region: add 'path' query for segments

cruft/util/region.hpp

@@ -370,6 +370,26 @@ namespace cruft {
     rotate90 (cruft::region2<T> obj, int steps);
 
 
+    ///////////////////////////////////////////////////////////////////////////
+    /// Returns the vertices of the region (excluding last->first vertex) in
+    /// CCW winding.
+    ///
+    /// It assumes the base position is the min / extent is strictly positive.
+    template <typename T>
+    std::array<cruft::point2<T>, 4>
+    path (cruft::region2<T> const &obj)
+    {
+        CHECK (all (obj.e > 0));
+
+        return {
+            obj.p,
+            obj.p + vector2<T> {      0, obj.e.h },
+            obj.p + vector2<T> {obj.e.w, obj.e.h },
+            obj.p + vector2<T> {obj.e.w,       0 },
+        };
+    }
+
+
     ///////////////////////////////////////////////////////////////////////////
     template <size_t S, typename T>
     std::ostream& operator<< (std::ostream&, const cruft::region<S,T>&);

test/region.cpp

@@ -286,5 +286,31 @@ main (int, char **)
         }
     }
 
+    // Test that 'path' returns expected values
+    {
+        //  (-5, 3)   (1, 3)
+        //
+        //
+        //  (-5,-4)*  (1,-4)
+        //
+        //  Start at the bottom right corner.
+
+        cruft::region2i const shape {
+            cruft::point2i { -5, -4, },
+            cruft::point2i {  1,  3, },
+        };
+
+        cruft::point2i const expected[] = {
+            cruft::point2i {  -5, -4  },
+            cruft::point2i {  -5,  3  },
+            cruft::point2i {   1,  3  },
+            cruft::point2i {   1, -4  },
+        };
+
+        auto const computed = path (shape);
+
+        tap.expect (std::ranges::equal (computed, expected), "region2i path");
+    }
+
     return tap.status ();
 }