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OpenTasks

Revision as of 12:44, 24 February 2010 by Bluddy (talk | contribs) (Updated loadable module task)

This page contains a list of open tasks. Completing any of them would benefit the ScummVM project a lot. At least in theory, all of them should be doable even by somebody relatively new to the project, in particular, as part of the Google Summer of Code. Besides the tasks listed here, there is of course also the TODO page listing more things that need to be done (but with far less details).

Introduction

Some basic rules

Below follow some basic rules that anybody interested in one of these tasks should adhere to. Sometimes exceptions may be possible -- as always, common sense applies, and if in doubt, ask.

The projects below are sketches and ideas. Plus, things evolve over time, so the descriptions might be slightly outdated by the time you read them (although we strive to keep them up-to-date). Hence, you should talk with somebody from the team, probably the person(s) listed as Tech Contact, before starting work on any of them.

All code, unless stated differently, must be written in clean and portable C++, in particular, GCC must be able to compile it (portability exceptions can be made for platform specific code, of course). We also have some Code Formatting Conventions. Using the standard C++ lib for code used inside ScummVM is at this time not possible. Using it inside non-essential tool should be fine, though.

All of the code submitted must be contributed under the terms of the GPL v2+.

We only accept clean and maintainable code. This is a somewhat vague requirement, but as a rule of thumb, if the code does what it is supposed to do, but is not extensible, a quick hack, or we need to rewrite it from scratch to properly integrate it, we will not accept it. In particular, we would rather have a maintainable, clean and incomplete piece of code that we could extend than a complete but unmaintainable piece of code.

Some good advice

The PostgrSQL folks have some real good Advice to Students on Submitting SoC Applications. We recommend all students interested in applying with us (or any other SoC project, for that matter) to read this.

Student application template

The following was adapted from the FreeBSD Proposal Guidelines.

  • Name
  • Email
  • Project Title
  • Possible Mentor (optional)
  • Benefits to the ScummVM Community - a good project will not just be fun to work on, but also generally useful to others.
  • Deliverables - It is very important to list quantifiable results here e.g.
    • "Improve X modules in ways Y and Z."
    • "Write 3 new man pages for the new interfaces."
    • "Improve test coverage by writing X more unit/regression tests."
    • "Improve performance in FOO by X%."
  • Project Schedule - How long will the project take? When can you begin work?
  • Availability - How many hours per week can you spend working on this? What other obligations do you have this summer?
  • Bio - Who are you? What makes you the best person to work on this project?

Your task

Anything you can dream of

Technical Contact: Our IRC channel, our mailing list, or contact Eugene Sandulenko, Max Horn

The Task:

Come up with your personal clever way to improve ScummVM and its various side projects. Be creative. Incorporate the ideas listed below and in our TODO, but don't let yourself be limited by them. Come up with something totally new, or enhance existing features. It's up to you.

But of course like with all the other tasks, we recommend that you first talk to us (see above).

Generic infrastructure tasks

Improve the ScummVM build system

Technical Contact: Max Horn, Eugene Sandulenko

Background:

ScummVM uses a custom hand-made Makefile based build system by default. In addition, we maintain a set of project files for various versions of MSVC, and some other development environments. Some of our ports tie into the default Makefile build system, but others need yet other project files (e.g. the PalmOS port).

This leads to the following problem. Whenever we add, move or delete files from our repository, the default build system is updated, but the other project files in general are not -- they have to be maintained separately. This is a manual task, and if forgotten, causes these project files to become out of date and hence more or less unusable. Therefore, we would like to be able to generate these project files from the master build system. For MSVC, this should be possible using a simple perl script, for example.

Another issue is the following: There are several people who develop 3rd party engines, which use the core code from ScummVM, but is not hosted within the ScummVM repository. Since ScummVM allows building engines as loadable modules, that is fine. However, in order to build these engines, one currently has to copy them into a checkout of the ScummVM trunk, and then hook them into the build system (by modifying the engines/engines.mk file). It would be so much easier if one could build an engine as a loadable module *outside* of the ScummVM source tree, and without any need to modify files in the ScummVm source tree. This is definitely doable, but needs somebody to implement it.

