Why don't the lines connect ?

Import mojo

Class Game Extends App
	'#################
	Method OnCreate () 
	'#################
		'Local mode:DisplayMode = DesktopMode()
		'SetDeviceWindow(mode.Width,mode.Height,1)
		SetDeviceWindow(640,480,1)
		SetUpdateRate 60
	End
	
	'#################
	Method OnUpdate () 
	'#################
		If KeyDown (KEY_ESCAPE) Then EndApp
	End
	
	'#################
	Method OnRender ()
	'#################
		Cls 0, 0, 0
		SetColor 255, 255, 255
		
		For Local y:Float = 0 To 479 Step 32
			For Local x:float = 0 To 639 Step 32 
				DrawLine x, y, x, y+31
				DrawLine x, y, x+31, y
				DrawLine x+31, y, x+31, y+31
				DrawLine x, y+31, x+31, y+31
			Next
		Next
	End
End

Function Main ()
	New Game
End