From:	Einar <"eincar"@[EINAR]vip.cybercity.dk>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Retrieving BMP from datafile?
Date:	Sun, 23 Aug 1998 11:30:30 +0200
Organization:	CyberCity Internet
Lines:	112
Message-ID:	<6ron2n$rvh$1@news.cybercity.dk>
References:	<6r776u$snn$1 AT news DOT cybercity DOT dk>
NNTP-Posting-Host:	212.242.3.204
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To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Thanks for the help I've gotten on this question.

I now able to get the BMP files out of the data file with a warying
degree of success, that leaves me puzzled.
In the following lines I'll show you two examples of the same code, that
gives hugely different results. 

///////////// First example of my test program ///////////////

#include <allegro.h>
#include "othello.h"

DATAFILE *datafile;
BITMAP *back, *player1;
RGB *palette;

int main()
{
 allegro_init();
 install_keyboard();

 datafile=load_datafile("data.dat");
 set_palette((RGB*)datafile[othello].dat);
 set_gfx_mode(GFX_AUTODETECT,640,480,0,0);

 back=(BITMAP*)datafile[backgr].dat;
 player1=(BITMAP*)datafile[black].dat;
 blit(back,screen,0,0,0,0,back->w,back->h);
 readkey();
 clear(screen);
 blit(player1,screen,0,0,0,0,player1->w,player1->h);
 readkey();
 allegro_exit();
 destroy_bitmap(back);
 destroy_bitmap(player1);
 return 0;
}

This example worked fine, with the exception that the color scheme of
the BMP pictures where wrong.

//////////// Second example of my test program ///////////////

Here I've changed the second BITMAP variable player1 to black.

#include <allegro.h>
#include "othello.h"

DATAFILE *datafile;
BITMAP *back, *black;
RGB *palette;

int main()
{
 allegro_init();
 install_keyboard();

 datafile=load_datafile("data.dat");
 set_palette((RGB*)datafile[othello].dat);
 set_gfx_mode(GFX_AUTODETECT,640,480,0,0);

 back=(BITMAP*)datafile[backgr].dat;
 black=(BITMAP*)datafile[black].dat;
 blit(back,screen,0,0,0,0,back->w,back->h);
 readkey();
 clear(screen);
 blit(black,screen,0,0,0,0,black->w,black->h);
 readkey();
 allegro_exit();
 destroy_bitmap(back);
 destroy_bitmap(black);
 return 0;
}

And this change seems to create havoc inside the program, here are the
error messages I get when trying to compile the program:

Compiling: test.cc
test.cc (7) Error: parse error before `1'
In function `int main()':
test.cc (20) Error: non-lvalue in assignment
test.cc (24) Error: base operand of `->' is not a pointer
test.cc (24) Error: base operand of `->' is not a pointer
test.cc (24) Warning: passing `int' to argument 1 of `blit(BITMAP *,
BITMAP *, int, int, int, int, int, int)' lacks a cast
test.cc (28) Warning: passing `int' to argument 1 of
`destroy_bitmap(BITMAP *)' lacks a cast
There where some errors.

I do not understand that because the variables back and black should be
just as different as back and player1 or what???

Finally I tried my luck on my Othello game, changing all the bitmap
variables to *a, *b, *c, *d etc. to be certain that the variables had no
similarities in their wording. This worked wonders, and I even got the
game to show the BMP's with the right color scheme, so it was a great
success, but as a final test I changed the test program above in the
same way, using *a, *b as variables for the bitmaps, but then it showed
the test with a wrong color scheme????.

All these different results keep me perplexed as to what criteria's
Allegro is working with, when it comes to the dat file?

I would be interested in hearing any comments on this phenomena.

Sorry for this long posting.
Einar. 

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