Then there are the ScummVM tools, which are hosted in a separate module of our repository. They currently use a very crude Makefile. It would be much better if they used a more powerful system (e.g. the one we currently use for ScummVM itself), as well as a configure file to detect required dependencies. Moreover, it would be good if the tools could share code with ScummVM, e.g. by hooking into the ScummVM build system somehow. (Please ask us for details on this very vague statement if you are interested in pursuing this ;-). In addition, it would be nice to be able to generate project files for the tools, too.

All of the above needs to be implemented in a portable fashion.


The Task:

  • Generate project files for various IDEs (MSVC, XCode, eclipse, ...) from the default build system.
  • Modify ScummVM build system to add ability to build engines ourside of the main source tree.
  • Enhance the build system of the ScummVM tools (they are in a separate Subversion module, and not to be confused with the tools included in the ScummVM source tree itself).

An alternative approach to hand-rolling everything described above would be to switch our buildsystem to CMake.

In any case, the resulting system must still work on Linux, Mac OS X and Windows, and all other platforms that relay on the default build system (e.g. WinCE, Nintendo DS, ...).

Required Skills:

  • Good C++ skills.
  • Excellent Makefile skills
  • Possibly experience with cmake or another meta-build system

Implemented support for loadable modules on small devices

Technical Contact: Max Horn | Yotam Barnoy

Background:

ScummVM by now contains about two dozen engines for different adventure games. Each of these takes up lots of storage space in the ScummVM binary, and hence also RAM, even if not used. Since both are scarce resources on some of our smaller targets (e.g. the Nintendo DS, which only has 4 MB RAM), this leads to problems. Some of the ports work around this by shipping multiple ScummVM binaries, each with a different subset of engines. This is not ideal, as it means more work for the developers and is confusing to users.

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.

The Task:

Implement support for loadable modules for at least two "small" targets where this is currently not possible. For the Dreamcast, Marcus Comstedt solved this by implementing a module loader on his own. Yotam Barnoy built on Marcus' work and made a similar loader for the PSP. You should probably use this version as a starting point.

The module loader consists of a linker script which is used to generate custom loadable modules "manually". Furthermore, we use a custom loader for ELF binaries which takes care of the run-time linking.

The original Dreamcast code is for Sh processors, and the PSP code runs on a MIPS processor. You would have to adapt these to generate and load ELF binaries for ARM processors (for Nintendo DS, WinCE, Symbian, GP2x), PowerPC (Nintendo Wii & Gamecube), or the PS2's version of the MIPS.

Ideally, your code should be generic enough to be usable for all platforms. With two examples of the loader already in existence, this should quite doable.

Another factor to consider is that should you wish to build the loader for very memory-starved platforms such as the Nintendo DS, you will have to deal with an issue within the ScummVm architecture. Currently, the loadable modules are all initially loaded into memory. When a game is chosen by the user, the irrelevant modules are erased from memory. In order for the modules to fit into the limited Nintendo DS RAM, this method will have to change -- only one module should be loaded into memory at a time.

Required Skills:

  • Good C++ skills.
  • Some knowledge of the ELF binary format (great documentation is available on the net, start e.g. at Wikipedia).
  • Any of the listed "small" devices (Nintendo DS, Wii, Gamecube, PS2, GP2x, any WinCE or Symbian device supporting ScummVM, ...) -- ideally multiple. Or figure out how to setup compilers for them.
  • Basic knowledge regarding the target architecture, be it ARM, PowerPC, or MIPS.

Small Devices Backend

Technical Contact: John Willis, Joost Peters

Background:

ScummVM has been ported to many platforms, often by simply re-using the SDL backend (which is based on SDL, which by itself has been ported to many platforms, making it fairly easy to port ScummVM to any of these platforms).

But for some platforms, dedicated backends are required, either because SDL doesn't support them, or because we can't achieve all our needs by using the SDL port (e.g. because we need more speed, more control, etc.). These backends are typically made for what we call "small systems" -- systems like PDAs, SmartPhones, Linux Tablets (PalmOS, SymbianOS, Windows CE, Maemo), or game consoles (Dreamcast, GP2X, Nintendo DS, PlayStation 2, PlayStation Portable).

These systems share many features. In particular they often have no (full) keyboard and quite limited resources: Little RAM, little permanent storage space, not that much CPU power, or a limited screen resolution.

This makes it often necessary to (re)implement certain functionality, like virtual keyboards (see above task), or graphic downscalers and the like.

The Task:

Since the same needs occur again and again, it would be nice to implement such functionality only once in a sufficiently portable and flexible way, making it possible for backends to pick and use whatever they need.

