Canva背景效果

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JavaScript

(function($){
	var canvas = $('#bg').children('canvas'),
		background = canvas[0],
		foreground1 = canvas[1],
		foreground2 = canvas[2],
		config = {
			circle: {
				amount: 18,
				layer: 3,
				color: [157, 97, 207],
				alpha: 0.3
			},
			line: {
				amount: 12,
				layer: 3,
				color: [255, 255, 255],
				alpha: 0.3
			},
			speed: 0.5,
			angle: 20
		};

if (background.getContext){
		var bctx = background.getContext('2d'),
			fctx1 = foreground1.getContext('2d'),
			fctx2 = foreground2.getContext('2d'),
			M = window.Math, // Cached Math
			degree = config.angle/360*M.PI*2,
			circles = [],
			lines = [],
			wWidth, wHeight, timer;
		
		requestAnimationFrame = window.requestAnimationFrame || 
			window.mozRequestAnimationFrame ||
			window.webkitRequestAnimationFrame ||
			window.msRequestAnimationFrame ||
			window.oRequestAnimationFrame ||
			function(callback, element) { setTimeout(callback, 1000 / 60); };

cancelAnimationFrame = window.cancelAnimationFrame ||
			window.mozCancelAnimationFrame ||
			window.webkitCancelAnimationFrame ||
			window.msCancelAnimationFrame ||
			window.oCancelAnimationFrame ||
			clearTimeout;

var setCanvasHeight = function(){
			wWidth = $(window).width();
			wHeight = $(window).height(),

canvas.each(function(){
				this.width = wWidth;
				this.height = wHeight;
			});
		};

var drawCircle = function(x, y, radius, color, alpha){
			var gradient = fctx1.createRadialGradient(x, y, radius, x, y, 0);
			gradient.addColorStop(0, 'rgba('+color[0]+','+color[1]+','+color[2]+','+alpha+')');
			gradient.addColorStop(1, 'rgba('+color[0]+','+color[1]+','+color[2]+','+(alpha-0.1)+')');

fctx1.beginPath();
			fctx1.arc(x, y, radius, 0, M.PI*2, true);
			fctx1.fillStyle = gradient;
			fctx1.fill();
		};

var drawLine = function(x, y, width, color, alpha){
			var endX = x+M.sin(degree)*width,
				endY = y-M.cos(degree)*width,
				gradient = fctx2.createLinearGradient(x, y, endX, endY);
			gradient.addColorStop(0, 'rgba('+color[0]+','+color[1]+','+color[2]+','+alpha+')');
			gradient.addColorStop(1, 'rgba('+color[0]+','+color[1]+','+color[2]+','+(alpha-0.1)+')');

fctx2.beginPath();
			fctx2.moveTo(x, y);
			fctx2.lineTo(endX, endY);
			fctx2.lineWidth = 3;
			fctx2.lineCap = 'round';
			fctx2.strokeStyle = gradient;
			fctx2.stroke();
		};

var drawBack = function(){
			bctx.clearRect(0, 0, wWidth, wHeight);

var gradient = [];
			
			gradient[0] = bctx.createRadialGradient(wWidth*0.3, wHeight*0.1, 0, wWidth*0.3, wHeight*0.1, wWidth*0.9);
			gradient[0].addColorStop(0, 'rgb(0, 26, 77)');
			gradient[0].addColorStop(1, 'transparent');

bctx.translate(wWidth, 0);
			bctx.scale(-1,1);
			bctx.beginPath();
			bctx.fillStyle = gradient[0];
			bctx.fillRect(0, 0, wWidth, wHeight);

gradient[1] = bctx.createRadialGradient(wWidth*0.1, wHeight*0.1, 0, wWidth*0.3, wHeight*0.1, wWidth);
			gradient[1].addColorStop(0, 'rgb(0, 150, 240)');
			gradient[1].addColorStop(0.8, 'transparent');

bctx.translate(wWidth, 0);
			bctx.scale(-1,1);
			bctx.beginPath();
			bctx.fillStyle = gradient[1];
			bctx.fillRect(0, 0, wWidth, wHeight);

gradient[2] = bctx.createRadialGradient(wWidth*0.1, wHeight*0.5, 0, wWidth*0.1, wHeight*0.5, wWidth*0.5);
			gradient[2].addColorStop(0, 'rgb(40, 20, 105)');
			gradient[2].addColorStop(1, 'transparent');

bctx.beginPath();
			bctx.fillStyle = gradient[2];
			bctx.fillRect(0, 0, wWidth, wHeight);
		};

var animate = function(){
			var sin = M.sin(degree),
				cos = M.cos(degree);

if (config.circle.amount > 0 && config.circle.layer > 0){
				fctx1.clearRect(0, 0, wWidth, wHeight);
				for (var i=0, len = circles.length; i<len; i++){
					var item = circles[i],
						x = item.x,
						y = item.y,
						radius = item.radius,
						speed = item.speed;

if (x > wWidth + radius){
						x = -radius;
					} else if (x < -radius){
						x = wWidth + radius
					} else {
						x += sin*speed;
					}

if (y > wHeight + radius){
						y = -radius;
					} else if (y < -radius){
						y = wHeight + radius;
					} else {
						y -= cos*speed;
					}

item.x = x;
					item.y = y;
					drawCircle(x, y, radius, item.color, item.alpha);
				}
			}

if (config.line.amount > 0 && config.line.layer > 0){
				fctx2.clearRect(0, 0, wWidth, wHeight);
				for (var j=0, len = lines.length; j<len; j++){
					var item = lines[j],
						x = item.x,
						y = item.y,
						width = item.width,
						speed = item.speed;

if (x > wWidth + width * sin){
						x = -width * sin;
					} else if (x < -width * sin){
						x = wWidth + width * sin;
					} else {
						x += sin*speed;
					}

if (y > wHeight + width * cos){
						y = -width * cos;
					} else if (y < -width * cos){
						y = wHeight + width * cos;
					} else {
						y -= cos*speed;
					}
					
					item.x = x;
					item.y = y;
					drawLine(x, y, width, item.color, item.alpha);
				}
			}

timer = requestAnimationFrame(animate);
		};

var createItem = function(){
			circles = [];
			lines = [];

if (config.circle.amount > 0 && config.circle.layer > 0){
				for (var i=0; i<config.circle.amount/config.circle.layer; i++){
					for (var j=0; j<config.circle.layer; j++){
						circles.push({
							x: M.random() * wWidth,
							y: M.random() * wHeight,
							radius: M.random()*(20+j*5)+(20+j*5),
							color: config.circle.color,
							alpha: M.random()*0.2+(config.circle.alpha-j*0.1),
							speed: config.speed*(1+j*0.5)
						});
					}
				}
			}

if (config.line.amount > 0 && config.line.layer > 0){
				for (var m=0; m<config.line.amount/config.line.layer; m++){
					for (var n=0; n<config.line.layer; n++){
						lines.push({
							x: M.random() * wWidth,
							y: M.random() * wHeight,
							width: M.random()*(20+n*5)+(20+n*5),
							color: config.line.color,
							alpha: M.random()*0.2+(config.line.alpha-n*0.1),
							speed: config.speed*(1+n*0.5)
						});
					}
				}
			}

cancelAnimationFrame(timer);
			timer = requestAnimationFrame(animate);
			drawBack();
		};

$(document).ready(function(){
			setCanvasHeight();
			createItem();
		});
		$(window).resize(function(){
			setCanvasHeight();
			createItem();
		});
	}
})(jQuery);

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