javascript线性渐变三_javascript技巧

IE还有一个利器至今没有被使用过，那就是VML。虽然比不上SVG，但它还是非常强大的。在实现渐变上，其fill还比IE的Gragient滤镜强悍得多了。不过VML出现得比较早，只支持很少的颜色名，如red,blue,yellow，其他如orange就可以搞死它了。因此要使用VML做线性渐变，我们得对这些颜色名做一下转换。
HTML4的颜色值

black = #000000	green = #008000	silver = #c0c0c0	lime = #00ff00
gray = #808080	olive = #808000	white = #ffffff	yellow = #ffff00
maroon = #800000	navy = #000080	red = #ff0000	blue = #0000ff
purple = #800080	teal = #008080	fuchsia = #ff00ff	aqua = #00ffff

我们可以在火狐官网以及W3C了解到更多的颜色值。

代码如下:

 
var htmlcolor={ black :"#000",green :"#008000",silver :"#c0c0c0",lime :"#0f0", 
gray :"#808080",olive :"#808000",white :"#fff",yellow :"#ff0", 
maroon :"#800000",navy :"#000080",red :"#f00",blue :"#00f", 
purple :"#800080",teal :"#008080",fuchsia :"#f0f",aqua :"#0ff", 
indigo :"#4b0082",orange : "#ffa500",sienna :"#a0522d",plum :"#dda0dd", 
gold :"#ffd700", tan :"#d2b48c", snow :"#fffafa",violet :"#ee82ee" 
} 

接着我们在需要线性渐变的那个元素内部创建一个同样大小的rect元素，然后里面再添加一个fill元素，用来设置渐变。伪码如下：

代码如下:

javascript线性渐变 by 司徒正美实现多重水平渐变效果

<!doctype html> 
<title>javascript线性渐变 by 司徒正美</title> 
<meta charset="utf-8"/> 
<meta name="keywords" content="javascript线性渐变 by 司徒正美" /> 
<meta name="description" content="javascript线性渐变 by 司徒正美" /> 
<style type="text/css"> 
.gradient{ 
width:800px; 
height:100px; 
} 
</style> 
<script type="text/javascript"> 
var Gradient = function(id){ 
var entity = document.getElementById(id), 
options = arguments[1] || {}, 
width = options.width, 
height = options.height, 
type = options.type , 
stops = options["color-stop"]; 
this.init(entity,stops,width,height,type); 
} 
Gradient.prototype ={ 
constructor: Gradient, 
init: function(entity,stops,width,height,type) { 
this.css(entity,{position:"relative"}); 
var content = entity.innerHTML; 
entity.innerHTML = ""; 
!+"\v1"? this.IEgradient(entity,stops,width,height,type): 
this.SVGgradient(entity,stops,width,height,type) 
var contentDiv = document.createElement("div"); 
this.css(contentDiv,{position:"absolute",top:0,left:0}) 
contentDiv.innerHTML = content; 
entity.appendChild(contentDiv); 
}, 
css: function(node,bag){ 
var str = ";" 
for(var i in bag){ 
if(bag.hasOwnProperty(i)) 
str += i == "opacity" ? ("filter:alpha(opacity="+ bag[i] * 100+");"):(i+":"+bag[i]+";") 
} 
node.style.cssText = str; 
}, 
attr: function(node,bag){ 
for(var i in bag){ 
if(bag.hasOwnProperty(i)) 
node.setAttribute(i,bag[i]) 
} 
}, 
createSVG:function(tag){ 
return document.createElementNS("http://www.w3.org/2000/svg",tag); 
}, 
IEgradient:function(entity,stops,width,height,type){ 
if(!document.namespaces.vml){ 
document.namespaces.add('vml', 'urn:schemas-microsoft-com:vml'); 
var vmlobj = document.createElement("<object classid=CLSID:10072CEC-8CC1-11D1-986E-00A0C955B42E id=VMLRender>"), 
head = document.getElementsByTagName("head")[0]; 
head.appendChild(vmlobj) 
document.createStyleSheet().addRule(".vml", "behavior: url(#VMLRender); display:inline-block;"); 
} 
var rect = document.createElement('<vml:rect class="vml">'); 
entity.appendChild(rect); 
this.css(rect,{width:width+"px",height:height+"px"}); 
this.attr(rect,{stroked:"f"}); 
var fill = document.createElement('<vml:fill class="vml">'); 
var colors =""; 
for(var i=0,l=stops.length;i<l;i++){ 
var offset = stops[i].split(",")[0] + "%", 
color = this.hex(stops[i].split(",")[1]); 
colors += offset +" "+color +","; 
} 
rect.appendChild(fill); 
var angle = type ? 90 : 0; 
this.attr(fill,{type:"gradient",colors:colors,method:"sigma",focus:"100%",angle:angle}); 
}, 
SVGgradient:function(entity,stops,width,height,type){ 
var svg = this.createSVG("svg"), 
id = "id" + (new Date().getTime()* Math.random()).toFixed(0); 
this.attr(svg,{width:width+"px",height:height+"px"}) 
entity.appendChild(svg); 
var defs = this.createSVG("defs"); 
svg.appendChild(defs); 
var linearGradient = this.createSVG("linearGradient"); 
defs.appendChild(linearGradient); 
this.attr(linearGradient,{id:id,x1:"0%",y1:"0%"}) 
if(type){ 
this.attr(linearGradient,{x2:"100%",y2:"0%"}) 
}else{ 
this.attr(linearGradient,{x2:"0%",y2:"100%"}) 
} 
for(var i=0,l=stops.length;i<l;i++){ 
var offset = stops[i].split(",")[0] + "%", 
color = this.hex(stops[i].split(",")[1]), 
stop = this.createSVG("stop"); 
this.attr(stop,{offset:offset,"stop-color":color}); 
linearGradient.appendChild(stop); 
} 
var rect = this.createSVG("rect"); 
svg.appendChild(rect); 
this.attr(rect,{x:"0px",y:"0px",width:width+"px",height:height+"px", 
fill:"url(#"+linearGradient.getAttribute("id")+")"}); 
}, 
hex:function(value){ 
var color={ black :"#000",green :"#008000",silver :"#c0c0c0",lime :"#0f0", 
gray :"#808080",olive :"#808000",white :"#fff",yellow :"#ff0", 
maroon :"#800000",navy :"#000080",red :"#f00",blue :"#00f", 
purple :"#800080",teal :"#008080",fuchsia :"#f0f",aqua :"#0ff", 
indigo :"#4b0082",orange :"#ffa500",sienna :"#a0522d",plum :"#dda0dd", 
gold :"#ffd700", tan :"#d2b48c", snow :"#fffafa",violet :"#ee82ee" 
} 
if(!!color[value]){ 
value = color[value] 
} 
if(/^#/.test(value)){ 
value = value.replace('#', ''); 
return "#" + (value.length == 3 ? value.replace(/^(\w)(\w)(\w)$/, '$1$1$2$2$3$3') : value); 
} 
return value; 
} 
} 
window.onload = function(){ 
new Gradient("text1",{width:800,height:100,type:1,"color-stop":["0,red","16,orange","32,yellow","48,green","64,blue","80,indigo","100,violet"]}) 
new Gradient("text2",{width:800,height:100,type:0,"color-stop":["0,red","16,orange","32,yellow","48,green","64,blue","80,indigo","100,violet"]}) 
} 
</ script> 
<div id="text1" class="gradient">javascript线性渐变 by 司徒正美 实现多重水平渐变效果</div>

