Difference between revisions of "Advanced Detector"

If your engine supports a large number of games, or variants then detecting them can be tricky.

As some of the game variants will have files with the same name, but differing contents,  

for a "magic header" is not reliable either.<br>

So instead you will take a checksum or even better a hash of the file to detect the exact version, then you will need to write this code to open the files and run this check into your custom MetaEngine...

Well to avoid every engine author having to do this themselves (and the codebase

ending up with the maintenance headache of 20+ implementations of this which are almost, but not exactly the same!), the ScummVM Infrastructure Team have provided the '''Advanced Detector'''!<br>

This structure plus other parameters are passed to the AdvancedMetaEngine constructor, which can also contain overrides of the default parameters for detection e.g. _md5Bytes is the number of bytes used for the MD5 hash for

each file, etc.

The main section with predefined name 'scummvm' contains global options, which are mainly editable in Options dialog in GUI. Then there go sections for each separate game. Additionally some of ports define their own service sections.

Advanced detector tries to match files in probed directory against specified lists of file characteristics provided in an array of ''ADGameDescription'' structures. It takes into account MD5 sum of the file or its first several hundred bytes, its size and name. It creates list of candidates which then it tries to narrow down to a single ''ADGameDescription'' instance unless it is told to do otherwise. In case of disambiguates it returns list of games.

It is important to know, that currently there are in fact two modes of Advanced Detector. First one is used during the game detection when user tries to add a game (detection mode), and second one when the user launches already detected game (running mode). Both uses call same method findGames() which potentially could return list of games. In detection mode the user is then represented with list of games to choose from, but in the running mode in case findGames() method returns more than one game, only first one in the list will be used. This may lead to situation when the game gets detected but doesn't run, thus it is important to test detection and avoid any disambiguates. This is also the main reason for existing of some features in Advanced Detector which are geared towards resolving such conflicts.

In the running mode Advanced Detector tries to match as many information stored in the config game entry as possible. Typical keys it matches against are '''gameid''', '''platform''' and '''language''', but it may also use '''extra''' when instructed to do so.

In case there are no matches in the ''ADGameDescription'' list, there are two additional fallback detection modes. One is file-based detection, which matches just the file names, and second one is a hook which gets called and could contain code of any complexity. Most prominent example of advanced fallback detection is SCI engine.

The target generation is highly affected by AD flags. The flags which have influence are: ADGF_CD, ADGF_DEMO, ADGF_DROPLANGUAGE.  

This table contains all gameids which are known by the engine. Also each gameid contains full human-readable description, which goes to '''description''' field in ScummVM configuration file.

Only '''gameid''' which are present in this table could be used in ''ADGameDescription'' table.

Please note that it is NULL-terminated, and also contains generic gameid ''cine'' which is used by fallback detection.

'''gameid''' -- This is gameid. Mainly it is used for taking the game description from ''PlainGameDescriptor'' table.

'''extra''' -- This is used to distinguish between different variants of a game. The content of this field is inserted in the generated '''description''' for the config file game entry. In case '''kADFlagUseExtraAsHint''' ADFlag is set, contents of this field is stored in config file, and is used to additionally distinguish between game variants. In case '''ADGF_USEEXTRAASTITLE''' game flag is set, contents of this field will be put into '''description''' rather than one extracted from 'PlainGameDescriptor'' table.

'''filesDescriptions''' -- list of individual file entries used for detection. 13 files (last is zero terminated) is the max number of files used in ScummVM currently. We are forced to specify hardcoded number due to C++ limitation for defining const arrays.

'''platform''' -- platofrm of the game variant

Game flags are used to tell the engine which features this particular game has. There are both engine-specific and Advanced Detector-specific game flags. The latter besides being more or less universal also affect the detection behaviour.

'''ADGF_ADDENGLISH''' -- Used for dual language games. In this case user will be present with selection between localised and English version of the game. Affects GUIOs.

'''ADGF_DROPLANGUAGE''' -- generated target will not have language specified. Used mainly for multilanguage games which have language selector internally. Thus the language will be selected within the game and the setting stored in the config file, but the game entry will stay intact.

There are known hacked variants for some of the games exist in the wild. We used to ignore user reports on them, but with the number of engines growing it became tough to remember that this particular game is really a hack. If it is widespread enough, we were getting recurrent reports that the game is not detected. To avoid this situation we now accept md5s of such games but mark them accordingly.

'''ADGF_TESTING''' -- Specifies game which was announced for public testing. The user will get relevant warning when launching the game.

'''ADGF_UNSTABLE''' -- Specifies game which is not publicly supported and is in a heavy development. The user will get relevant warning when launching the game.

'''kADFlagUseExtraAsHint''' -- Specify this flag in situation when there are more than single game stored in the same directory. E.g. there is no way to know which game the user wants to run without asking him. The typical example is VGA version of ''Lure of the Temptress'' which contained both EGA and VGA datafiles in game directory.

Is a generic MetaEngine wrapper aware of Advanced Detector. It should be used whenever AD is used.

'''descs''' is pointed to list ''ADGameDescription'' structures, or their supersets.

'''gameids''' is pointed to list of ''PlainGameDescriptor'' structures defining supported gameids.

'''_md5bytes''' -- number of bytes used to compute md5. If set to 0 then whole file will be used. Beware of long files though since that can dramatically slow down the detection. Typically sane value is 5000 bytes, but often experiment is required for many game variants with subtle differences.