ES-DE/CONTRIBUTING.md

Contributing to EmulationStation Desktop Edition
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### Help needed:

There are many cards in the Kanban backlog that would be nice to implement. And for this, code contributions are very welcome. There may be a bug or two as well that needs fixing ;)

And to put it mildly, I'm confused regarding CMake, so help is needed in this area. Although the building and package generation works more or less correctly, there are some hacks and similar in the CMakeLists.txt files that need improving by someone who really knows how this software package works.

Apart from code commits, help is especially needed for thorough testing of the software and for working on the rbsimple-DE theme.

It's impossible for me to test every game system (rbsimple-DE has support for more than a 100 different systems!) so it would be especially useful to hear about any issues with starting games using the default es_systems.cfg configuration file and also if there are any problems with scraping for certain systems.

And it's a fact that some configuration is simply missing in these files for some systems, so that would need to be added as well.

In general, a review of the [es_systems.cfg_unix](resources/templates/es_systems.cfg_unix), [es_systems.cfg_macos](resources/templates/es_systems.cfg_macos) and [es_systems.cfg_windows](resources/templates/es_systems.cfg_windows) files including the supported file extensions would be great.

As for rbsimple-DE there are quite some missing graphic files and other customizations for a number of game systems. Check out [MISSING.md](themes/rbsimple-DE/MISSING.md) for more details of what needs to be added or updated.

### Coding style:

The coding style for EmulationStation-DE is mostly a combination of the Linux Kernel style (although that's C it's close enough to C++ as far as I'm concerned) and Google's C++ guidelines.

Please refer to these documents here:

https://www.kernel.org/doc/html/v4.10/process/coding-style.html \
https://google.github.io/styleguide/cppguide.html

**Some key points:**

* Column width (line length) is 100 characters
* Indentation is 4 spaces, don't use tabs as they can be interpreted differently
* Line break is Unix-style (line feed only, no carriage return)
* Do not leave trailing whitespaces at the end of the lines (a good source code editor should have a setting to automatically trim these for you)
* When breaking up long lines into multiple lines, consider what could be useful data to grep for so you don't break in the middle of such a string
* Comments always in C++ style, i.e. // instead of /* */
* Comments should be proper sentences, starting with a capital letter and ending with a dot
* Use K&R placements of braces, read the Linux Kernel coding style document for clarifications
* Always use spaces between keywords and opening brackets, i.e. `if ()`, `for ()`, `while ()` etc.
* Indentation of switch/case statements is optional, but it's usually easier to read the code with indentations in place
* Use `std::string` instead of `char *` or `char []` unless there is a specific reason requiring the latter
* Actually, try to use C++ syntax in general instead of C syntax, another example would be `static_cast<int>(someFloatVariable)` instead of `(int)someFloatVariable`
* If the arguments (and initializer list) for a function or class exceeds 4 items, arrange them vertically to make the code easier to read
* Always declare one variable per line, never combine multiple declarations of the same type
* Name local variables with the first word in small letters and the proceeding words starting with capital letters, e.g. myExampleVariable
* Name member variables starting with a small 'm', e.g. mMyMemberVariable
* Use the same naming convention for functions as for local variables, e.g. someFunction()
* Inline functions makes perfect sense to use, but don't overdo it by using them for functions that won't be called very frequently
* Never put more than one statement on a single line (there are some exceptions though like lambda expressions and some switch statements)
* Avoid overoptimizations, especially if it sacrifices readability, makes the code hard to expand on or is error prone
* For the rest, check the code and have fun! :)

### Building and configuring:

Please refer to the [INSTALL.md](INSTALL.md) file for details on everything related to building EmulationStation Desktop Edition.