Details, scope and further suggestions as to how to achieve this can be found on the Small Devices Backend page.

Besides this, optimizing code for speed and memory usage benefits all our targets. In particular these "small devices". Hence doing this is a worthy goal on its own.

Required Skills:

  • Reasonable C++ skills.
  • Refactoring skills.
  • Knowledge of one or more ScummVM platform backends is desirable.

Add a testing framework for ScummVM's subsystems

Technical Contact: Johannes Schickel, Max Horn

Background:

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 file 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.

The Task:

As visible from the description above, we need a 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:

  1. 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.
  2. A "test" engine: Unit tests probably would likely only be runnable on "desktop" ports like Windows and Linux, and not on ports like PSP or NDS, due to run environment restrictions. To allow extended coverage on *all* ports, implementing a "test" engine would be helpful. In addition to running on all ports, the "test" engine also provides an environment to test things in an integrate, non-isolated way, unlike unit tests.It should test as many features as possible: game detection, file loading/saving, navigating the file system, testing graphics and audio output, etc. -- and it must be possible to verify everything. I.e. compare results to reference data, output progress data on the screen, create dump logs, and so on. Lots can be done here.

The test suite extension would be easiest to use on Linux etc. and there is already some existing code to build on. An 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 test 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.

Required Skills:

  • Reasonable C++ skills.
  • Experience with unit tests.
  • Knowledge about various ScummVM subsystems would be useful, but not required.
  • Knowledge about how to create a new engine for ScummVM would also be useful. See also our Engines HOWTO.

Also required:

  • Access to a non-desktop testing device (PSP, NDS, PS2, WinCE or Symbian mobile, etc.) and the ability to compile and run ScummVM on it (the ScummVM team would help with compiling and running).

Add a testing framework for ScummVM's engines

Technical Contact: Eugene Sandulenko

Background:

Number of ScummVM supported games grows with each release. Since 0.8.0 we are performing extensive prerelease testing. Basically it is game replaying for finding regressions. This becomes somewhat tiresome process and takes much time.

In fact there should be no changes in the gameplay in most cases, so event recording and proper replaying should be enough. There is some code for that based on Action recorder patch, but the recordings are not played consistently. The main problem is that there is no guarantee of the events to be in sync with other engine parts, so the playback may deviate, depending on the machine speed.

The Task:

Implement proper event recorder and player. It should be multiplatform and not depend on the CPU power. I.e. it should guarantee proper event sequence and time. It should store mouse, keyboard events, as well as generated random numbers and any other functions dealing with extern world such as time. Basically it should be implemented as some globally blocking cycle which will be driven by recorded events.

The format should contain also ways to give name to the recording, keep a screenshot, and optional savegame, so arbitrary portions of the game could be recorded.

Additionally there should be implemented possibility to create screenshots at specified intervals, so the output could be compared.

The GUI should preferably include an overlay image which will indicate that the game is being recorded or played back. But it will require some work in backends.

Optionally there could be implemented step-by-step mode with ability to pause the playback at any place. And as a big bonus ability to annotate the recordings with on-screen messages could be also implemented.

Required Skills:

  • Good C++ skills.
  • Knowledge about a backend is preferable.
  • Knowledge about an engine is preferable.

Also required:

  • Access to a non-desktop testing device (PSP, NDS, PS2, WinCE or Symbian mobile, etc.) and the ability to compile and run ScummVM on it (the ScummVM team would help with compiling and running).

Improve the default ScummVM backend by adding OpenGL support and providing a common base class.

Technical Contact: John Willis

Background:

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.

We would also like to refactor the common aspects of the SDL backend into a common base class to better support backends that derive from it. Architecturally this could be very elegant and allow platforms to derive from the common SDL base (inc. the OpenGL and default existing one) and future platforms could also derive from the OpenGL base etc.

There are a number of required features that the extended backend must have.

The Task:

  • Allow for arbitrary rate scaling using OpenGL/OpenGL ES.
  • Be well written and maintainable!
    • This could become part of the default choice for ScummVM’s user base so really does have to be well architected.
  • Offer a fallback to the existing rendering code if OpenGL support is not available OR not desired by the user. This should be configurable at run time and maybe via a config setting?
  • Support removing the new OpenGL code at compile time by the use of structured defines so that NO OpenGL code need be built if not required.
    • We have a number of ports that derive from the SDL backend and really could not cope with the code bloat.

