source: Dev/trunk/src/client/dojox/gfx3d/gradient.js

define(["dojo/_base/lang","./matrix","./vector"], 
        function(lang,m,v){

        var gfx3d = lang.getObject("dojox.gfx3d",true);

        var dist = function(a, b){ return Math.sqrt(Math.pow(b.x - a.x, 2) + Math.pow(b.y - a.y, 2)); };
        var N = 32;

        gfx3d.gradient = function(model, material, center, radius, from, to, matrix){
                // summary:
                //              calculate a cylindrical gradient
                // model: dojox.gfx3d.lighting.Model
                //              color model
                // material: Object
                //              defines visual properties
                // center: Object
                //              center of the cylinder's bottom
                // radius: Number
                //              radius of the cylinder
                // from: Number
                //              from position in radians
                // to: Number
                //              from position in radians
                // matrix: dojox.gfx3d.Matrix3D
                //              the cumulative transformation matrix
                // tolerance: Number
                //              tolerable difference in colors between gradient steps

                var mx = m.normalize(matrix),
                        f = m.multiplyPoint(mx, radius * Math.cos(from) + center.x, radius * Math.sin(from) + center.y, center.z),
                        t = m.multiplyPoint(mx, radius * Math.cos(to)   + center.x, radius * Math.sin(to)   + center.y, center.z),
                        c = m.multiplyPoint(mx, center.x, center.y, center.z), step = (to - from) / N, r = dist(f, t) / 2,
                        mod = model[material.type], fin = material.finish, pmt = material.color,
                        colors = [{offset: 0, color: mod.call(model, v.substract(f, c), fin, pmt)}];

                for(var a = from + step; a < to; a += step){
                        var p = m.multiplyPoint(mx, radius * Math.cos(a) + center.x, radius * Math.sin(a) + center.y, center.z),
                                df = dist(f, p), dt = dist(t, p);
                        colors.push({offset: df / (df + dt), color: mod.call(model, v.substract(p, c), fin, pmt)});
                }
                colors.push({offset: 1, color: mod.call(model, v.substract(t, c), fin, pmt)});

                return {type: "linear", x1: 0, y1: -r, x2: 0, y2: r, colors: colors};
        };

        return gfx3d.gradient;
});