Date: Tue, 21 Mar 1995 03:06:37 -0400 (AST)
From: Bill Davidson <bdavidson AT ra DOT isisnet DOT com>
Subject: Debugging graphics programs
To: djgpp AT sun DOT soe DOT clarkson DOT edu

Hi:
Am I missing something here, or just lucky?
I keep reading messages about problems debugging programs in graphics 
mode.  At first I sympathized entirely since I was still using my old 
Hercules compatible card.  Lately though, I move into the nineties (or at 
least the eighties) and bought a SVGA card and monitor, the cheapest I 
could fine.  The card is a Trident 8900 variant.
Anyway, I ported some old graphics mode programs to djgpp, experienced 
some minor problems (you don't want to know...) and tried to debug them.  
I though maybe I could catch the problems before the program switched to 
graphics mode.  No luck, the error was after the mode switch.
BUT the debugger output was still there on the screen! (Using both gdb 
and edebug32.)  Sure, it trashed part of the graphics screen, but that 
seemed a small price to pay.  And yes, in 1024*768 mode I put a lot of 
nose-prints on the screen because the type was so small.  But there it 
was, right down to NPX dumps.
So what gives??  Again, am I just lucky and happened to buy the only SVGA 
card in the world that writes text to the screen in graphics mode, or am 
I missing something here???  I really would like to know, I am new to VGA 
and haven't even read up on it yet (any good book reccommendations?), and 
I am curious as to why this worked.  (Pretty weird, eh?  Writing to djgpp 
wondering why something worked!)
I have noted that my Trident card has two buffers, one for text mode and 
one for graphics mode.  Is this unusual?
Mystified but happy
Bill Davidson
bdavidson AT ra DOT isisnet DOT com