{"id":76,"date":"2020-07-19T06:50:48","date_gmt":"2020-07-19T04:50:48","guid":{"rendered":"https:\/\/blogs.scummvm.org\/ar28\/?p=76"},"modified":"2022-04-15T06:54:24","modified_gmt":"2022-04-15T04:54:24","slug":"getting-a-better-understanding-a-little-progress","status":"publish","type":"post","link":"https:\/\/blogs.scummvm.org\/ar28\/2020\/07\/19\/getting-a-better-understanding-a-little-progress\/","title":{"rendered":"Getting a better understanding & a little progress"},"content":{"rendered":"

Hello! The first few days this week, I spent trying to understand my task, and work on a small number of engines, and try to make games detect\/work as a means to see if everything would work as expected. But first, some context.<\/p>\n

ScummVM has a MetaEngine and a Engine.<\/p>\n

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MetaEngine<\/h4>\n
A MetaEngine is responsible for, as the name would suggest, a meta-data related things before we actually start the engine. This is an abstract class, and each specific engine must inherit it and have their own implementation of it.<\/div>\n
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Alternatively, we also have an AdvancedMetaEngine, inheriting from MetaEngine, which provides a default Game Detection algorithm – which saves individual engine developers the hassle of providing detection tools. The detection algorithm is an Md5 + filename check and makes game detection easier for engines. These engines can inherit from AdvancedMetaEngine and provide some other metadata\/utility functions, like getting supported games, querying which features an engine has, etc.<\/div>\n
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AdvancedMetaEngine provides a means for engines to detect games. But, how does it know that a specific game belongs to a particular engine? Each engine provides a set of detector tables i.e a list of games it can support. Then, the default game detection algorithm checks each engine’s detection tables for a match. These files are often separated into a new file, and it is called “detection_tables.h”<\/div>\n
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So, each engine’s implementation of their own version of AdvancedMetaEngine (or MetaEngine) and other detection-related code is located in detection.cpp. This file includes the detection_tables header file, so the resulting object file generated has all the necessary information which it would need for detection.<\/div>\n
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Engine<\/h4>\n
An engine is the actual game engine, which is created when we try to run a game.<\/div>\n
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So, what is the task exactly?<\/h4>\n
I gave a very brief overview in my last post, but basically, the detection related code – which lives in detection.cpp, will need to be isolated in a way that actual detection related code goes to the executable, while the other kind of functions will be available as-is, on-demand at runtime.<\/div>\n
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So, the detector-tables, and other detection related code – like fallback detection moves in and is linked against the scummvm executable. So, the ScummVM executable depends on these (detection) object files.<\/div>\n
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Fallback detection is a way for engines to provide a means to find a “closest” match if the detector found no matches in the directory.<\/div>\n
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So, I have a little progress this week! It’s not much, but I worked towards the most basic thing as a few of small steps:<\/div>\n