Windows dos box problem
Matthew Kroll
Ok, I run a dos app in a windows dos box which is in full screen mode,
in it, I have text which is blinking (character attribute 5 I think) no
problems.. Hit the Alt-Enter and put the dos box in windowed mode and
voila, my blinking character stops blinking and goes into a kind of
reverse video mode instead.. My only explanation for this is that when
in dos mode it writes to screen memory at 0B00H (or whatever it is) for
cga type video mode, and when windowed, the windows OS interprets what
goes there and instead rewrites it to the vga memory location
(incorrectly interpreted obviously).. Can someone please tell me that I
am wrong so that I may fix this somehow.
Thanks in advance, Matthew.
Lance Edmonds
When running a DOS (or Console) app in a window, what you see is how
Windows thinks it should look. Because flashing in a window would
require that Windows draw the text, wait, then clear it, wait, then
redraw the text (ad infinitum), and the fact that Windows cannot
guarantee that it is available to provide the flashing emulation at
precise intervals (Windows is often busy doing other things behind the
scenes like task switching, file serving, background applications,
etc), at best you'd get a poor flashing effect that varied wildly in
speed.
No only that, but it would be a poor use of the processor time, so
Microsoft decided not to provide functionality to emulate the effect.
What you usually get is not "reverse video", but a set of
high-intensity colors. This can be made available in full-screen mode
with the appropriate interrupt call too (I dont have the code handy to
do this, but I seem to recall seeing it in the ABC packets...
www.basicguru.com/abc
Another "sideeffect" of the implementation of windowed mode is
graphics... Windows either switches the app into full-screen mode, or
the app appears to freeze or look completely wrong. FOlks who use
graphical fonts or remap the font table also run into problems.
Essentially, there is one rule for this problem: "Some applications
must only be run in full-screen mode to work as intended".
To switch your app into full screen mode, use the following code (This
is PB/DOS code)
! push DS
! mov AX,&H168B
! xor BX,BX
! int &H2F
! pop DS
HTH,
Lance