From: "John M. Aldrich" <fighteer AT cs DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: images
Date: Tue, 14 Apr 1998 01:14:29 -0400
Organization: Two pounds of chaos and a pinch of salt.
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laine wrote:
> 
> >     Hi, I'm really new to allegro... can someone please
> >  tell me how to simply load a bmp, jpg, or pcx, and use arrow keys
> > to move it across the screen?
> >
> Sure,
> 
> Here's a little something that might help you. A little program.

Which doesn't work.  Thanks for the effort, but you need to test code
like this before posting it if at all possible.

First off, you forgot to #include <allegro.h>, which is rather a vital
first step to any Allegro program.

> 
> void main(void)

Please don't post examples using this syntax.  ANSI C requires that
main() return an integer.  See question 11.12 of the comp.lang.c FAQ
(http://www.eskimo.com/~scs/C-faq/top.html) for more information.

>     the_image=load_pcx("filename.pcx",palette); // This is the function you
>                         // have to use for loading .pcx-files, I havent used
>                         // the others, so I don't know about them, but 
>                         // surely you can find them in the documentation

It would help to test for the failure of load_pcx() here; otherwise
you'll be risking major pointer catastrophes.

>     create_bitmap(10,10); // Before you can use the bitmap, you have to
> create
>                         // it by telling it's size.

This call is useless, since load_pcx() should have already returned a
correctly sized BITMAP *.  Besides, you don't assign its value to
anything.

>     set_pallete(palette);   // Sets the loaded palette

Umm, where do you define this 'palette' variable?  You forgot a "PALETTE
palette;" at the top of main().

> 
>     while(!key[KEY_ESC]){               // While no-one has hit ESC
>         blit(the_image,screen,0,0,x,y,10,10);
>                         // Blits the image on the screen from (0,0) to
>                         // (x,y) - the size of the image is 10,10

It's better to use the_image->h and the_image->w instead of preset
values; load_pcx() calculates these automatically so you might as well
use them.

>         // Keyboard
>         if(key[KEY_LEFT]) x--; // if you press left..
>         if(key[KEY_RIGHT]) x++;
>         if(key[KEY_UP]) y--;
>         if(key[KEY_DOWN]) y++;
>                 // This is easy.. just: key[KEY_name_of_the_key]
>                 // ie. key[KEY_ALT] or key[KEY_A]

This rapid blitting without waiting for vsync() could cause a very
messed up image.

> 
>    }
> 
>    allegro_exit(); // Makes everything as it was before
> }

Add a return 0; before leaving main().

> 
> There might be some faults in this program and it's not very good.
> It doesn't use double buffering (wich you should use..) or any other
> nice stuff. But it does what it's supposed to do (I hope so, I haven't
> tested it, I just wrote it here for you). Hope you find something
> in it. Good luck.

With code as dangerous to your computer's health as graphics is, you
should always test examples before posting.  Please take this as
constructive criticism; I don't mean to offend.

l8r

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