polyline: Added encode/decodeFlatCoordinates() functions

src/ol/parser/polyline.js

@@ -1,6 +1,73 @@
 goog.provide('ol.parser.polyline');
 
 
+/**
+ * Encode a list of coordinates in a flat array and return an encoded string
+ *
+ * @param {Array.<number>} flat_points A flat array of coordinates.
+ * @param {number=} opt_dimension The dimension of the coordinates in the array.
+ * @return {string} The encoded string.
+ */
+ol.parser.polyline.encodeFlatCoordinates =
+    function(flat_points, opt_dimension) {
+  var dimension = opt_dimension || 2;
+
+  var last_point = new Array(dimension);
+  for (var i = 0; i < dimension; ++i)
+    last_point[i] = 0;
+
+  var encoded = '', flat_points_length = flat_points.length;
+  for (var i = 0; i < flat_points_length;) {
+    for (var d = 0; d < dimension; ++d) {
+      var part = Math.round(flat_points[i++] * 1e5);
+      var delta = part - last_point[d];
+      last_point[d] = part;
+
+      encoded += ol.parser.polyline.encodeSignedInteger(delta);
+    }
+  }
+
+  return encoded;
+};
+
+
+/**
+ * Decode a list of coordinates from an encoded string into a flat array
+ *
+ * @param {string} encoded An encoded string.
+ * @param {number=} opt_dimension The dimension of the coordinates in the
+ * encoded string.
+ * @return {Array.<number>} A flat array of coordinates.
+ */
+ol.parser.polyline.decodeFlatCoordinates = function(encoded, opt_dimension) {
+  var dimension = opt_dimension || 2;
+
+  var last_point = new Array(dimension);
+  for (var i = 0; i < dimension; ++i)
+    last_point[i] = 0;
+
+  var flat_points = new Array(), encoded_length = encoded.length;
+  for (var i = 0; i < encoded_length;) {
+    for (var d = 0; d < dimension; ++d) {
+      var result = 0;
+      var shift = 0;
+
+      var b;
+      do {
+        b = encoded.charCodeAt(i++) - 63;
+        result |= (b & 0x1f) << shift;
+        shift += 5;
+      } while (b >= 0x20);
+
+      last_point[d] += (result & 1) ? ~(result >> 1) : (result >> 1);
+      flat_points.push(last_point[d] / 1e5);
+    }
+  }
+
+  return flat_points;
+};
+
+
 /**
  * Encode one single floating point number and return an encoded string
  *

test/spec/ol/parser/polyline.test.js

@@ -2,6 +2,28 @@ goog.provide('ol.test.parser.polyline');
 
 describe('ol.parser.polyline', function() {
 
+  var flat_points = [38.50000, -120.20000,
+                     40.70000, -120.95000,
+                     43.25200, -126.45300];
+
+  describe('encodeFlatCoordinates', function() {
+    it('returns expected value', function() {
+      var encodeFlatCoordinates = ol.parser.polyline.encodeFlatCoordinates;
+
+      expect(encodeFlatCoordinates(
+          flat_points)).toEqual('_p~iF~ps|U_ulLnnqC_mqNvxq`@');
+    });
+  });
+
+  describe('decodeFlatCoordinates', function() {
+    it('returns expected value', function() {
+      var decodeFlatCoordinates = ol.parser.polyline.decodeFlatCoordinates;
+
+      expect(decodeFlatCoordinates(
+          '_p~iF~ps|U_ulLnnqC_mqNvxq`@')).toEqual(flat_points);
+    });
+  });
+
   describe('encodeFloat', function() {
     it('returns expected value', function() {
       var encodeFloat = ol.parser.polyline.encodeFloat;