add class function and geom.square constructor

2 files changed, 57 insertions, 5 deletions

diff --git a/city/geometry-test.lua b/city/geometry-test.lua
index ab3265d..3fedae6 100644
--- a/city/geometry-test.lua
+++ b/city/geometry-test.lua
@@ -1,6 +1,13 @@
 local test = require('minunit').test
 local geom = require 'geometry'
 
+
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+--
+-- geom.point tests
+--
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
 test(
    'create point object',
    function()
@@ -22,3 +29,25 @@ test(
       assert(a:distance_to(a) == 0)
    end
 )
+
+
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+--
+-- geom.square tests
+--
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+test(
+   'create square object',
+   function()
+      local s = geom.square(geom.point(0, 0), 1)
+      assert(s.center.x == 0)
+      assert(s.center.y == 0)
+      assert(s.span == 1)
+
+      assert(s.x.min == -0.5)
+      assert(s.x.max ==  0.5)
+      assert(s.y.min == -0.5)
+      assert(s.y.max ==  0.5)
+   end
+)
diff --git a/city/geometry.lua b/city/geometry.lua
index 47e6a78..a775213 100644
--- a/city/geometry.lua
+++ b/city/geometry.lua
@@ -1,17 +1,22 @@
 local geom = {}
 
+local function class(tbl)
+   setmetatable(tbl, tbl)
+   return tbl
+end
+
 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 --
 -- point
 --
 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-local point = {
-   __call = function(_, x, y)
+geom.point = class{
+   __call = function(this, x, y)
       local pt = {}
       pt.x = x
       pt.y = y
-      setmetatable(pt, {__index=_})
+      setmetatable(pt, {__index=this})
       return pt
    end,
 
@@ -21,8 +26,26 @@ local point = {
       return math.sqrt(d_x*d_x + d_y*d_y)
    end,
 }
-setmetatable(point, point)
-geom.point = point
 
 
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+--
+-- square
+--
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+geom.square = class{
+   __call = function(this, center, span)
+      local square = {}
+      square.center = center
+      square.span = span
+      square.x = this.axis_range(center.x, span/2)
+      square.y = this.axis_range(center.y, span/2)
+      setmetatable(square, {__index=this})
+      return square
+   end,
+
+   axis_range = function(c, r) return {min=c-r, max=c+r} end,
+}
+
 return geom