Fix intersecting linestrings

This commit fixes an issue where fully contained linestrings are not intersecting. Fixes #3
tidwall · Sep 25, 2023 · b0af7c4 · b0af7c4
1 parent 57ed66b
commit b0af7c4
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Showing 2 changed files with 64 additions and 2 deletions.
diff --git a/tests/relations/line.jsonc b/tests/relations/line.jsonc
@@ -378,5 +378,65 @@
       "overlaps":   ["F", "F"],
       "touches":    ["F", "F"]
     }
+  },
+  {
+    "geoms": [
+      "LINESTRING(1 0, 2 0)",
+      "LINESTRING(0 0,3 0)"
+    ],
+    "dims": [ 1, 1 ],
+    "relate": [ "1FF0FF102", "101FF0FF2" ],
+    "predicates": {
+      "equals":     ["F", "F"],
+      "intersects": ["T", "T"],
+      "disjoint":   ["F", "F"],
+      "contains":   ["F", "T"],
+      "within":     ["T", "F"],
+      "covers":     ["F", "T"],
+      "coveredby":  ["T", "F"],
+      "crosses":    ["F", "F"],
+      "overlaps":   ["F", "F"],
+      "touches":    ["F", "F"]
+    }
+  },
+  {
+    "geoms": [
+      "LINESTRING(1 1,2 2)",
+      "LINESTRING(0 0,3 3)"
+    ],
+    "dims": [ 1, 1 ],
+    "relate": [ "1FF0FF102", "101FF0FF2" ],
+    "predicates": {
+      "equals":     ["F", "F"],
+      "intersects": ["T", "T"],
+      "disjoint":   ["F", "F"],
+      "contains":   ["F", "T"],
+      "within":     ["T", "F"],
+      "covers":     ["F", "T"],
+      "coveredby":  ["T", "F"],
+      "crosses":    ["F", "F"],
+      "overlaps":   ["F", "F"],
+      "touches":    ["F", "F"]
+    }
+  },
+  {
+    "geoms": [
+      "LINESTRING(-0.5 0.5,-0.1 0.1)",
+      "LINESTRING(-1 1,1 -1)"
+    ],
+    "dims": [ 1, 1 ],
+    "relate": [ "1FF0FF102", "101FF0FF2" ],
+    "predicates": {
+      "equals":     ["F", "F"],
+      "intersects": ["T", "T"],
+      "disjoint":   ["F", "F"],
+      "contains":   ["F", "T"],
+      "within":     ["T", "F"],
+      "covers":     ["F", "T"],
+      "coveredby":  ["T", "F"],
+      "crosses":    ["F", "F"],
+      "overlaps":   ["F", "F"],
+      "touches":    ["F", "F"]
+    }
   }
 ]
diff --git a/tg.c b/tg.c
@@ -947,8 +947,10 @@ bool tg_segment_intersects_segment(struct tg_segment seg_a,
         if (!(((c.x-a.x <= 0) != (c.x-b.x <= 0))) ||
               ((c.y-a.y <= 0) != (c.y-b.y <= 0)))
         {
-            return (tg_segment_covers_point(seg_a, seg_b.a) || 
-                    tg_segment_covers_point(seg_a, seg_b.b));
+            return tg_segment_covers_point(seg_a, seg_b.a) || 
+                   tg_segment_covers_point(seg_a, seg_b.b) ||
+                   tg_segment_covers_point(seg_b, seg_a.a) ||
+                   tg_segment_covers_point(seg_b, seg_a.b);
         }
         return true;
     }