1 files changed, 14 insertions, 0 deletions
diff --git a/city/geometry.lua b/city/geometry.lua
index e380173..410b4a3 100644
--- a/city/geometry.lua
+++ b/city/geometry.lua
@@ -169,6 +169,20 @@ geom.qt_node = class{
       for _, child in ipairs(self.children) do
 	 child:query(region, points)
       end
+   end,
+
+   -- return the leaf node containing the given point
+   -- returns nil if no such node exists (i.e. the point
+   -- is out of bounds)
+   find_containing = function(self, point)
+      if not self.square:contains(point) then return end
+
+      if self:is_leaf() then return self end
+
+      for _, child in ipairs(self.children) do
+	 local result = child:find_containing(point)
+	 if result then return result end
+      end
    end
 }