engine: Reposition functions

These functions can set GameObjects on the edges of their boundaries or
in the middle of the boundary region.

Additionally, movement in the x or y direction should be through the
closest integer and not a float (because pygame rects only work for
integers)

engine/object.py

@@ -24,7 +24,7 @@ class GameObject:
 		self.max_y = h - self.h
 
 	def move_x(self, do_move, ms):
-		dx = do_move * self.dx * ms
+		dx = int(do_move * self.dx * ms)
 		self.x += dx
 		if self.allow_offscreen == False:
 			if self.x < self.min_x:
@@ -34,7 +34,7 @@ class GameObject:
 		self.rect.move_ip(dx, 0)
 
 	def move_y(self, do_move, ms):
-		dy = do_move * self.dy * ms
+		dy = int(do_move * self.dy * ms)
 		self.y += dy
 		if self.allow_offscreen == False:
 			if self.y < self.min_y:
@@ -50,6 +50,24 @@ class GameObject:
 		self.y = y
 		self.rect.move_ip(dx, dy)
 
+	def center_x(self):
+		self.reposition(self.max_x / 2, self.y)
+
+	def left_x(self):
+		self.reposition(0, self.y)
+
+	def right_x(self):
+		self.reposition(self.max_x, self.y)
+
+	def center_y(self):
+		self.reposition(self.x, self.max_y / 2)
+
+	def top_y(self):
+		self.reposition(self.x, 0)
+
+	def bottom_y(self):
+		self.reposition(self.x, self.max_y)
+
 	def is_offscreen(self):
 		if self.allow_offscreen == False:
 			return False

games/spaceblaster/arcade.py

@@ -18,7 +18,9 @@ B     = pygame.K_b
 
 class ArcadeState(games.GameState):
 	def __init__(self, GAME):
-		self.ship  = ship.CSE1670(GAME, (10, 10), (0.25, 0.25))
+		self.ship  = ship.CSE1670(GAME, (0.25, 0.25))
+		self.ship.center_x()
+		self.ship.bottom_y()
 		self.stars = tiled_image(GAME, "stars.png")
 		self.fire_interval = 100
 		self.beams   = []

games/spaceblaster/ship.py

@@ -24,8 +24,8 @@ class ArcadeShip(GO):
 
 
 class CSE1670(ArcadeShip):
-	def __init__(self, GAME, pos, speed):
-		ArcadeShip.__init__(self, GAME, "cse_1670.png", pos, speed)
+	def __init__(self, GAME, speed):
+		ArcadeShip.__init__(self, GAME, "cse_1670.png", (0, 0), speed)
 		self.game         = GAME
 		self.weapon_level = 0