okay... another test program "copper" by Surprise! production. I finally
figured out what the demo meant by "making the screen wobble", and God
is it awful. All along I thought it was playing with the hpel register
in the Attribute Controller. Some quick debugging shows that the
"sinuswobble" is actually done by playing with the Start Horizontal
Retrace register per scanline---ACK! I wonder to this day if such a demo
effect has shortened the life of anyone's VGA monitor. Also noted is
that such a demo effect would NEVER work on today's scan converters and
LCD flat panel monitors, because modern monitors look for changes in
hsync/vsync pulses to detect mode changes. Added code alongside hpel
wobble emulation, so that you can enable emulation of the effect. If
enabled, changes in the Start Horizontal Retrace register are used to
displace the scanline to emulate the visual effect, which allows the
sinuswobble in the demo to work correctly.