Also required:

  • This task will require testing under both OpenGL and OpenGL ES API’s.

Required Skills:

  • Reasonable C++ skills.
  • Refactoring skills.
  • Knowledge of the OpenGL and SDL API’s.
  • Knowledge of the default SDL ScummVM platform backend is desirable.

Audio related tasks

Audio output selection

Technical Contact: Johannes Schickel, Max Horn

Background:

Right now, our user interface and our internal API for selecting and controlling audio output are very limited. They do not properly differentiate between the output type, the output driver and the output device. To explain the difference:

  • An output type could be MIDI, AdLib, (PC) speaker, Amiga, etc.; MIDI could be further split into GM (General MIDI), MT-32, Roland, etc.
  • An output driver is a concrete implementation of an output type. For example, we have two AdLib/OPL drivers right now; and many MIDI drivers.
  • Finally, a single driver could control multiple devices; e.g. you might have a General MIDI synthesizer *and* an MT-32 attached to your computer; or you might want to use fluidsynth with two different sound fonts, each shown as a separate "device".

These different concepts are currently not properly distinguished. Furthermore, the approach we use to deal with MIDI variants like GM, MT-32 and Roland, is rather weird and irregular. This all results in a rather confusing way to select the output device -- for engine developers, for audio output developers, and for the user in the GUI. Clearly, this is a bad thing for all involved parties and hence the goal of this task is to fix this mess.


Let's start by reviewing the current state of affairs. Engines specify during a startup a set of audio output flags. These flags try to describe the output types supported by the engine resp. the current game. We then use some (pretty simple and stupid) "detection" method based on these to determine the output driver to use. (There is no support for output devices in ScummVM right now, and adding support for this is not part of this task, but of course we won't complain if it happens either.) Unfortunately, this detection does not include all the above mentioned output types, for example it does not allow to specify "Amiga", which recently turned out to be a major problem for the WIP SCI engine, since its Amiga games support both MIDI (in this case, MT-32 MIDI) and Amiga sound output. Now there is no (clean) way of checking whether the user wanted to use Amiga sound or MT-32 MIDI. Next it does directly map to some concrete audio driver (like ALSA or Windows MIDI for MIDI). This results in an unclean way of checking in the engine what exactly the selected output type is (this might be required to load special music data files for the different output types). To further complicate things, the current "AdLib" music driver is also used to emulate MIDI sound (useful on low end system which don't properly support MIDI output on their own), causing several engines which only use MIDI for audio output, and which don't contain and AdLib data, to still specify the MDT_ADLIB audio flag.

For the user we currently always show all concrete output implementations (except digital sound!) in the GUI, without distinguishing between output types and output drivers. We also always show everything, without considering what a given game actually supports. So currently the user can select "AdLib" sound for a game which does not contain any AdLib sound data. This is rather annoying.


To overcome these issues it would be best to change our audio output configuration API to use different layers of configuration:

  • The first layer would be the output type. As described above, this could include General MIDI, MT-32 MIDI, AdLib (or generic OPL* output), (PC) Speaker (this might also include PCjr and CMS, to be determined later on), Amiga, FM-TOWNS, Digital Output etc. Note that this is no final list, rather making this list concrete is part of the task! For example, one might want to have a single MIDI output type, and introduce a notion of subtype to distinguish between GM, MT-32 and Roland MIDI.
  • The next layer would probably be a concrete output implementation, i.e. output drivers. Examples include Windows MIDI or ALSA for MIDI. Note that a single driver could potentially support multiple types: A user may usually use the Windows MIDI driver for GM output, via software synthesis, but may also own a real MT-32. This user may then wish to use the MT-32 via the Windows MIDI driver. Hence, depending on the output device resp. the user choice, the Windows MIDI driver would accept any MIDI variant. On the other hand, the MT-32 software emulator might only support MT-32 data.
  • One could also insert an extra conversion layer which tries to (optionally) translate between the various MIDI variants: So if a game requires MT-32 output but the user only has a GM device available, the MT-32 data could be translated on the fly (as good as possible) to GM before being sent to the actual output driver. Such conversions currently happen in engines. Sharing this code might be beneficial; on the other hand, it might turn out that each engine knows best how to perform this translation, in which case we should leave it up to the engines to perform such a conversion (or not). Once again, deciding this is part of the task.

