added scenes/subtract-subtract.fart (illustrating bug) and updated .todo

git-svn-id: svn://anubis/fart/trunk@197 7f9b0f55-74a9-4bce-be96-3c2cd072584d

.todo

@@ -1,3 +1,5 @@
 FART To-Do List
 ===============
-- Test subtractions of subtractions
+- Fix subtractions of subtractions (inverting normals problem)
+- Shape definitions / reusability
+- Add distribution infrastructure

scenes/subtract-subtract.fart

@@ -0,0 +1,44 @@
+
+scene
+{
+    options
+    {
+        multisample 2
+    }
+
+    camera
+    {
+        position <1, -2, 1>
+        look_at <0, 0, 0>
+    }
+
+    light
+    {
+        position <-1, -3, 4>
+    }
+
+    subtract
+    {
+        box
+        {
+            size <1, 1, 1>
+            material { color <0.2, 0.2, 1> }
+        }
+
+        subtract
+        {
+            sphere
+            {
+                radius 0.4
+                material { color <1, 0, 0> }
+                translate <0, -0.5, 0>
+            }
+            box
+            {
+                size <1, 1, 0.2>
+                material { color <0, 1, 0> }
+                translate <0, -0.5, 0>
+            }
+        }
+    }
+}