Re: [AL] Allegro and OpenGL

[<oe...@ca...>]

> [snip]
> > However this means that I can only use OpenGL to draw to the screen
> > (Allegro and GDI functions only access the front buffer, and the MSDN
> > documentation seems to say that you can't access the back buffer)
> 
> Yeah, this is exactly as far as I got when I was looking into how to do
> this. I couldn't see any way to get them both double buffering in a
> sensible way, and without that the support is kind of cool but useless for
> writing any actual games. 

Well, you could do it if you were prepared to have the 2D and 3D 
parts completly seperate, ie use Allegro for all the 
save/load/options menus, then switch over to openGL for the game. 
Unfortunatley I can't do that with mine.

> Which sucks very much: there can't be any
> technical reasons why they wouldn't give you a DC to the backbuffer,

Once when I was trying to get it working, I wasn't clearing the 
colour buffer between frames, and then WinAmp appeared behind 
my landscape, but it wasn't flickering like when I tried to use 
allegro/GDI to blit things to the screen. The interesting thing was 
that I could see all the winamp windows (main screen, equlizer, 
playlist) and in windows only the main screen was showing. 
However it wasn't quit displayed correctly, it was stretched to twice 
its normal width, and the animated parts were just a yellow line 
with random colours moving down it.

> that. It looks to me like they just didn't think this through carefully
> enough to see how useful a backbuffer DC would be. Or perhaps they were
> worried that some obscure hardware might not be capable of it, but that's
> no reason to cripple the 99% of consumer cards that don't have any such

Prehaps they thought that a useful feature like that should be 
reserved for a superior, reliable, widely used API like Direct3D ;-)

I was looking at the possibility of useing OpenGL as an Allegro 
driver. Although OpenGL can directly access 32bit allegro bitmaps 
(BGRA_EXT format) the MS-OpenGL "blit" command glCopyPixels 
(?) is horribly slow. So the only way of "bllitting" something would 
be to load the bitmap into a texture, then render a quad. However I 
think loading the bitmap for the first time would be just as slow as 
glCopyPixels (I haven't tried it yet though). Also the "screen 
bitmap" couldn't be changed, to another video bitmap.


Owen Embury
   http://ban.joh.cam.ac.uk/~oe203
   oe...@ca...
>From <all...@ca...> Tue Sep 07 05:30:29 1999
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From: "Dominique Biesmans" <d_b...@ro...>
To: <al...@ca...>
References: <001201bef8be$c9fb0ae0$0700a8c0@avenger>
Subject: Re: [AL] lcc-win32
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----- Original Message -----
From: Henrik Stokseth <hst...@c2...>

> i'd love to make a port, but i assume there are people much more qualified
> for that task than me. the nice thing with lcc-win32 is that it is able to
>

It shouldn't be too hard to make Allegro work with lcc-win32. DJGPP users
should like lcc-win32, it's assembler uses AT&T syntax :-)

> i just discovered that cygwin takes $6000 per 'commercial developer'
> license, which i think is insane, so i'll not use their compiler, just in
> case i decided to make some commercial software someday.
>

Their 'commercial' license doesn't mean you have to pay if you want to use
cygwin for commercial products. It's more like a support program for
companies who'd like to use cygwin & get lots of support with it. (A
perfectly legitimate way to make money from open source software, BTW).
Anyway, Mingw32 programs don't link to the cygwin library, and thus are only
subject to GNU licenses.

Dominique