Thread: ALLEGRO Question

Hello...after reading several posts on this board I went hunting and grabbed all the components of the DJGPP compiler as well as the Allegro add-on. I can get all the Allegro examples to run (this I take as proof that I have installed it correctly =) and if I follow an example exactly I get the correct result. But with the following example only gives me a white screen...no errors during compile and it ends cleanly

#include <stlib.h>
#include <stdlib.h>

#include "allegro.h"

int main()
{
BITMAP *scr_buff;
allegro_init();
install_keyboard;
set_gfx_mode(GFX_VGA, 320, 200, 0, 0);
set_pallete(desktop_pallete);
scr_buff = create_bitmap(320, 200);
clear(scr_buff);
vline(scr_buff, 100, 20, 150, 255);
// I have tried every primitive routine that uses the bitmap pointer
// not sure if I am doing something wrong here
destroy_bitmap(scr_buff);
readkey();
return 0;
}

Please if anyone has a suggestion let me know...it is getting very
frustrating.
BTW I am running win 98 and using a voodoo 3 2000 agp video card..maybe that has something to do with it.
TIA

Opps....didn't mean to cross-post but at first I was thinking this was a c question but then thought no it should be a graphics question **sorry**

I don't see anything wrong with the code, but I just switched to DJGPP a week ago so I'm still learning it as well. Have you tried recompiling the example programs without altering them? If the executables work obviously it's not the fault of hardware incompatibilities, so there is probably something wrong with your code or compiler. If you can't recompile the example sources, there's something wrong with the compiler; otherwise you just made an error in the code. That's really all I can say...


Edit:

Actually, I think I just figured it out. Replace scr_buff with screen in your primitives calls. I think screen is a global variable which points to the video memory; use that if you want to see your output.

You're right replacing the scr_buff with screen did work...and yes I can make all the examples compile and run. Now it would seem I am confused with allegro. Why create a pointer to the video memory you carve out and use it as a passing arguement if screen will work as a global...do you even need to create a bitmap if you use 13h?

hmmmmm.....

You don't need to create an additional bitmap for using graphics primitives; I think the global screen bitmap should take care of it entirely on its own.

However, if you want to load sprites, backgrounds, tilesets, and textures in from disk and keep them in memory (an absolute necessity for most games) you'll need your own additional bitmap objects to store them in before blit-ing to the screen.

Sorry; for clarification, that was my post. For some reason I wasn't logged in.

um, your going to kick yourself for this mistake but you forgot to blit the scr_buff to the screen.

No

your code should run like this

while(ingame)
{
update_logic(); //update positions of players and make sure player doesn't want to exit
draw_to_buffer(); //draw all the players and enemies to buffer

vsync();
blit_from_buffer(); //draw buffer onto screen
}

im friggen telling you, the reason it isn showig up on the screen is because you are not drawing it directly to the screen.if you dont do that then you have to use the allegro blit function to "merge" the scr_buff with the screen bitmap.

example...

blit(scr_buff, screen, 0,0,320, 200);

//i think thats right, might wanna double check.