Difference between revisions of "Summer of Code/GSoC2010"

This pages lists students and projects for the [http://www.google-melange.com/archive/gsoc/2010 Google Summer of Code 2010]. See also Google's [http://www.google-melange.com/archive/gsoc/2010/orgs/scummvm ScummVM organization info] page.

ScummVM is a highly portable application. To achieve that, there are different interfaces to access platform specific functionality. Our APIs are usually well documented, thus giving porters and engine authors a clear vision of how different functions / methods are supposed to work. Apart from the lower level platform abstraction APIs we usually offer more high level APIs for engine authors.

For example we have a low-level filesystem abstraction API: FSNode. This can be used to browse directories, open files, create new files for writing etc. Since the API is pretty much low level, engine authors usually do not use it directly, but use some wrapper code to access it. To prevent code duplication and take work from engine authors we introduced the Archive and SearchMan classes. SearchMan can be easily used to access game data files without fiddling with FSNode.

However, experience has shown that the documentation of all these classes is not always as clear and complete as it should be, and sometimes might be misunderstood. In addition, the implementations for the various systems we run on may not adhere to the documented specification and/or regressions were introduced when doing changes to the code. Currently we have only a very minimalistic test suite in "tests/", testing only a tiny subset of our code: container classes, string handling and some stream code. Currently it is hard to do proper regression/implementation testing for other APIs, for example FSNode API.

As visible from the description above, we need an automated test system to help ensure our implementations are bug free. We need both a framework for the tests, as well as an extensive test suite. There are several different approaches to testing which all are of independent interest and complement each other:

# Unit tests: Add many more tests to our test suite in "tests/". This would also require some enhancements to our build system, since currently we do not link against all of our code for the test suite. Also new test mechanisms are needed to make it possible to e.g. test audio & graphics output (e.g. code that can load an existing reference image and compare it to the output of a graphics primitive). It might also be helpful to enhance the "null" backend so that all unit tests can be run against that, headless (good for automated tests on a server with actual graphics/audio output).

The test suite extension would be easiest to use on Linux etc. and there is already some existing code to build on. A test engine would work on all ports, including game consoles and phones, and is nice for testing in a more "holistic" and complete way. Of course best would be to have both, and also make it possible to run all unit tests from inside the test engine.

Overall the test engine has the highest priority, since it would give us the possibility to test ''all'' ports without additional work. Thus the primary task would be to implement and document at least a test engine, which tests (preferably) all of ScummVM's subsystems extensively.

Putting all engines into loadable modules reduces memory usage, as this way during game play only a single module needs to be in RAM. ScummVM itself is prepared for loadable module support. In fact several of our ports, notably the Windows, Linux and Mac OS X ports, already support loadable modules. This is easy for them as the operating system already provides loadable modules. But this is not the case on systems like the Dreamcast, Nintendo Gamecube & DS & Wii, the PlayStation Portable, Symbian and others.  

Once loadable modules work, there are potential tasks beyond this, which could be pursued if enough time is left. For example, on the NDS, even when only one engine is loaded, memory can still be too tight unless the core binary itself is reduced. Therefore, the NDS port disables MP3 support in certain engines, as well as certain other core features. But we would prefer to have a single binary which only loads modules as required. So, maybe one can turn the MP3 decoder (as well as other audio and video decoders and maybe further core components) into plugins, too, and only load them when required. Of course this opens up issues of its own, like now modules would have to be able to declare dependencies on each other.

Since its inception, ScummVM has offered a default cross platform backend that makes use of the extensive and prolific SDL API. We have no intention to change this but we would like to extend the default backend to take advantage of things like OpenGL, and its little brother OpenGL ES, that is becoming commonplace on the latest generations of devices.  

The whole thing is somewhat complicated by the fact that there are two main versions of this bytecode: V5 and older (register based bytecode), and V6 and newer (stack based). We handle the registed based code quite well, but not so the stack based one. And in fact most non-SCUMM engines use a stack based virtual machine.

Write a ''generic'' bytecode decompiler with the goal of ultimately being able to decompile bytecode of all games which use a stack based bytecode virtual machine. You can look at existing work from GSoC 2007, our descumm compiler (only SCUMM v6 and newer is stack based) and some other de*.cpp files in our [http://scummvm.svn.sourceforge.net/viewvc/scummvm/tools/trunk/ tools SVN module]. Your goal should be to support at least two different bytecode systems (i.e., from two different ScummVM engines). But everything should be designed and implemented with the ultimate goal of being able to support all such bytecode systems (e.g. by providing a suitable API or subclassing facilities that make it possible to hook in parsers for arbitrary bytecode variants). Engines which use a stack based virtual machine include SCUMM v6+, KYRA, SWORD1, SWORD2, ... For many of these, free game demos are available, too. We would help you by providing dumps of scripts etc.