Add snapping abilities on circles

src/ol/coordinate.js

@@ -26,6 +26,37 @@ ol.coordinate.add = function(coordinate, delta) {
 };
 
 
+/**
+ * Calculates the point closest to the passed coordinate on the passed circle.
+ *
+ * @param {ol.Coordinate} coordinate The coordinate.
+ * @param {ol.geom.Circle} circle The circle.
+ * @return {ol.Coordinate} Closest point on the circumference
+ */
+ol.coordinate.closestOnCircle = function(coordinate, circle) {
+  var r = circle.getRadius();
+  var center = circle.getCenter();
+  var x0 = center[0];
+  var y0 = center[1];
+  var x1 = coordinate[0];
+  var y1 = coordinate[1];
+
+  var dx = x1 - x0;
+  var dy = y1 - y0;
+  if (dx === 0 && dy === 0) {
+    dx = 1;
+  }
+  var d = Math.sqrt(dx * dx + dy * dy);
+
+  var x, y;
+
+  x = x0 + r * dx / d;
+  y = y0 + r * dy / d;
+
+  return [x, y];
+};
+
+
 /**
  * Calculates the point closest to the passed coordinate on the passed segment.
  * This is the foot of the perpendicular of the coordinate to the segment when