Date: Sun, 5 Oct 1997 22:31:15 -0700 (PDT)
Message-Id: <199710060531.WAA06446@adit.ap.net>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
To: "Alex Barsamian" <bigalex AT worldnet DOT att DOT net>, djgpp AT delorie DOT com
From: Nate Eldredge <eldredge AT ap DOT net>
Subject: Re: Yet another graphics problem...
Precedence: bulk

At 01:28  10/5/1997 -0600, Alex Barsamian wrote:
> I started out tonite porting my crusty mode 13h real mode graphics code out
>to djgpp.  I can init the graphics mode okay, even write to the screen
>without too much trouble.  Now for some reason when I began to implement the
>double buffer routines into the new source file, I compile without any
>trouble, but about 1/4 of the time, when I should be seeing a PCX image, I
>see a blank screen (in graphics mode), and the rest of the time I get a
>lovely page fault.
Have you tried symifying it? That's often helpful in finding crashes. Also,
fsdb can debug graphics programs, and IIRC so can RHGDB. Something else I
noticed follows.
[lots deleted]
>// get a pcx, skipping most unnecessary stuff that can be assumed
>// e.g., size (for now 640x480 pcx's are all i'll use, 8 bpp, etc.
>// I know this is far from portable but this is just to get this thing
>// rolling
>
>unsigned char *load_pcx(char *filename)
>{
[ /* ... deleted ... */ ]
>        width = -(getw(f));        /* xmin */
>        height = -(getw(f));       /* ymin */
>        width += getw(f) + 1;      /* xmax */
>        height += getw(f) + 1;     /* ymax */
I'm afraid I don't know what the PCX format is, but are you sure these are
supposed to be 32-bit values? getw reads an int, which is 32 bits on DJGPP,
but 16 on most other DOS compilers. If they *are* 16-bit values, use fread
and a `short'. That could be a porting issue that slipped by. If I'm wrong,
sorry for giving bad advice :)


Nate Eldredge
eldredge AT ap DOT net