//颜色阶梯过渡（均匀渐变）Gradient算法
//Gradient = Start+ (End-Start) / Step * N

function gradientColor(startColor, endColor, step) {
    if (startColor && endColor) {
        if (startColor[0] !== '#') {
            startColor = this.colorHex(startColor);
        }
        if (endColor[0] !== '#') {
            endColor = this.colorHex(endColor);
        }
        startRGB = this.colorRgb(startColor);//转换为rgb数组模式
        startR = startRGB[0];
        startG = startRGB[1];
        startB = startRGB[2];

        endRGB = this.colorRgb(endColor);
        endR = endRGB[0];
        endG = endRGB[1];
        endB = endRGB[2];

        sR = (endR - startR) / step;//总差值
        sG = (endG - startG) / step;
        sB = (endB - startB) / step;

        var colorArr = [];
        for (var i = 0; i < step; i++) {
            //计算每一步的hex值
            var hex = this.colorHex('rgb(' + parseInt((sR * i + startR)) + ',' + parseInt((sG * i + startG)) + ',' + parseInt((sB * i + startB)) + ')');
            colorArr.push(hex);
        }
        return colorArr;
    }
    return this;
}

// 将hex表示方式转换为rgb表示方式(这里返回rgb数组模式)
gradientColor.prototype.colorRgb = function (sColor) {
    var reg = /^#([0-9a-fA-f]{3}|[0-9a-fA-f]{6})$/;
    var sColor = sColor.toLowerCase();
    if (sColor && reg.test(sColor)) {
        if (sColor.length === 4) {
            var sColorNew = "#";
            for (var i = 1; i < 4; i += 1) {
                sColorNew += sColor.slice(i, i + 1).concat(sColor.slice(i, i + 1));
            }
            sColor = sColorNew;
        }
        //处理六位的颜色值
        var sColorChange = [];
        for (var i = 1; i < 7; i += 2) {
            sColorChange.push(parseInt("0x" + sColor.slice(i, i + 2)));
        }
        return sColorChange;
    } else {
        return sColor;
    }
};

// 将rgb表示方式转换为hex表示方式
gradientColor.prototype.colorHex = function (rgb) {
    var _this = rgb;
    var reg = /^#([0-9a-fA-f]{3}|[0-9a-fA-f]{6})$/;
    if (/^(rgb|RGB)/.test(_this)) {
        var str = _this.replace(/(rgb|RGB)*/g, "");
        str = str.replace("(", "").replace(")", "");
        var aColor = str.split(",");
        var strHex = "#";
        for (var i = 0; i < aColor.length; i++) {
            var hex = Number(aColor[i]).toString(16);
            hex = hex.length === 1 ? 0 + '' + hex : hex;// 保证每个rgb的值为2位
            if (hex === "0") {
                hex += hex;
            }
            strHex += hex;
        }
        if (strHex.length !== 7) {
            strHex = _this;
        }
        return strHex;
    } else if (reg.test(_this)) {
        var aNum = _this.replace(/#/, "").split("");
        if (aNum.length === 6) {
            return _this;
        } else if (aNum.length === 3) {
            var numHex = "#";
            for (var i = 0; i < aNum.length; i += 1) {
                numHex += (aNum[i] + aNum[i]);
            }
            return numHex;
        }
    } else {
        return _this;
    }
};