add square:divide() function

1 files changed, 20 insertions, 0 deletions

diff --git a/city/geometry.lua b/city/geometry.lua
index 1632393..13088d1 100644
--- a/city/geometry.lua
+++ b/city/geometry.lua
@@ -47,6 +47,9 @@ geom.square = class{
 
    axis_range = function(c, r) return {min=c-r, max=c+r} end,
 
+   -- returns true if a point is inside of the square
+   -- and false otherwise
+   -- (x/y mininum exclusive, maximum inclusive)
    contains = function(self, point)
       local x_overlap =
 	 (point.x > self.x.min) and (point.x <= self.x.max)
@@ -57,6 +60,23 @@ geom.square = class{
 	 return true
       end
       return false
+   end,
+
+   -- return an array of four squares covering the same
+   -- area as their parent
+   divide = function(self)
+      local this = getmetatable(self).__index
+      
+      local x = self.center.x
+      local y = self.center.y
+      local d = self.span / 4
+      
+      return {
+	 this(geom.point(x-d, y-d), d*2),
+	 this(geom.point(x+d, y-d), d*2),
+	 this(geom.point(x-d, y+d), d*2),
+	 this(geom.point(x+d, y+d), d*2),
+      }
    end
 }