Add an ellipse to resolve point ambiguity when dragging

(closes #3536)

css/20_map.css

@@ -49,6 +49,15 @@ g.point.active, g.point.active * {
     pointer-events: none;
 }
 
+g.point ellipse.stroke {
+    display: none;
+}
+
+.mode-drag-node g.point.active ellipse.stroke {
+    display: block;
+}
+
+
 /* vertices and midpoints */
 
 g.vertex .fill {

modules/svg/points.js

@@ -43,6 +43,13 @@ export function svgPoints(projection, context) {
         enter.append('path')
             .call(markerPath, 'shadow');
 
+        enter.append('ellipse')
+            .attr('cx', 0.5)
+            .attr('cy', 1)
+            .attr('rx', 6.5)
+            .attr('ry', 3)
+            .attr('class', 'stroke');
+
         enter.append('path')
             .call(markerPath, 'stroke');