Check for valid multipolygon geometry when dragging nodes

(this can get a bit expensive for large/complex multipolygons)

modules/geo/geom.js

@@ -157,6 +157,20 @@ export function geoPathIntersections(path1, path2) {
     return intersections;
 }
 
+export function geoPathHasIntersections(path1, path2) {
+    for (var i = 0; i < path1.length - 1; i++) {
+        for (var j = 0; j < path2.length - 1; j++) {
+            var a = [ path1[i], path1[i+1] ];
+            var b = [ path2[j], path2[j+1] ];
+            var hit = geoLineIntersection(a, b);
+            if (hit) {
+                return true;
+            }
+        }
+    }
+    return false;
+}
+
 
 // Return whether point is contained in polygon.
 //
@@ -195,24 +209,13 @@ export function geoPolygonContainsPolygon(outer, inner) {
 
 
 export function geoPolygonIntersectsPolygon(outer, inner, checkSegments) {
-    function testSegments(outer, inner) {
-        for (var i = 0; i < outer.length - 1; i++) {
-            for (var j = 0; j < inner.length - 1; j++) {
-                var a = [ outer[i], outer[i + 1] ];
-                var b = [ inner[j], inner[j + 1] ];
-                if (geoLineIntersection(a, b)) return true;
-            }
-        }
-        return false;
-    }
-
     function testPoints(outer, inner) {
         return _some(inner, function(point) {
             return geoPointInPolygon(point, outer);
         });
     }
 
-   return testPoints(outer, inner) || (!!checkSegments && testSegments(outer, inner));
+   return testPoints(outer, inner) || (!!checkSegments && geoPathHasIntersections(outer, inner));
 }
 
 

modules/geo/index.js

@@ -16,6 +16,7 @@ export { geoEdgeEqual } from './geom.js';
 export { geoHasSelfIntersections } from './geom.js';
 export { geoRotate } from './geom.js';
 export { geoLineIntersection } from './geom.js';
+export { geoPathHasIntersections } from './geom.js';
 export { geoPathIntersections } from './geom.js';
 export { geoPathLength } from './geom.js';
 export { geoPointInPolygon } from './geom.js';

modules/modes/drag_node.js

@@ -1,3 +1,5 @@
+import _find from 'lodash-es/find';
+
 import {
     event as d3_event,
     select as d3_select
@@ -21,12 +23,13 @@ import {
 import {
     geoChooseEdge,
     geoHasSelfIntersections,
+    geoPathHasIntersections,
     geoVecSubtract,
     geoViewportEdge
 } from '../geo';
 
 import { modeBrowse, modeSelect } from './index';
-import { osmNode } from '../osm';
+import { osmJoinWays, osmNode } from '../osm';
 import { uiFlash } from '../ui';
 
 
@@ -174,15 +177,53 @@ export function modeDragNode(context) {
 
     function invalidGeometry(entity, graph) {
         var parents = graph.parentWays(entity);
+        var i, j, k;
 
-        for (var i = 0; i < parents.length; i++) {
+        for (i = 0; i < parents.length; i++) {
             var parent = parents[i];
-            var nodes = parent.nodes.map(function(nodeID) { return graph.entity(nodeID); });
-            if (parent.isClosed()) {
-                if (geoHasSelfIntersections(nodes, entity.id)) {
+            var nodes = [];
+            var activeIndex = null;    // which multipolygon ring contains node being dragged
+
+            // test any parent multipolygons for valid geometry
+            var relations = graph.parentRelations(parent);
+            for (j = 0; j < relations.length; j++) {
+                if (!relations[j].isMultipolygon()) continue;
+
+                var rings = osmJoinWays(relations[j].members, graph);
+
+                // find active ring and test it for self intersections
+                for (k = 0; k < rings.length; k++) {
+                    nodes = rings[k].nodes;
+                    if (_find(nodes, function(n) { return n.id === entity.id; })) {
+                        activeIndex = k;
+                        if (geoHasSelfIntersections(nodes, entity.id)) {
+                            return true;
+                        }
+                    }
+                    rings[k].coords = nodes.map(function(n) { return n.loc; });
+                }
+
+                // test active ring for intersections with other rings in the multipolygon
+                for (k = 0; k < rings.length; k++) {
+                    if (k === activeIndex) continue;
+
+                    // make sure active ring doesnt cross passive rings
+                    if (geoPathHasIntersections(rings[activeIndex].coords, rings[k].coords)) {
+                        return true;
+                    }
+                }
+            }
+
+
+            // If we still haven't tested this node's parent way for self-intersections.
+            // (because it's not a member of a multipolygon), test it now.
+            if (activeIndex !== null && parent.isClosed()) {
+                nodes = parent.nodes.map(function(nodeID) { return graph.entity(nodeID); });
+                if (nodes.length && geoHasSelfIntersections(nodes, entity.id)) {
                     return true;
                 }
             }
+
         }
 
         return false;

test/spec/geo/geom.js

@@ -342,6 +342,12 @@ describe('iD.geo - geometry', function() {
             expect(iD.geoPolygonIntersectsPolygon(outer, inner)).to.be.true;
         });
 
+        it('returns false when inner polygon fully contains outer', function() {
+            var inner = [[0, 0], [0, 3], [3, 3], [3, 0], [0, 0]];
+            var outer = [[1, 1], [1, 2], [2, 2], [2, 1], [1, 1]];
+            expect(iD.geoPolygonIntersectsPolygon(outer, inner)).to.be.false;
+        });
+
         it('returns true when outer polygon partially contains inner (some vertices contained)', function() {
             var outer = [[0, 0], [0, 3], [3, 3], [3, 0], [0, 0]];
             var inner = [[-1, -1], [1, 2], [2, 2], [2, 1], [1, 1]];