<div id="text2" class="gradient">javascript线性渐变 by 司徒正美 实现多重垂直渐变效果</div>

[Ctrl+A 全选注:如需引入外部Js需刷新才能执行]

利用VML实现IE的线性渐变后整个类的长度减少一半。
我们再来看如何实现角度渐变，IE那边好办，直接传入一个角就行了（0—360，也可以为负数）。SVG比较麻烦，它由linearGradient 的四个属性来控制倾斜度，x1,x2,y2,y2，实质就是两个点。假设第一个点为(0,0)，第二个点为（100,0），它就是水平渐变。假设第一个点为(0,0)，第二个点为（0,100），它就是垂直渐变。要实现倾斜就必须让第二个点的坐标与第一个点的坐标完全不相等，无论是X轴还是Y轴。这就要用到三角函数了。

代码如下:

 
var x = (Math.sin(angle*Math.PI/180) * 100).toFixed(2)+"%"; 
var y = (Math.cos(angle*Math.PI/180)* 100).toFixed(2)+"%"; 
this.attr(linearGradient,{x2:x,y2:y}); 

我们也应该看得出水平渐变与垂直渐变其实只是一个特例，我们大可以废除type这个属性，改成angle，传入一个0至360的数。

<!doctype html> 
<title>javascript线性渐变 by 司徒正美</title> 
<meta charset="utf-8"/> 
<meta name="keywords" content="javascript线性渐变 by 司徒正美" /> 
<meta name="description" content="javascript线性渐变 by 司徒正美" /> 
<style type="text/css"> 
.gradient{ 
width:800px; 
height:100px; 
} 
</style> 
<script type="text/javascript"> 
var Gradient = function(id){ 
var entity = document.getElementById(id), 
options = arguments[1] || {}, 
width = options.width, 
height = options.height, 
angle = options.angle , 
stops = options["color-stop"]; 
this.init(entity,stops,width,height,angle); 
} 
Gradient.prototype ={ 
constructor: Gradient, 
init: function(entity,stops,width,height,angle) { 
this.css(entity,{position:"relative"}); 
var content = entity.innerHTML; 
entity.innerHTML = ""; 
!+"\v1"? this.IEgradient(entity,stops,width,height,angle): 
this.SVGgradient(entity,stops,width,height,angle) 
var contentDiv = document.createElement("div"); 
this.css(contentDiv,{position:"absolute",top:0,left:0}) 
contentDiv.innerHTML = content; 
entity.appendChild(contentDiv); 
}, 
css: function(node,bag){ 
var str = ";" 
for(var i in bag){ 
if(bag.hasOwnProperty(i)) 
str += i == "opacity" ? ("filter:alpha(opacity="+ bag[i] * 100+");"):(i+":"+bag[i]+";") 
} 
node.style.cssText = str; 
}, 
attr: function(node,bag){ 
for(var i in bag){ 
if(bag.hasOwnProperty(i)) 
node.setAttribute(i,bag[i]) 
} 
}, 
createSVG:function(tag){ 
return document.createElementNS("http://www.w3.org/2000/svg",tag); 
}, 
IEgradient:function(entity,stops,width,height,angle){ 
if(!document.namespaces.vml){ 
document.namespaces.add('vml', 'urn:schemas-microsoft-com:vml'); 
var vmlobj = document.createElement("<object classid=CLSID:10072CEC-8CC1-11D1-986E-00A0C955B42E id=VMLRender>"), 
head = document.getElementsByTagName("head")[0]; 
head.appendChild(vmlobj) 
document.createStyleSheet().addRule(".vml", "behavior: url(#VMLRender); display:inline-block;"); 
} 
var rect = document.createElement('<vml:rect class="vml">'); 
entity.appendChild(rect); 
this.css(rect,{width:width+"px",height:height+"px"}); 
this.attr(rect,{stroked:"f"}); 
var fill = document.createElement('<vml:fill class="vml">'); 
