上一部分给出的函数已经完全地实现了跨浏览器了，但在IE的实现是极其低劣，动用了多个table以及一向为人所诟病的滤镜。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。
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"
}
var htmlcolor = {aliceblue: "#f0f8ff", amethyst: "#96c", antiquewhite: "#faebd7", aqua: "#0ff", aquamarine: "#7fffd4", azure: "#f0ffff", beige: "#f5f5dc", bisque: "#ffe4c4", black: "#000", blanchedalmond: "#ffebcd", blue: "#00f", blueviolet: "#8a2be2", brown: "#a52a2a", burlywood: "#deb887", cadetblue: "#5f9ea0", chartreuse: "#7fff00", chocolate: "#d2691e", coral: "#ff7f50", cornflowerblue: "#6495ed", cornsilk: "#fff8dc", crimson: "#dc143c", cyan: "#0ff", darkblue: "#00008b", darkcyan: "#008b8b", darkgoldenrod: "#b8860b", darkgray: "#a9a9a9", darkgreen: "#006400", darkkhaki: "#bdb76b", darkmagenta: "#8b008b", darkolivegreen: "#556b2f", darkorange: "#ff8c00", darkorchid: "#9932cc", darkred: "#8b0000", darksalmon: "#e9967a", darkseagreen: "#8fbc8f", darkslateblue: "#483d8b", darkslategray: "#2f4f4f", darkturquoise: "#00ced1", darkviolet: "#9400d3", deeppink: "#ff1493", deepskyblue: "#00bfff", dimgray: "#696969", dodgerblue: "#1e90ff", firebrick: "#b22222", floralwhite: "#fffaf0", forestgreen: "#228b22", fuchsia: "#f0f", gainsboro: "#dcdcdc", ghostwhite: "#f8f8ff", gold: "#ffd700", goldenrod: "#daa520", gray: "#808080", green: "#008000", greenyellow: "#adff2f", honeydew: "#f0fff0", hotpink: "#ff69b4", indianred: "#cd5c5c", indigo: "#4b0082", ivory: "#fffff0", khaki: "#f0e68c", lavender: "#e6e6fa", lavenderblush: "#fff0f5", lawngreen: "#7cfc00", lemonchiffon: "#fffacd", lightblue: "#add8e6", lightcoral: "#f08080", lightcyan: "#e0ffff", lightgoldenrodyellow: "#fafad2", lightgreen: "#90ee90", lightgrey: "#d3d3d3", lightpink: "#ffb6c1", lightsalmon: "#ffa07a", lightsalmon: "#ffa07a", lightseagreen: "#20b2aa", lightskyblue: "#87cefa", lightslategray: "#789", lightsteelblue: "#b0c4de", lightyellow: "#ffffe0", lime: "#0f0", limegreen: "#32cd32", linen: "#faf0e6", magenta: "#f0f", maroon: "#800000", mediumaquamarine: "#66cdaa", mediumblue: "#0000cd", mediumorchid: "#ba55d3", mediumpurple: "#9370db", mediumseagreen: "#3cb371", mediumslateblue: "#7b68ee", mediumslateblue: "#7b68ee", mediumspringgreen: "#00fa9a", mediumturquoise: "#48d1cc", mediumvioletred: "#c71585", midnightblue: "#191970", mintcream: "#f5fffa", mistyrose: "#ffe4e1", moccasin: "#ffe4b5", navajowhite: "#ffdead", navy: "#000080", oldlace: "#fdf5e6", olive: "#808000", olivedrab: "#6b8e23", orange: "#ffa500", orangered: "#ff4500", orchid: "#da70d6", palegoldenrod: "#eee8aa", palegreen: "#98fb98", paleturquoise: "#afeeee", palevioletred: "#db7093", papayawhip: "#ffefd5", peachpuff: "#ffdab9", peru: "#cd853f", pink: "#ffc0cb", plum: "#dda0dd", powderblue: "#b0e0e6", purple: "#800080", red: "#f00", rosybrown: "#bc8f8f", royalblue: "#4169e1", saddlebrown: "#8b4513", salmon: "#fa8072", sandybrown: "#f4a460", seagreen: "#2e8b57", seashell: "#fff5ee", sienna: "#a0522d", silver: "#c0c0c0", skyblue: "#87ceeb", slateblue: "#6a5acd", slategray: "#708090", snow: "#fffafa", springgreen: "#00ff7f", steelblue: "#4682b4", tan: "#d2b48c", teal: "#008080", thistle: "#d8bfd8", tomato: "#ff6347", turquoise: "#40e0d0", violet: "#ee82ee", wheat: "#f5deb3", white: "#fff", whitesmoke: "#f5f5f5", yellow: "#ff0", yellowgreen: "#9acd32"}