So if you plan to take this task, you will still have a lot of research to do, to find the best separation :-). Of course the technical contacts, as well as the rest of the ScummVM team, would collaborate with you on this.

Roughly the same layers should also be visible in the GUI configuration to allow for a much more user friendly output configuration. The user might additionally configure a concrete output driver like ALSA to use a specific implementation specific setting (like in the output port for ALSA); think of this as a baby version of output devices (for true output devices, one would have to support multiple such configurations for each driver, configurable and selectable via the command line, GUI and the internal API). See the MIDI_device_configuration task for more thoughts about this. (Note that it would probably best to tackle both tasks in a single Google Summer of Code project!).

Of course this is not set in stone yet; if you have some other great idea how to tackle this, we are happy for your feedback :-).

The Task:

  • Design a proper layer based audio output system.
  • Implement the API.
  • Adopt all engines to use it.
  • Adopt the GUI to reflect the changes.
  • (Optionally) also extend all engines to supply a list of supported audio devices for a specific game target. (This would be done via the help of engine authors).
  • All configuration must be serializable for our configuration file. (And it would be nice to have some auto update feature for old configuration files!)

MIDI device configuration

Technical Contact: Max Horn

Background:

Many of the adventures supported by ScummVM make use of MIDI music. Which is why we already include several device drivers for various MIDI APIs and emulators (e.g. ALSA, Windows MIDI, Mac OS X CoreAudio/CoreMIDI, fluidsynth...).

Right now, the MIDI drivers (and more generally, audio drivers, see the previous task) are treated by ScummVM in a rather single minded fashion: Either a driver is linked in and hence "available", or not. It's not possible to configure anything about them (like ports to be used etc.), nor does it ever take into account that a single driver might correspond to multiple devices (after all, you can plug several sequencers into your MIDI port; or you could have configured several different sound font settings in your MIDI emulator). These two issues are very tightly related.

TODO improve and extend description, and integrate it better with the Audio output selection task

Some more details can be found on the Music drivers redesign Wiki page.

The Task:

  • Add an API for querying the OSystem backend for a list of available MIDI devices (not drivers)
  • Information about the selected device must be serializable, so that it can be stored in the config file
  • Selection of devices via command line should be possible
  • It must deal with devices being added/removed (at least between runs of ScummVM, ideally also while ScummVM is running)
  • Devices should be configurable via the GUI; this needs to be done in a flexible (different devices/drivers offer different settings) and portable fashion.

XMIDI parser

Technical Contact: Max Horn

Background:

Several of our games make use of the XMIDI format. We already have a parser for it (see sound/midiparser_xmidi.cpp), which was based on code from the Exult project, but it is incomplete.

The Task:

Specifically, we require support for XMIDI_CONTROLLER_FOR_LOOP and XMIDI_CONTROLLER_NEXT_BREAK. There are many more XMIDI controllers, however, and ideally support for all of them would be great. Some references:

  • The XMIDI code from the Exult project (see Exult's audio/midi_drivers/XMidiSequence.cpp) could be used as a reference again.
  • In addition, Pentagram has XMidi code based on the Exult code, but may be cleaner (see here.)
  • Another good reference for this task is the AIL library which has been recently open-sourced by its author. This is infact where XMIDI comes from, and it even contains specs. To find them, unzip AIL2.ZIP; in there you find A214_D2.ZIP, which when unzipped contains a dir DOC, which in turn contains ASCIIDOC.ZIP, which then contains XMIDI.TXT and some other files which might be of use (e.g. NOTES.TXT).

Accolade MIDI parser

Technical Contact: Travis Howell

Background:

The Elvira 1 (DOS), Elvira 2 (DOS), Waxworks (DOS) games of the AGOS engine use the Accolade MIDI format for music. The current parser (see engines/agos/midiparser_s1d.cpp), is based off looking at the music in the DOS Floppy Demo of Simon the Sorcerer 1 (Which was based Waxworks engine) and guess work. The current code frequently crashes when changing locations in Waxworks, due to invalid MIDI data been passed along.

The Task:

Updated the current parser, to completely support the Accolade MIDI format used by these games. There are already comments in the current code, about where each additional MIDI event is triggered in the music of these games.

Support for Acorn Audio Format: Desktop Tracker

Technical Contact: Eugene Sandulenko, Sven Hesse, Kostas Nakos

Background:

Since we're adding (and have added so far) support for different platform game versions, we need support for the sound files too. Currently we need support for following format:

  • Desktop Tracker format used by music in the Acorn disk version of Simon the Sorcerer 1. Information about the specifications of the Desktop Tracker format and sample mods are available.

