DOS - Modern Development Tools

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Sample makefiles
- 286 / Real mode target
- 386 / Protected mode target

OpenWatcom

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Downloads
Sample makefile

DJGPP / GCC

Allegro 4

Homepage
Documentation
- Official documentation at liballeg.org - downloadable versions only
- Alternative documentation at allegro.cc
Downloads
- allegro-4.2.3.1.djgpp.bin.tar.bz2
- The above includes Allegro 4.2.3.1 built and patched for DJGPP, with all example code, normal, debug and profile library versions and html docs. This unpacks to /opt/toolchains/x86/allegro-djgpp.
- CWSDPMI.EXE (at the official homepage or the information on Wikipedia)
- You need cwsdpmi.exe, above, (or an equivalent DPMI server) in order for DJGPP binaries to run on DOS.

Allegro was basically SDL for DOS, before SDL was even a thing (SDL is great, by the way and I use it a lot!). It's a full featured graphics and audio game library for DOS and a number of other platforms - it's still around and being developed, but dropped support for DOS many years ago. It's probably the most full featured, freely available graphics/audio SDK for DOS. There are versions of it floating around the net pre-packaged with ancient versions of the DOS DJGPP toolchain, but by far the best way of using it these days is via a cross-compiler toolchain such as DJGPP on Linux/Mac/Windows.

How to build on modern compilers? Well, first of all don't use Open Watcom; I started off via this route and everything appears to work just fine, but later on I got to the point of needing to set up the Allegro timer/interrupt functions and I started getting unexplained program termination at the point (or just after) the Allegro timers were initialised. I eventually relented and rebuilt Allegro using djgpp and switch to that, with the exact same lines of code the application stopped exiting at the point the Allegro timer was initialised.

I can only guess that Watcom/Open Watcom was not fully tested at the point the last release of Allegro for DOS was released in 2009. My experience tells me that it is not a fully working combination. Stick with DJGPP.

The outline process is simple:

Download 4.2.3.1 source
Unpack
Configure for DJGPP cross-compilation (run 'fix.sh djgpp')

But as always, the devil is in the details. If you want to use a modern version of GCC/DJGPP (and you *really* do), you have to make a few changes. First you have to edit xmake.sh to pick up your DJGPP install. In my case it was setting the two variables XC_PATH and XPREFIX to the following:

xmake.sh

XC_PATH=/opt/toolchains/x86/djgpp/bin
XPREFIX=i586-pc-msdosdjgpp-

Next edit makefile.dj to set a compatibility option for the modern GCC compiler (the '-fgnu89-inline' directive). If you don't, things look like they work until you try to link against Allegro and your code will fail to compile due to duplicate symbol errors (there are a lot of inline defines in the Allegro headers, which are deprecated on C99 syntax):

makefile.dj

TARGET_OPTS = -fgnu89-inline -O2 -funroll-loops -ffast-math

Finally, there is a bug in one of the graphics drivers that comes with the 4.2.3.1 release, and it results in two missing symbols when compiled with GCC. You need to edit src/misc/vbeaf.c and add them. Just before the following lines:

src/misc/vbeaf.c

* the video driver structure */
GFX_DRIVER gfx_vbeaf =
{

Change it to show the following:

src/misc/vbeaf.c

int int_ds;
int saved_ds;

/* the video driver structure */
GFX_DRIVER gfx_vbeaf =
{

Now you are ready to compile Allegro from source:

./xmake.sh lib
cp -a include /to/where/you/want/the/allegro/headers
cp lib/djgpp/lib*.a /to/where/you/want/the/allegro/libs

You can optionally build the demo application as well:

./xmake.sh demo

However, the examples and many other bits of the DOS runtime (such as the keyboard/sound setup utilities) don't get built via the cross compile process, so they need to be built manually:

cd allegro-4.2.3.1
cd examples
for src in *.c; do
  i586-pc-msdosdjgpp-gcc -I/to/where/you/want/the/allegro/headers -g -O2 -o ${src%.c} $src /to/where/you/want/the/allegro/libs/liballeg.a -lm
done
cd ..
cd setup
i586-pc-msdosdjgpp-gcc -I/to/where/you/want/the/allegro/headers -O2 -o setup.exe setup.c /to/where/you/want/the/allegro/libs/liballeg.a -lm
i586-pc-msdosdjgpp-gcc -I/to/where/you/want/the/allegro/headers -O2 -o keyconf.exe keyconf.c /to/where/you/want/the/allegro/libs/liballeg.a -lm

.. you'll want to copy the following to the application/game you are writing, since these are used to allow users to configure their sound/video options:

setup/setup.exe
setup/setup.dat
setup/keyboard.dat
language.dat & allegro.cfg (both found in the main allegro-4.2.3.1 folder)

There are some more hoops to jump through in order to build documentation, but if you want to skip all of this and just use a pre-compiled library, with the headers, examples, setup/keyboard utilities, the main demo and documentation all built and configured, just grab the archive I uploaded, above: allegro-4.2.3.1.djgpp.bin.tar.bz2

Most of the DOS binaries (.exe files) in my archive have been compressed with upx, if you build from source you will want to install and use upx, as otherwise you'll find that even the tiniest Allegro tool will be 700-800KBytes in size (you pretty much end up with an entire copy of the Allegro library embedded in each one due to the limitations of the linker/runtime on DOS).