veiwport help required

ok, i've kind of got this working now, but it's a little clunky when you move into the corners. anyone know why?

SuperStrict
Graphics 800, 600, 32, 60

Local p1:player = New player.Create()
p1.x = 1000;p1.y = 900

While Not KeyHit(KEY_ESCAPE)
'top left
	If p1.x - p1.dx <= 400 And p1.y - p1.dy <= 300
		SetOrigin 0, 0
		SetViewport 0 - p1.x, 0 - p1.y, 1600, 1200
'bottom Right
	Else If p1.x - p1.dx <= 400 And p1.y + p1.dy >= 900
		SetOrigin 0, 600 - (1200 - p1.y) - p1.y
		SetViewport 0 - p1.x, 600 - p1.y, 1600, 1200
'bottom left	
	ElseIf p1.x + p1.dx >= 1200 And p1.y + p1.dy >= 900
		SetOrigin 800 - (1600 - p1.x) - p1.x, 600 - (1200 - p1.y) - p1.y
		SetViewport 800 - p1.x, 600 - p1.y, 1600, 1200
'top right	
	Else If p1.x + p1.dx >= 1200 And p1.y - p1.dy <= 300
		SetOrigin 800 - (1600 - p1.x) - p1.x, 0
		SetViewport 800 - p1.x, 0 - p1.y, 1600, 1200
'right edge
    ElseIf p1.x + p1.dx >= 1200
		SetOrigin 800 - (1600 - p1.x) - p1.x, 300 - p1.y
		SetViewport 800 - p1.x, 300 - p1.y, 1600, 1200
'bottom edge
	Else If p1.y + p1.dy >= 900
		SetOrigin 400 - p1.x, 600 - (1200 - p1.y) - p1.y
		SetViewport 400 - p1.x, 600 - p1.y, 1600, 1200
'Left edge
	ElseIf p1.x - p1.dx <= 400
		SetOrigin 0, 300 - p1.y
		SetViewport 0 - p1.x, 300 - p1.y, 1600, 1200
'top edge
	Else If p1.y - p1.dy <= 300
		SetOrigin 400 - p1.x, 0
		SetViewport 400 - p1.x, 0 - p1.y, 1600, 1200
	Else
'middle
	SetOrigin 400 - p1.x, 300 - p1.y
	SetViewport 400 - p1.x, 300 - p1.y, 1600, 1200
	End If

'draw background	
	For Local i:Int = 0 To 5
		For Local o:Int = 0 To 7
			If i Mod 2 = 0
				If o Mod 2 = 0
					SetColor 0, 0, 0
				Else
					SetColor 255, 255, 255
				End If
			Else
				If o Mod 2 = 0
					SetColor 255, 255, 255
				Else
					SetColor 0, 0, 0
				End If
			End If
			
			DrawRect (o * 200) , (i * 200), 200, 200
			'SetColor 255, 255, 255
			'DrawText ((o * 200) + " " + (i * 200)), (o * 200) , (i * 200)
		Next
	Next

'draw player
	p1.update()
	p1.draw()
	
	Flip
	Cls
Wend

Type player

	Field easing:Float = 0.10;
	Field dx:Float;
	Field dy:Float;
	Field x:Float
	Field y:Float

	Function Create:player()
		Local n:player = New player;
		Return n;
	End Function
	
	Method update() 
			
		Local mx:Int = MouseX() * 2
		Local my:Int = MouseY() * 2
   		
		dx = mx - x;
   		dy = my - y;
   
  	 	dx:*easing:Float;
   		dy:*easing;
   
   		x:+dx;
   		y:+dy;
		
	End Method
   
	Method draw() 
		SetColor 0, 0, 255
		DrawRect x, y, 10, 10
	End Method
	
End Type

cheers
Charlie