var colors =""; 
for(var i=0,l=stops.length;i<l;i++){ 
var offset = stops[i].split(",")[0] + "%", 
color = this.hex(stops[i].split(",")[1]); 
colors += offset +" "+color +","; 
} 
rect.appendChild(fill); 
this.attr(fill,{type:"gradient",colors:colors,method:"sigma",focus:"100%",angle:angle}); 
}, 
SVGgradient:function(entity,stops,width,height,angle){ 
var svg = this.createSVG("svg"), 
id = "id" + (new Date().getTime()* Math.random()).toFixed(0); 
this.attr(svg,{width:width+"px",height:height+"px"}) 
entity.appendChild(svg); 
var defs = this.createSVG("defs"); 
svg.appendChild(defs); 
var linearGradient = this.createSVG("linearGradient"); 
defs.appendChild(linearGradient); 
this.attr(linearGradient,{id:id,x1:"0%",y1:"0%"}) 
var x = (Math.sin(angle*Math.PI/180) * 100).toFixed(2)+"%"; 
var y = (Math.cos(angle*Math.PI/180)* 100).toFixed(2)+"%"; 
this.attr(linearGradient,{x2:x,y2:y}); 
for(var i=0,l=stops.length;i<l;i++){ 
var offset = stops[i].split(",")[0] + "%", 
color = this.hex(stops[i].split(",")[1]), 
stop = this.createSVG("stop"); 
this.attr(stop,{offset:offset,"stop-color":color}); 
linearGradient.appendChild(stop); 
} 
var rect = this.createSVG("rect"); 
svg.appendChild(rect); 
this.attr(rect,{x:"0px",y:"0px",width:width+"px",height:height+"px", 
fill:"url(#"+linearGradient.getAttribute("id")+")"}); 
}, 
hex:function(value){ 
var color={ black :"#000",green :"#008000",silver :"#c0c0c0",lime :"#0f0", 
gray :"#808080",olive :"#808000",white :"#fff",yellow :"#ff0", 
maroon :"#800000",navy :"#000080",red :"#f00",blue :"#00f", 
purple :"#800080",teal :"#008080",fuchsia :"#f0f",aqua :"#0ff", 
indigo :"#4b0082",orange :"#ffa500",sienna :"#a0522d",plum :"#dda0dd", 
gold :"#ffd700", tan :"#d2b48c", snow :"#fffafa",violet :"#ee82ee" 
} 
if(!!color[value]){ 
value = color[value] 
} 
if(/^#/.test(value)){ 
value = value.replace('#', ''); 
return "#" + (value.length == 3 ? value.replace(/^(\w)(\w)(\w)$/, '$1$1$2$2$3$3') : value); 
} 
return value; 
} 
} 
window.onload = function(){ 
new Gradient("text1",{width:800,height:100,angle:90,"color-stop":["0,red","16,orange","32,yellow","48,green","64,blue","80,indigo","100,violet"]}) 
new Gradient("text2",{width:800,height:100,angle:0,"color-stop":["0,red","16,orange","32,yellow","48,green","64,blue","80,indigo","100,violet"]}) 
new Gradient("text3",{width:800,height:100,angle:45,"color-stop":["0,red","16,orange","32,yellow","48,green","64,blue","80,indigo","100,violet"]}) 
} 
</ script> 
<div id="text1" class="gradient">javascript线性渐变 by 司徒正美 实现多重水平渐变效果</div>

<div id="text2" class="gradient">javascript线性渐变 by 司徒正美 实现多重垂直渐变效果</div>

<div id="text3" class="gradient">javascript线性渐变 by 司徒正美 实现多重角度渐变效果</div>

[Ctrl+A 全选注:如需引入外部Js需刷新才能执行]