Program CohenSutherlandClipping

	Define ABOVE	As Integer = 8 // Set Bit 4
	Define BELOW	As Integer = 4 // Set Bit 3
	Define RIGHT	As Integer = 2 // Set Bit 2
	Define LEFT		As Integer = 1 // Set Bit 1
	
	Define Outside	As Boolean
	Define test As BitFiddle  // test addition to surface library, "And_"...
	

	 // Create some lines and clipp it
	Method Main()

		SetScreenSize( 640, 480 )
		
		Define Box As Rectangle
		Box.Color = DarkBlue
		Box.X = 100
		Box.Y = 100
		Box.Width = 440
		Box.Height = 280
		
		Define MyLine As Line
		Define Counter As Integer
		
		While Not IsKeyDown( Escape )
			Counter = 0
			ClearBackground( Black )
	
			While Counter < 50
				MyLine.StartPoint.X = Random( 10, ScreenWidth()-20)
				MyLine.StartPoint.Y = Random( 10, ScreenHeight()-20)
				MyLine.EndPoint.X = Random( 10, ScreenWidth()-20)
				MyLine.EndPoint.Y = Random( 10, ScreenHeight()-20)
				MyLine.Color = Red
				MyLine.Draw()
				Box.Draw()
				ClipLine( Box, MyLine )
				If Not Outside Then
					MyLine.Color = Yellow
					MyLine.Draw()
					Box.Draw()
				End If
				Delay( 300 )
				Counter = Counter + 1
			End While
		End While

	End Method
	
	Function ClipLine( Box As Rectangle, ClipLine As Line ) As Line
		
		Define Code1	As Integer
		Define Code2	As Integer
		
		Define Dx As Decimal = ClipLine.EndPoint.X - ClipLine.StartPoint.X
		Define Dy As Decimal = ClipLine.EndPoint.Y - ClipLine.StartPoint.Y
		
		Define Done	As Boolean = False
		
		While Not Done
			Code1 = FindRegion( Box, ClipLine.StartPoint )
			Code2 = FindRegion( Box, ClipLine.EndPoint )
			
			If TEST.OR_( Code1, Code2 ) = 0 Then // Line is in Box
				Outside = False
				Return ClipLine
				
			Else If Test.And_( Code1, Code2 ) <> 0 Then // Line is Complete outside
				Outside = True
				Return ClipLine
				
			Else If Test.And_( Code1, LEFT ) = LEFT Then // Startpoint is left out
				ClipLine.StartPoint.Y = ClipLine.StartPoint.Y + ( Box.Left - ClipLine.StartPoint.X ) * Dy / Dx
				ClipLine.StartPoint.X = Box.Left
				
			Else If Test.And_( Code2, LEFT ) = LEFT Then // Endpoint is left out
				ClipLine.EndPoint.Y = ClipLine.EndPoint.Y + ( Box.Left - ClipLine.EndPoint.X ) * Dy / Dx
				ClipLine.EndPoint.X = Box.Left
				
			Else If Test.And_( Code1, RIGHT ) = RIGHT Then // Startpoint is right out
				ClipLine.StartPoint.Y = ClipLine.StartPoint.Y + ( Box.Right - ClipLine.StartPoint.X ) * Dy / Dx
				ClipLine.StartPoint.X = Box.Right
				
			Else If Test.And_( Code2, RIGHT ) = RIGHT Then // Endpoint is right out
				ClipLine.EndPoint.Y = ClipLine.EndPoint.Y + ( Box.Right - ClipLine.EndPoint.X ) * Dy / Dx
				ClipLine.EndPoint.X = Box.Right
				
			Else If Test.And_( Code1, BELOW ) = BELOW Then // Startpoint is below out
				ClipLine.StartPoint.X = ClipLine.StartPoint.X + ( Box.Bottom - ClipLine.StartPoint.Y ) * Dx / Dy
				ClipLine.StartPoint.Y = Box.Bottom
				
			Else If Test.And_( Code2, BELOW ) = BELOW Then // Endpoint is below out
				ClipLine.EndPoint.X = ClipLine.EndPoint.X + ( Box.Bottom - ClipLine.EndPoint.Y ) * Dx / Dy
				ClipLine.EndPoint.Y = Box.Bottom
				
			Else If Test.And_( Code1, ABOVE ) = ABOVE Then // Startpoint is above out
				ClipLine.StartPoint.X = ClipLine.StartPoint.X + ( Box.Top - ClipLine.StartPoint.Y ) * Dx / Dy
				ClipLine.StartPoint.Y = Box.Top
				
			Else If Test.And_( Code2, ABOVE ) = ABOVE Then // Endpoint is above out
				ClipLine.EndPoint.X = ClipLine.EndPoint.X + ( Box.Top - ClipLine.EndPoint.Y ) * Dx / Dy
				ClipLine.EndPoint.Y = Box.Top
				
			End If
		
		End While
		
		Return ClipLine
	End Function
	
	Function FindRegion( Box As Rectangle, ClipPoint As Point ) As Integer
		Define Code As Integer = 0
		
		If ClipPoint.X < Box.Left Then
			Code = Code + LEFT
		Else If ClipPoint.X > Box.Right Then
			Code = Code + RIGHT
		End If
			
		If ClipPoint.Y < Box.Top Then
			Code = Code + ABOVE
		Else If ClipPoint.Y > Box.Bottom Then
			Code = Code + BELOW
		End If
		
		Return Code
	End Function	

	// --------------------------------------------------------------
	//   1 OR 1 = 1
	//   1 OR 0 = 1
	//   0 OR 1 = 1
	//   0 OR 0 = 0
	// --------------------------------------------------------------
	Function OR_( a As Integer, b As Integer ) As Integer
		Define a1	As Integer
		Define b1	As Integer
		Define c	As Integer = 0
		Define d	As Integer = 1
		While Not ( a = 0 And b = 0 )
			a1 = a
			a  = a / 2
			b1 = b
			b  = b / 2
			If a1 <> a + a Or b1 <> b + b Then
				c = c + d
			End If
			d = d + d
		End While
		Return c
	End Function
	
	// --------------------------------------------------------------
	//   1 AND 1 = 1
	//   1 AND 0 = 0
	//   0 AND 1 = 0
	//   0 AND 0 = 0
	// --------------------------------------------------------------
	Function AND_( a As Integer, b As Integer ) As Integer
		Define a1	As Integer
		Define b1	As Integer
		Define c	As Integer = 0
		Define d	As Integer = 1
		While Not ( a = 0 Or b = 0 )
			a1 = a
			a  = a / 2
			b1 = b
			b  = b / 2
			If a1 <> a + a And b1 <> b + b Then
				c = c + d
			End If
			d = d + d
		End While
		Return c
	End Function

	// --------------------------------------------------------------
	//   1 EOR 1 = 0
	//   1 EOR 0 = 1
	//   0 EOR 1 = 1
	//   0 EOR 0 = 0
	// --------------------------------------------------------------
	Function EOR_( a As Integer, b As Integer ) As Integer
		Define a1	As Integer
		Define b1	As Integer
		Define c	As Integer = 0
		Define d	As Integer = 1
		While Not ( a = 0 And b = 0 )
			a1 = a
			a  = a / 2
			b1 = b
			b  = b / 2
			If ( a1 <> a + a And b1 = b + b ) Or ( a1 = a + a And b1 <> b + b ) Then
				c = c + d
			End If
			d = d + d
		End While
		Return c
	End Function
	
End Program