From 5bcbd23ccaed13501bbad2853fc60e116fe8d6b8 Mon Sep 17 00:00:00 2001
From: Hubert Argasinski <hargasinski@locusrobotics.com>
Date: Wed, 8 Jun 2022 18:36:37 -0400
Subject: [PATCH] Fix modifying polygons with overlapping vertices

When a polygonal geometry, where one of the vertices overlaps the first
vertex in the same ring, is modified, ensure the correct vertices are
updated.
---
 src/ol/interaction/Modify.js                  | 27 +++++++++--
 .../spec/ol/interaction/modify.test.js        | 46 +++++++++++++++++++
 2 files changed, 68 insertions(+), 5 deletions(-)

diff --git a/src/ol/interaction/Modify.js b/src/ol/interaction/Modify.js
index 129db2ce90..9158308cbd 100644
--- a/src/ol/interaction/Modify.js
+++ b/src/ol/interaction/Modify.js
@@ -1042,15 +1042,32 @@ class Modify extends PointerInteraction {
           coordinatesEqual(segment[1], vertex) &&
           !componentSegments[uid][1]
         ) {
-          // prevent dragging closed linestrings by the connecting node
           if (
-            (segmentDataMatch.geometry.getType() === GeometryType.LINE_STRING ||
-              segmentDataMatch.geometry.getType() ===
-                GeometryType.MULTI_LINE_STRING) &&
             componentSegments[uid][0] &&
             componentSegments[uid][0].index === 0
           ) {
-            continue;
+            let coordinates = segmentDataMatch.geometry.getCoordinates();
+            switch (segmentDataMatch.geometry.getType()) {
+              // prevent dragging closed linestrings by the connecting node
+              case GeometryType.LINE_STRING:
+              case GeometryType.MULTI_LINE_STRING:
+                continue;
+              // if dragging the first vertex of a polygon, ensure the other segment
+              // belongs to the closing vertex of the linear ring
+              case GeometryType.MULTI_POLYGON:
+                coordinates = coordinates[depth[1]];
+              /* falls through */
+              case GeometryType.POLYGON:
+                if (
+                  segmentDataMatch.index !==
+                  coordinates[depth[0]].length - 2
+                ) {
+                  continue;
+                }
+                break;
+              default:
+              // pass
+            }
           }
 
           this.dragSegments_.push([segmentDataMatch, 1]);
diff --git a/test/browser/spec/ol/interaction/modify.test.js b/test/browser/spec/ol/interaction/modify.test.js
index fe1bcb17bf..3dfab0cac6 100644
--- a/test/browser/spec/ol/interaction/modify.test.js
+++ b/test/browser/spec/ol/interaction/modify.test.js
@@ -419,6 +419,52 @@ describe('ol.interaction.Modify', function () {
       expect(lineFeature.getGeometry().getCoordinates()[2][2]).to.equal(30);
       expect(lineFeature.getGeometry().getCoordinates()[4][2]).to.equal(50);
     });
+
+    it('keeps polygon geometries valid', function () {
+      const overlappingVertexFeature = new Feature({
+        geometry: new Polygon([
+          [
+            [10, 20],
+            [0, 20],
+            [0, 0],
+            [20, 0],
+            [20, 20],
+            [10, 20],
+            [15, 15],
+            [5, 15],
+            [10, 20],
+          ],
+        ]),
+      });
+      features.length = 0;
+      features.push(overlappingVertexFeature);
+
+      const modify = new Modify({
+        features: new Collection(features),
+      });
+      map.addInteraction(modify);
+
+      let coords, exteriorRing;
+      coords = overlappingVertexFeature.getGeometry().getCoordinates();
+      exteriorRing = coords[0];
+
+      expect(exteriorRing.length).to.equal(9);
+      expect(exteriorRing[0]).to.eql(exteriorRing[exteriorRing.length - 1]);
+
+      // move the overlapping vertice
+      simulateEvent('pointermove', 10, -20, null, 0);
+      simulateEvent('pointerdown', 10, -20, null, 0);
+      simulateEvent('pointermove', 10, -25, null, 0);
+      simulateEvent('pointerdrag', 10, -25, null, 0);
+      simulateEvent('pointerup', 10, -25, null, 0);
+
+      coords = overlappingVertexFeature.getGeometry().getCoordinates();
+      exteriorRing = coords[0];
+
+      expect(exteriorRing.length).to.equal(9);
+      expect(exteriorRing[0]).to.eql([10, 25]);
+      expect(exteriorRing[0]).to.eql(exteriorRing[exteriorRing.length - 1]);
+    });
   });
 
   describe('vertex insertion', function () {