gradutils.js

// Various generic utilities to deal with a linear gradient

define(["./_base", "dojo/_base/lang", "./matrix", "dcolor/Color", "dcolor/utils"],
	function (g, lang, m, Color, colorUtils) {

		var gradutils = g.gradutils = {};

		function findColor(o, c) {
			if (o <= 0) {
				return c[0].color;
			}
			var len = c.length;
			if (o >= 1) {
				return c[len - 1].color;
			}
			//TODO: use binary search
			for (var i = 0; i < len; ++i) {
				var stop = c[i];
				if (stop.offset >= o) {
					if (i) {
						var prev = c[i - 1];
						return colorUtils.blendColors(new Color(prev.color), new Color(stop.color),
							(o - prev.offset) / (stop.offset - prev.offset));
					}
					return stop.color;
				}
			}
			return c[len - 1].color;
		}

		gradutils.getColor = function (fill, pt) {
			// summary:
			//		sample a color from a gradient using a point
			// fill: Object
			//		fill object
			// pt: gfx.Point
			//		point where to sample a color
			var o;
			if (fill) {
				switch (fill.type) {
				case "linear":
					var angle = Math.atan2(fill.y2 - fill.y1,
						fill.x2 - fill.x1), rotation = m.rotate(-angle), projection = m.project(fill.x2 - fill.x1,
						fill.y2 - fill.y1), p = m.multiplyPoint(projection, pt), pf1 = m.multiplyPoint(projection,
						fill.x1, fill.y1), pf2 = m.multiplyPoint(projection, fill.x2,
						fill.y2), scale = m.multiplyPoint(rotation, pf2.x - pf1.x, pf2.y - pf1.y).x;
					o = m.multiplyPoint(rotation, p.x - pf1.x, p.y - pf1.y).x / scale;
					break;
				case "radial":
					var dx = pt.x - fill.cx, dy = pt.y - fill.cy;
					o = Math.sqrt(dx * dx + dy * dy) / fill.r;
					break;
				}
				return findColor(o, fill.colors);	// dcolor/Color
			}
			// simple color
			return new Color(fill || [0, 0, 0, 0]);	// dcolor/Color
		};

		gradutils.reverse = function (fill) {
			// summary:
			//		reverses a gradient
			// fill: Object
			//		fill object
			if (fill) {
				switch (fill.type) {
				case "linear":
				case "radial":
					fill = lang.delegate(fill);
					if (fill.colors) {
						var c = fill.colors, l = c.length, i = 0, stop, n = fill.colors = new Array(c.length);
						for (; i < l; ++i) {
							stop = c[i];
							n[i] = {
								offset: 1 - stop.offset,
								color: stop.color
							};
						}
						n.sort(function (a, b) {
							return a.offset - b.offset;
						});
					}
					break;
				}
			}
			return fill;	// Object
		};

		return gradutils;
	});