🚀 go-pugleaf

johnw@wixer.cactus.org (john winthrop) writes:

 > There are two main reasons that os/2 doesn't support VGA (and SVGA)
 > modes in a window...
 > first, (s)vga modes  take up a lot of memory (up to 1 meg
 > generally, newer cards use even more memory).... To support
 > virtualized vga modes would mean that os/2 would have to have at
 > least that much memory available FOR EACH WINDOW! This would eat up
 > resources faster than godzilla could trample Tokyo.

With all due respect, I'm afraid I don't buy that argument.  The
shadow memory required for a standard VGA 640x480x16 graphics screen
is only 150Kb; for SVGA 800x600x16 it's only 235Kb.  True, it's easier
to shadow the entire video buffer, but it's not strictly necessary.
Even so, 256Kb, which is not a very big deal, is adequate to
virtualize standard VGA 640x480x16 graphics; i.e., 4 virtualized VGA
graphics applications would require a total of only 1Mb of shadow
memory.  ( yawn :)

In fact, OS/2 allocates a full shadow buffer of up to 1Mb for every
full-screen DOS application, so that it can save the display when that
application is switched to the background.  So the amount of shadow
memory is not really an important factor.

 > Second, most vga modes use bit planes.  For those not familiar with
 > bit planes, they are simply a mechanism for accessing more than one
 > byte of video memory at a time, by compromising on whether you want
 > to access one pixel color on the screen, or access a group of
 > pixels quickly.
 > One write to a bit plane could update several bytes of video
 > memory, which would recquire os/2 to modify those bytes in its own
 > bufffer.  The result would be the speed of the original apple ][...
 > Much of the success of vga is due to the fact that it is so quick
 > to do pixel writes and copies.

Again, with all due respect I don't buy that argument.  DESQview
virtualizes standard VGA 640x480x16 "bit plane" graphics in a window
or in the background with acceptable performance.  If DESQview can do
it, there's no reason OS/2 shouldn't be able to do at least as well.
Although 640x480x16 would certainly be enough to satisfy me,
supporting 800x600x16 wouldn't be all that much harder.

Best regards,
John
                                                                                       
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