Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!samsung!think!mintaka!ogicse!cs.uoregon.edu!oregon!milton!max!8324155
From: 8324155@max.u.washington.edu
Newsgroups: comp.sys.ibm.pc.programmer
Subject: VGA smooth scrolling problem
Message-ID: <13409.25f447ea@max.u.washington.edu>
Date: 7 Mar 90 07:29:46 GMT
Organization: University of Washington, Seattle WA
Lines: 20


  Hi, I'm hoping someone can help me with this problem.
 
  I am trying to write an assembly routine which smoothly scrolls (one
pixel at a time) a VGA text screen.  I use the Preset Row Scan Register
(port 3d4h/3d5h, index 08h) to scroll the screen up one pixel at a time.
When I have scrolled the height of one full character (16 pixels in this
case) I reset the register, and then move the data up one line as fast as
possible (using the movsw command to move the data in video memory directly)
This works well up to a point.  The screen scrolls fine until a full
character has been scrolled.  At that point there is a slight flicker as the
register is reset and the data moved.  I have tried waiting for the video
refresh to finish by watching the status register bit 3 (port 3dah) and
then reseting the register and moving the screen, but this does not solve
the problem.  I would really appreciate any suggestions.
 
  Thanks,
 Mark