The Task:

  • Extend our general MOD player to support the mentioned format

Required Skills:

  • Good C++ skills.
  • Understanding of how audio is generated.
  • ARM assembler knowledge is a big plus.
  • Acorn knowledge is a plus.

Improve sound support in SCUMM games

Technical Contact: Eugene Sandulenko, Travis Howell

TODO: Is this task really suitable for this wiki page? It seems to be very specific and has a high entry barrier (esp. for the Apple II part). At the very least, a more detailed description is necessary.

  • Add support for beeper sound used by the Apple II version of Maniac Mansion to the SCUMM engine. Unfortunately there is no demo versions are available, so you need to own the game. Known information about the resource format can be found here.
  • Add support for sound format used by Macintosh version of Loom to SCUMM engine. Known information about the structure of the sound resources used is available. If you don't own the game, the LucasArts Mac CD Game pack is usually available via eBay.

Tools

Tools: Game script (bytecode) decompiler

Technical Contact: Max Horn, Johannes Schickel

Background:

Most adventure engines ScummVM supports are driven by bytecode scripts, which control the game behavior. For various reasons (in particular, debugging), it's very useful to be able to take such a script and decompile it into something resembling regular code (with variables, loops, if statements etc.). We have a tool for doing this for the bytecode used by SCUMM games. This tool is called descumm. We also have similar (but less advanced) tools for various other engines, in our tools module in SVN.

Currently, descumm use a relatively crude heuristic to detect "if" statements, loops and so on. In particular, it only supports loops with the condition at the start (think "while(...) { ... }" ), not such with the condition at the end (as in "do { ... } while(...)" and also suffers from various other limitations (like not being able to correctly recognize "continue" and "break" statements.

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.

The Task:

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 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.

A good starting point for this might be the [Jode] Java bytecode decompiler which does a pretty good job at decompiling. Another useful site might be [1], and this thesis. The technical contact has several ideas on how to approach this project, too -- as usual, you are expected to talk to us and ask for help and ideas!

The tool should run on at least Windows, Mac OS X and Linux. Acceptable languages include C/C++, Python, Perl -- other languages might be OK, but please consult with us first -- after all, other developers also will have to use and maintain your code. For the same reason is is obviously mandatory that your code be well documented.

Actually, we probably would prefer if it was written in C++ and was written as kind of a library, with the command line tool just a frontend to the library. This "library" approach would make it possible to include the decompiler into ScummVM itself, making it possible to decompile scripts on the fly from ScummVM's built-in debugger console.


Note:

This task was being worked on as part of the Google Summer of Code 2007 and again 2009, but unfortunately in both cases the result sadly is incomplete and never reached a status we are satisfactory with. It is probably best to start from scratch, but you can find the code from 2007 here and the code from 2009 here.

Engine/game specific

Objectify CruisE engine

Technical Contact: Eugene Sandulenko

Background:

The cruisE engine also started out as an external project started by Yaz0r. Originally it was written in plain C. ScummVM is a C++ project, so we need to objectify this engine without changing/breaking its behavior. The engine is fairy complete, but also suffers from portability problems, that is it works correctly only under little-endian, alignment-agnostic CPUs.

The engine itself is well-structured, hence many functions / variables which might be good candidates for being grouped together into a C++ class are already grouped by files.

No deep knowledge of the engine internals is required too.

We have previously "objectified" several other engines, namely SAGA, Gob and AGI, so one can learn a lot about various approaches how to do this by tracing through our SVN repository.

Improve AGI engine

Technical Contact: Eugene Sandulenko

Background:

Our AGI engine is in quite good shape. Still it misses some important aspects.

The Task:

  • NAGI has better Tandy music support, particularly noise channel emulation is better there. NAGI license lets use its code directly in ScummVM. For the most authentic model MAME could be referenced, though its license is not GPL-compatible
  • Add support for AGI 2.01 games, such as Donald Duck Playground
  • Add support for AGI0 and AGI1 (bootable floppies) games
  • Document all differences between AGI versions on Wiki and probably in code
  • Cover more tasks from AGI/TODO page

Required Skills:

  • Good C++ skills.
  • Engine internals could be studied within a week or less.
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