cw,this.ch);

this.ctx.globalCompositeOperation = 'source-over';

};

/*=============================================================================*/

/* Resize on Canvas on Window Resize

/*=============================================================================*/

$(window).on('resize', function(){

_this.cw = _this.c.width = window.innerWidth;

_this.ch = _this.c.height = window.innerHeight;

});

/*=============================================================================*/

/* Animation Loop

/*=============================================================================*/

this.loop = function(){

var loopIt = function(){

requestAnimationFrame(loopIt, _this.c);

_this.clearCanvas();

_this.updateL();

_this.lightningTimer();

_this.renderL();

};

loopIt();

};

};

/*=============================================================================*/

/* Check Canvas Support

/*=============================================================================*/

var isCanvasSupported = function(){

var elem = document.createElement('canvas');

return !!(elem.getContext && elem.getContext('2d'));

};

/*=============================================================================*/

/* Setup requestAnimationFrame

/*=============================================================================*/

var setupRAF = 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);

};

};

};

/*=============================================================================*/

/* Define Canvas and Initialize

/*=============================================================================*/

$(window).load(function(){

if(isCanvasSupported){

var c = document.getElementById('canvas');

var cw = c.width = window.innerWidth;

var ch = c.height = window.innerHeight;

var cl = new canvasLightning(c, cw, ch);

setupRAF();

cl.init();

}

});