Difference between revisions of "HOWTO-Backends"

I will assume that you are at least roughly familiar with ScummVM, and have a fresh checkout of our Subversion repository. Note that it's strongly adviced to base your work on the current development version of ScummVM, and not on a release version. This will ease integration of your work.

Essentially, you will have to implement a subclass of the OSystem class. Our Doxygen documentation is your friend and should hopefully explain enough about this, see here: http://scummvm.org/docs/doxygen/html/classOSystem.php.  

In the following I assume your port is named "foobar" (very clever, isn't it? :-).

# Create a new backends/ subdirectory matching your engines name, i.e. <tt>backends/foobar/</tt>

# Populate the new directory as you need to. If you want to use our regular build system, you will want to provide <tt>backends/foobar/module.mk</tt> file. Take a look at <tt>backends/sdl/module.mk</tt> for an example.

# Subclass OSystem. You could copy the content of <tt>backends/null/null.cpp</tt> to <tt>backends/foobar/foobar.cpp</tt> to get a skeleton. As you progress, it might be helpful to look at other backends to learn how they do things.

# Instantiate OSystem class and assign it to <tt>g_system</tt>, do that before calling <tt>scumm_main</tt>

# Deinit properly after calling <tt>scumm_main</tt>, particularly call <tt>g_system->quit()</tt>

  int main(int argc, char *argv[]) {

      g_system = new OSystem_Foobar();

      assert(g_system);

      // Invoke the actual ScummVM main entry point:

      int res = scummvm_main(argc, argv);

      g_system->quit();

      return res;

  }

 

TODO: This section is meant to give some specific hints on creating a useful OSystem subclass. For now I can't really think of anything useful besides the obvious, and besides what we already say in other places... Take a look at http://scummvm.org/docs/doxygen/html/classOSystem.php which contains lots of useful information. Also take a look at null.cpp to see what you have to implement, and peek at the SDL backend (which is our main backend and thus kind of a reference for all the others). And finally, take a look at <tt>common/system.h</tt> to see which methods are pure abstract, and thus *must* be implemented by you. Oh and of course: You can always talk to us on IRC or via email :-).

There is [[Small Devices Backend]] in the works which is planned to be common for all devices with limited resources. If you are working on a backend for such a system, you may want to take a look on that page!