Handle doughtnuts of islands of dough...

The logic to determine which, if any, ring encloses another given ring depends on starting with the vertex that comes earliest in the sweep-line pass. This commit fixes the situation so that this bit of logic starts from the correct vertex. Fixes #38 Closes #39
mfogel · Oct 17, 2018 · db3acf9 · db3acf9
1 parent 2cbfbd2
commit db3acf9
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Showing 3 changed files with 40 additions and 7 deletions.
diff --git a/src/geom-out.js b/src/geom-out.js
@@ -1,4 +1,5 @@
 import { compareVectorAngles } from './vector'
+import SweepEvent from './sweep-event'
 
 export class RingOut {
   /* Given the segments from the sweep line pass, compute & return a series
@@ -147,8 +148,15 @@ export class RingOut {
 
   /* Returns the ring that encloses this one, if any */
   _enclosingRing () {
-    let prevSeg = this.events[0].segment.prevInResult
-    while (prevSeg && prevSeg.ringOut === this) prevSeg = prevSeg.prevInResult
+    // start with the ealier sweep line event so that the prevSeg
+    // chain doesn't lead us inside of a loop of ours
+    let leftMostEvt = this.events[0]
+    for (let i = 1, iMax = this.events.length; i < iMax; i++) {
+      const evt = this.events[i]
+      if (SweepEvent.compare(leftMostEvt, evt) > 0) leftMostEvt = evt
+    }
+
+    let prevSeg = leftMostEvt.segment.prevInResult
     let prevPrevSeg = prevSeg ? prevSeg.prevInResult : null
 
     while (true) {

diff --git a/test/end-to-end/issue-38/args.geojson b/test/end-to-end/issue-38/args.geojson
@@ -9,10 +9,10 @@
         "coordinates": [
           [
             [-76.377, 38.782],
-            [-76.385, 38.765],
-            [-76.393, 38.758],
-            [-76.343, 38.714],
             [-76.509, 38.751],
+            [-76.343, 38.714],
+            [-76.393, 38.758],
+            [-76.385, 38.765],
             [-76.377, 38.782]
           ]
         ]
@@ -26,8 +26,8 @@
         "coordinates": [
           [
             [-76.377, 38.749],
-            [-76.388, 38.755],
             [-76.383, 38.756],
+            [-76.388, 38.755],
             [-76.377, 38.749]
           ]
         ]
@@ -41,8 +41,8 @@
         "coordinates": [
           [
             [-76.377, 38.782],
-            [-76.339, 38.721],
             [-76.376, 38.742],
+            [-76.339, 38.721],
             [-76.377, 38.782]
           ]
         ]

diff --git a/test/end-to-end/issue-38/union.geojson b/test/end-to-end/issue-38/union.geojson
@@ -4,6 +4,31 @@
   "geometry": {
     "type": "MultiPolygon",
     "coordinates": [
+      [
+        [
+          [-76.509, 38.751],
+          [-76.343, 38.714],
+          [-76.37267128027682, 38.74011072664359],
+          [-76.339, 38.721],
+          [-76.377, 38.782],
+          [-76.509, 38.751]
+        ],
+        [
+          [-76.377, 38.782],
+          [-76.37602658486709, 38.743063394683034],
+          [-76.393, 38.758],
+          [-76.385, 38.765],
+          [-76.377, 38.782]
+        ]
+      ],
+      [
+        [
+          [-76.388, 38.755],
+          [-76.377, 38.749],
+          [-76.383, 38.756],
+          [-76.388, 38.755]
+        ]
+      ]
     ]
   }
 }