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：
javascript线性渐变 by 司徒正美 实现多重水平渐变效果
javascript线性渐变 by 司徒正美 javascript线性渐变 by 司徒正美 实现多重水平渐变效果
javascript线性渐变 by 司徒正美 实现多重垂直渐变效果
运行代码
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。
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。
javascript线性渐变 by 司徒正美 javascript线性渐变 by 司徒正美 实现多重水平渐变效果
javascript线性渐变 by 司徒正美 实现多重垂直渐变效果
javascript线性渐变 by 司徒正美 实现多重角度渐变效果
运行代码
//从老外找到的另一种方法，可惜不支持角度渐变 //原理是动态创建一个canvas对象（不用加入DOM树） //利用其toDataURL() 生成一图片，然后做成渐变体的背景图片，不需要在结构层添加任何东西，妙！ var setGradient = (function(){ //private variables; var p_dCanvas = document.createElement('canvas'); var p_useCanvas = !!( typeof(p_dCanvas.getContext) == 'function'); var p_dCtx = p_useCanvas?p_dCanvas.getContext('2d'):null; var p_isIE = /*@cc_on!@*/false; //test if toDataURL() is supported by Canvas since Safari may not support it try{ p_dCtx.canvas.toDataURL() }catch(err){ p_useCanvas = false ; }; if(p_useCanvas){ return function (dEl , sColor1 , sColor2 , bRepeatY ){ if(typeof(dEl) == 'string') dEl = document.getElementById(dEl); if(!dEl) return false; var nW = dEl.offsetWidth; var nH = dEl.offsetHeight; p_dCanvas.width = nW; p_dCanvas.height = nH; var dGradient; var sRepeat; // Create gradients if(bRepeatY){ dGradient = p_dCtx.createLinearGradient(0,0,nW,0); sRepeat = 'repeat-y'; }else{ dGradient = p_dCtx.createLinearGradient(0,0,0,nH); sRepeat = 'repeat-x'; } dGradient.addColorStop(0,sColor1); dGradient.addColorStop(1,sColor2); p_dCtx.fillStyle = dGradient ; p_dCtx.fillRect(0,0,nW,nH); var sDataUrl = p_dCtx.canvas.toDataURL('image/png'); with(dEl.style){ backgroundRepeat = sRepeat; backgroundImage = 'url(' + sDataUrl + ')'; backgroundColor = sColor2; }; } }else if(p_isIE){ p_dCanvas = p_useCanvas = p_dCtx = null; return function (dEl , sColor1 , sColor2 , bRepeatY){ if(typeof(dEl) == 'string') dEl = document.getElementById(dEl); if(!dEl) return false; dEl.style.zoom = 1; var sF = dEl.currentStyle.filter; dEl.style.filter += ' ' + ['progid:DXImageTransform.Microsoft.gradient( GradientType=', +(!!bRepeatY ),',enabled=true,startColorstr=',sColor1,', endColorstr=',sColor2,')'].join(''); }; }else{ p_dCanvas = p_useCanvas = p_dCtx = null; return function(dEl , sColor1 , sColor2 ){ if(typeof(dEl) == 'string') dEl = document.getElementById(dEl); if(!dEl) return false; with(dEl.style){ backgroundColor = sColor2; }; //alert('your browser does not support gradient effet'); } } })();
