'===========================================================================
' Subject: MODE-X SCROLL                     Date: Unknown Date           
' Author:  Jason Plackey                     Code: QB, QBasic, PDS        
' Origin:  Prodigy                         Packet: GRAPHICS.ABC
'===========================================================================
'  Regarding the example code...  Change the delay% value to
'accommodate your CPU's speed.  The TIMER function is
'relatively inaccurate when dealing with fractions of a
'second, and I had insufficient space to include my own timer
'routine.
'       
'  If you have any questions, feel free to ask.
'Happy coding!     Jason Plackey

DECLARE SUB ModeX ()
DECLARE SUB OutPort (PortAddr&, vh%, vl%)
DECLARE SUB Standard ()
DECLARE SUB SetVOffset (Offset&)
                                                           
SCREEN 13: DEF SEG = &HA000: CALL ModeX
                                                           
FOR count% = 0 TO 63
  redval& = count%
  greenval& = 256 * count%
  blueval& = 65536 * count%
  rgbval& = blueval& + greenval& + redval&
  PALETTE count%, redval&
  PALETTE count% + 64, greenval&
  PALETTE count% + 128, blueval&
  PALETTE count% + 192, rgbval&
NEXT count%
                                                           
FOR Offset& = 0 TO 15999
  rgbbase% = Offset& MOD 64
  POKE Offset&, rgbbase%
  POKE Offset& + 16000, rgbbase% + 64
  POKE Offset& + 32000, rgbbase% + 128
  POKE Offset& + 48000, rgbbase% + 192
NEXT Offset&
                                            
Offset& = 0: OffsetInc% = 80: Frame% = 0
                                                    
DO
  Offset& = Offset& + OffsetInc%
  CALL SetVOffset(Offset&): WAIT &H3DA, 8
  Frame% = Frame% + 1
    IF Frame% = 99 THEN OffsetInc% = 81
    IF Frame% = 199 THEN OffsetInc% = 79
    IF Frame% = 299 THEN OffsetInc% = 80
    IF Frame% = 499 THEN OffsetInc% = -80
    IF Frame% = 599 THEN OffsetInc% = -79
    IF Frame% = 699 THEN OffsetInc% = -81
    IF Frame% = 799 THEN OffsetInc% = -80
    IF Frame% = 899 THEN
      CLS : PALETTE
      CALL SetVOffset(0): CALL Standard
      END
    END IF
  FOR delay% = 1 TO 1000: NEXT delay%
LOOP

SUB ModeX
  CALL OutPort(&H3C4, 6, 4): CLS
  CALL OutPort(&H3D4, 227, 23)
  CALL OutPort(&H3D4, 0, 20)
  CALL OutPort(&H3C4, 15, 2)
END SUB

SUB OutPort (PortAddr&, vh%, vl%)
  OUT PortAddr&, vl%: OUT PortAddr& + 1, vh%
END SUB

SUB SetVOffset (Offset&)
  V& = Offset&
  CALL OutPort(&H3D4, V& \ 256, 12)
  CALL OutPort(&H3D4, V& AND 255, 13)
END SUB

SUB Standard
  CALL OutPort(&H3C4, 14, 4)
  CALL OutPort(&H3D4, 163, &H17)
  CALL OutPort(&H3D4, 64, &H14)
  CALL OutPort(&H3C4, 15, &H2)
END SUB