Major updates

tile_grid.py

@@ -1,4 +1,11 @@
+# tile_grid.py
+# ------------
+# By MWC Contributors
+#
+# Implements `draw_tile_grid`, which draws a grid of tiles. 
+
 from turtle import *
+from tile import fly
 
 def draw_tile_grid(width, height, tile_size, tile_function):
     """Draws a (width x height) grid, with tile_function drawn on each tile.
@@ -8,32 +15,26 @@ def draw_tile_grid(width, height, tile_size, tile_function):
     for y in range(height):
         for x in range(width):
             tile_function(tile_size)
-            forward(tile_size)
+            fly(tile_size)
         return_to_x_origin(tile_size, width)
         move_up_one_row(tile_size)
     return_to_y_origin(tile_size, height)
 
 def return_to_x_origin(tile_size, width):
     "After drawing a row of tiles, returns the turtle to the starting x position"
-    penup()
-    back(tile_size * width)
-    pendown()
+    fly(-1 * tile_size * width)
 
 def return_to_y_origin(tile_size, height):
     "After drawing all rows of tiles, returns the turtle to the starting y position"
-    penup()
     right(90)
-    forward(tile_size * height)
+    fly(tile_size * height)
     left(90)
-    pendown()
 
 def move_up_one_row(tile_size):
     "Moves the turtle up one row"
-    penup()
     left(90)
-    forward(tile_size)
+    fly(tile_size)
     right(90)
-    pendown()