From: Shawn Hargreaves <Shawn AT talula DOT demon DOT co DOT uk>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Problems With Displaying Graphics
Date: Thu, 29 May 1997 19:12:51 +0100
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Michael M. writes:
>I am having problems displaying a graphic with the Allegro 2.2 library.
>Whenever I try to run this, it just shows a blank, black screen; or
>sometimes it has a SIGSEGV error.  I compile it with the command line:
[snip]
>void main(int argc, char *argv[])
>{
>   BITMAP *buffer;
>   PALLETE the_pallete;
>
>   start_up();                 // Initilizes Allegro,keyboard,timer,mouse
>   display_copyright();                // Displays my name

What are these functions? When posting code, please try to get it into a
state that I can compile myself. If I can't run it, I can't so easily
see where it might be going wrong... 

>   set_gfx_mode(GFX_AUTODETECT, 640, 480, 0, 0);     // SVGA mode

You should check the return value from this function: it can fail! If
Allegro is unable to set the requested mode, you should check and give
an error message, not just go on as if everything was ok...

>   buffer = create_bitmap(50,50);      // Creates a 50 by 50 bitmap
>   clear(buffer);                      // Clears newly made bitmap
>   buffer = load_bitmap(argv[1], the_pallete); //loads the file into buffer

Again, check the return code from load_bitmap(). It might not succeed!

Also, you don't need to do the create_bitmap() before loading the image.
Just load_bitmap() alone is enough, because it allocates whatever
storage it needs. Look at examples\ex15.c...

My guess is that either the set_gfx_mode() or load_bitmap() calls are
failing. Probably the load_bitmap(), if your PCX file isn't in the
correct format...


--
Shawn Hargreaves - shawn AT talula DOT demon DOT co DOT uk - http://www.talula.demon.co.uk/
Beauty is a French phonetic corruption of a short cloth neck ornament.