Newsgroups: comp.os.msdos.djgpp
From: tob AT world DOT std DOT com
Subject: Re: allegro quetion
Message-ID: <EF2H7w.9vw@world.std.com>
Sender: tob AT world DOT std DOT com (Tom Breton)
Reply-To: tob AT world DOT std DOT com
Organization: BREnterprises
References: <01bca9d7$9a404fa0$5bf141c2 AT liquid-machine>
Date: Sun, 17 Aug 1997 16:45:32 GMT
Lines: 39
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Precedence: bulk

"Filipe Marques de Almeida" <liquidk AT thepentagon DOT com> writes:
> sorry for the dumb question but i am kind of new to djgpp and allegro

It's not a dumb question, especially compared to another question I just
saw... }:)

> is there a problem of using something like this for memory bitmaps
>
> BITMAP *bitmap;
> unsigned char *map;
>
> map = bitmap->line[0];
>
> and then using map for accessing in a linear way.
>
> my question is:
> are the memory bitmaps always one chunk (like graph mode 0x13) or is there
> the danger of the bitmaps getting fragmented

Generally one chunk but not always.

Memory bitmaps (What you make with create_bitmap) will always AFAIK be a
single contiguous chunk. Screen bitmaps will depend on what mode you are
in. The standard VGA modes will be linear, AFAIK. Banked modes --
generally, any screen-size so big that you need SVGA to display it --
are not linear.

Shawn already provided some support for what you want. This function
will tell you what you want to know:

[From allegro.txt]
int is_linear_bitmap(BITMAP *bmp);
   Returns TRUE if bmp is a linear bitmap, ie. a memory bitmap, mode 13h 
   screen, or SVGA screen. Linear bitmaps can be used with the _putpixel(), 
   _getpixel(), bmp_write_line(), and bmp_read_line() functions.
[End inclusion from allegro.txt]

        Tom