Significantly improved line simplification performance

CHANGELOG.md

@@ -18,6 +18,7 @@ Leaflet Changelog
  * Map now preserves its center after resize.
  * When panning to another copy of the world (that's infinite horizontally), map overlays now jump to corresponding positions. [#273](https://github.com/CloudMade/Leaflet/issues/273)
  * Limited maximum zoom change on a single mouse wheel movement (so you won't zoom across the whole zoom range in one scroll). [#149](https://github.com/CloudMade/Leaflet/issues/149)
+ * Significantly improved line simplification performance (noticeable when rendering polylines/polygons with tens of thousands of points)
  * Improved circles performance by not drawing them if they're off the clip region.
 
 #### API improvements

src/geometry/LineUtil.js

@@ -13,73 +13,81 @@ L.LineUtil = {
 			return points.slice();
 		}
 
+		var sqTolerance = tolerance * tolerance;
+
 		// stage 1: vertex reduction
-		points = this.reducePoints(points, tolerance);
+		points = this._reducePoints(points, sqTolerance);
 
 		// stage 2: Douglas-Peucker simplification
-		points = this.simplifyDP(points, tolerance);
+		points = this._simplifyDP(points, sqTolerance);
 
 		return points;
 	},
 
 	// distance from a point to a segment between two points
 	pointToSegmentDistance:  function (/*Point*/ p, /*Point*/ p1, /*Point*/ p2) {
-		return Math.sqrt(this._sqPointToSegmentDist(p, p1, p2));
+		return Math.sqrt(this._sqClosestPointOnSegment(p, p1, p2, true));
 	},
 
 	closestPointOnSegment: function (/*Point*/ p, /*Point*/ p1, /*Point*/ p2) {
-		var point = this._sqClosestPointOnSegment(p, p1, p2);
+		return this._sqClosestPointOnSegment(p, p1, p2);
-		point.distance = Math.sqrt(point._sqDist);
-		return point;
 	},
 
 	// Douglas-Peucker simplification, see http://en.wikipedia.org/wiki/Douglas-Peucker_algorithm
-	simplifyDP: function (points, tol) {
+	_simplifyDP: function (points, sqTolerance) {
-		var maxDist2 = 0,
-			index = 0,
-			t2 = tol * tol,
-			len = points.length,
-			i, dist2;
 
-		if (len < 3) {
+		var len = points.length,
-			return points;
+			ArrayConstructor = typeof Uint8Array !== 'undefined' ? Uint8Array : Array,
+			markers = new ArrayConstructor(len);
+
+		markers[0] = markers[len - 1] = 1;
+
+		this._simplifyDPStep(points, markers, sqTolerance, 0, len - 1);
+
+		var i,
+			newPoints = [];
+
+		for (i = 0; i < len; i++) {
+			if (markers[i]) {
+				newPoints.push(points[i]);
+			}
 		}
 
-		for (i = 0; i < len - 1; i++) {
+		return newPoints;
-			dist2 = this._sqPointToSegmentDist(points[i], points[0], points[len - 1]);
+	},
-			if (dist2 > maxDist2) {
+
+	_simplifyDPStep: function (points, markers, sqTolerance, first, last) {
+
+		var maxSqDist = 0,
+			index, i, sqDist;
+
+		for (i = first + 1; i <= last - 1; i++) {
+			sqDist = this._sqClosestPointOnSegment(points[i], points[first], points[last], true);
+
+			if (sqDist > maxSqDist) {
 				index = i;
-				maxDist2 = dist2;
+				maxSqDist = sqDist;
 			}
 		}
 
-		var part1, part2;
+		if (maxSqDist > sqTolerance) {
+			markers[index] = 1;
 
-		if (maxDist2 >= t2) {
+			this._simplifyDPStep(points, markers, sqTolerance, first, index);
-			part1 = points.slice(0, index);
+			this._simplifyDPStep(points, markers, sqTolerance, index, last);
-			part2 = points.slice(index);
-
-			part1 = this.simplifyDP(part1, tol);
-			part2 = this.simplifyDP(part2, tol);
-
-			return part1.concat(part2);
-		} else {
-			return [points[0], points[len - 1]];
 		}
 	},
 
 	// reduce points that are too close to each other to a single point
-	reducePoints: function (points, tol) {
+	_reducePoints: function (points, sqTolerance) {
-		var reducedPoints = [points[0]],
+		var reducedPoints = [points[0]];
-			t2 = tol * tol;
 
 		for (var i = 1, prev = 0, len = points.length; i < len; i++) {
-			if (this._sqDist(points[i], points[prev]) < t2) {
+			if (this._sqDist(points[i], points[prev]) > sqTolerance) {
-				continue;
-			}
 				reducedPoints.push(points[i]);
 				prev = i;
 			}
+		}
 		if (prev < len - 1) {
 			reducedPoints.push(points[len - 1]);
 		}
@@ -168,27 +176,30 @@ L.LineUtil = {
 		return dx * dx + dy * dy;
 	},
 
-	// return closest point on segment with attribute _sqDist - square distance to segment
+	// return closest point on segment or distance to that point
-	_sqClosestPointOnSegment: function (p, p1, p2) {
+	_sqClosestPointOnSegment: function (p, p1, p2, sqDist) {
-		var x2 = p2.x - p1.x,
+		var x = p1.x,
-			y2 = p2.y - p1.y,
+			y = p1.y,
-			apoint = p1;
+			dx = p2.x - x,
-		if (x2 || y2) {
+			dy = p2.y - y,
-			var dot = (p.x - p1.x) * x2 + (p.y - p1.y) * y2,
+			dot = dx * dx + dy * dy,
-				t = dot / this._sqDist(p1, p2);
+			t;
+
+		if (dot > 0) {
+			t = ((p.x - x) * dx + (p.y - y) * dy) / dot;
 
 			if (t > 1) {
-				apoint = p2;
+				x = p2.x;
+				y = p2.y;
 			} else if (t > 0) {
-				apoint = new L.Point(p1.x + x2 * t, p1.y + y2 * t);
+				x += dx * t;
+				y += dy * t;
 			}
 		}
-		apoint._sqDist = this._sqDist(p, apoint);
-		return apoint;
-	},
 
-	// distance from a point to a segment between two points
+		dx = p.x - x;
-	_sqPointToSegmentDist: function (p, p1, p2) {
+		dy = p.y - y;
-		return this._sqClosestPointOnSegment(p, p1, p2)._sqDist;
+
+		return sqDist ? dx * dx + dy * dy : new L.Point(x, y);
 	}
 };