New clip convex-hull routine

src/path/Curve.js

@@ -1380,6 +1380,8 @@ new function() { // Scope for methods that require numerical integration
 	 * Calculating convex-hull is much easier than a set of arbitrary points.
 	 *
 	 * The convex-hull is returned as two parts [TOP, BOTTOM]:
+	 * (TOP and BOTTOM are in a coordinate space where y increases
+	 * 	upwards with origin at bottom-left)
 	 *		part that lies above the 'median' (line connecting end points of the curve)
 	 * 		and part that lies below the median.
 	 */
@@ -1434,7 +1436,51 @@ new function() { // Scope for methods that require numerical integration
 	/**
 	 * Clips the convex-hull and returns [tmin, tmax] for the curve contained
 	 */
-	function clipConvexHull (hull, dmin, dmax) {
+	function clipConvexHull(hull, dmin, dmax) {
+		function clipCHull(hull_top, hull_bottom, dmin, dmax) {
+			var tProxy, tVal = null, i, li, px, py, qx, qy;
+			for (i = 0, li = hull_bottom.length-1; i < li; i++) {
+				py = hull_bottom[i][1];
+				qy = hull_bottom[i+1][1];
+				if (py < qy)
+					tProxy = null;
+				else if (qy <= dmax) {
+					px = hull_bottom[i][0];
+					qx = hull_bottom[i+1][0];
+					tProxy = px + (dmax  - py) * (qx - px) / (qy - py);
+				} else
+					// Try the next chain
+					continue;
+				// We got a proxy-t;
+				break;
+			}
+			if (hull_top[0][1] <= dmax)
+				tProxy = hull_top[0][0];
+			for (i = 0, li = hull_top.length-1; i < li; i++) {
+				py = hull_top[i][1];
+				qy = hull_top[i+1][1];
+				if (py >= dmin)
+					tVal = tProxy;
+				else if (py > qy)
+					tVal = null;
+				else if (qy >= dmin) {
+					px = hull_top[i][0];
+					qx = hull_top[i+1][0];
+					tVal = px + (dmin  - py) * (qx - px) / (qy - py);
+				} else
+					continue;
+				break;
+			}
+			return tVal;
+		}
+
+		var tmin, tmax, top = hull[0], bottom = hull[1];
+		tmin = clipCHull(top, bottom, dmin, dmax);
+		top.reverse();
+		bottom.reverse();
+		tmax = clipCHull(top, bottom, dmin, dmax);
+
+		return [tmin, tmax];
 	}
 /*#*/ } // __options.fatline
 
@@ -1536,6 +1582,8 @@ new function() { // Scope for methods that require numerical integration
 			return locations;
 		},
 
-		getConvexHull: getConvexHull
+		getConvexHull: getConvexHull,
+
+		clipConvexHull: clipConvexHull
 	}};
 });