LUCENE-9251: Filter equal edges with different value on isEdgeFromPolygon (#1290)

Fix bug in the polygon tessellator where edges with different value on #isEdgeFromPolygon were bot filtered out properly

lucene/CHANGES.txt

@@ -224,6 +224,9 @@ Bug Fixes
 
 * LUCENE-9239: Circle2D#WithinTriangle detects properly if a triangle is Within distance. (Ignacio Vera)
 
+* LUCENE-9251: Fix bug in the polygon tessellator where edges with different value on #isEdgeFromPolygon
+  were bot filtered out properly. (Ignacio Vera)
+
 Other
 ---------------------
 

lucene/core/src/java/org/apache/lucene/geo/Tessellator.java

@@ -435,7 +435,6 @@ final public class Tessellator {
           continue;
         }
         currEar = nextNode;
-
         // If the whole polygon has been iterated over and no more ears can be found.
         if (currEar == stop) {
           switch (state) {
@@ -915,13 +914,14 @@ final public class Tessellator {
       continueIteration = false;
       nextNode = node.next;
       prevNode = node.previous;
-      //We can filter points when they are the same, if not and they are co-linear we can only
-      //remove it if both edges have the same value in .isNextEdgeFromPolygon
-      if (isVertexEquals(node, nextNode)  ||
-          (prevNode.isNextEdgeFromPolygon == node.isNextEdgeFromPolygon &&
+      // we can filter points when:
+      if (isVertexEquals(node, nextNode)  ||   // 1. they are the same,
+          isVertexEquals(prevNode, nextNode) || // 2.- each one starts and ends in each other
+          (prevNode.isNextEdgeFromPolygon == node.isNextEdgeFromPolygon && // 3.- they are co-linear and both edges have the same value in .isNextEdgeFromPolygon
               area(prevNode.getX(), prevNode.getY(), node.getX(), node.getY(), nextNode.getX(), nextNode.getY()) == 0)) {
         // Remove the node
-        removeNode(node, prevNode.isNextEdgeFromPolygon);
+        boolean nextEdgeFromPol = prevNode.isNextEdgeFromPolygon != node.isNextEdgeFromPolygon ? true : prevNode.isNextEdgeFromPolygon;
+        removeNode(node, nextEdgeFromPol);
         node = end = prevNode;
 
         if (node == nextNode) {

lucene/core/src/test/org/apache/lucene/geo/TestTessellator.java

@@ -561,6 +561,18 @@ public class TestTessellator extends LuceneTestCase {
     checkPolygon(wkt);
   }
 
+  @Nightly
+  public void testComplexPolygon40() throws Exception {
+    String wkt = GeoTestUtil.readShape("lucene-9251.wkt.gz");
+    Polygon polygon = (Polygon) SimpleWKTShapeParser.parse(wkt);
+    List<Tessellator.Triangle> tessellation = Tessellator.tessellate(polygon);
+    // calculate the area of big polygons have numerical error
+    assertEquals(area(polygon), area(tessellation), 1e-12);
+    for (Tessellator.Triangle t : tessellation) {
+      checkTriangleEdgesFromPolygon(polygon, t);
+    }
+  }
+
   private void checkPolygon(String wkt) throws Exception {
     Polygon polygon = (Polygon) SimpleWKTShapeParser.parse(wkt);
     List<Tessellator.Triangle> tessellation = Tessellator.tessellate(polygon);

lucene/test-framework/src/java/org/apache/lucene/geo/GeoTestUtil.java

@@ -16,10 +16,17 @@
  */
 package org.apache.lucene.geo;
 
+import java.io.BufferedReader;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Random;
+import java.util.zip.GZIPInputStream;
 
 import org.apache.lucene.util.NumericUtils;
 import org.apache.lucene.util.SloppyMath;
@@ -718,4 +725,26 @@ public class GeoTestUtil {
     }
     return c;
   }
+
+  /** reads a shape from file */
+  public static String readShape(String name) throws IOException {
+    return Loader.LOADER.readShape(name);
+  }
+
+  private static class Loader {
+
+    static Loader LOADER = new Loader();
+
+    String readShape(String name) throws IOException {
+      InputStream is = getClass().getResourceAsStream(name);
+      if (is == null) {
+        throw new FileNotFoundException("classpath resource not found: " + name);
+      }
+      if (name.endsWith(".gz")) {
+        is = new GZIPInputStream(is);
+      }
+      BufferedReader reader = new BufferedReader(new InputStreamReader(is, StandardCharsets.UTF_8));
+      return reader.readLine();
+    }
+  }
 }