@casadero said in How do I add scanlines to MAME in retropie 4.2?:

@caver01 : correction to my recent post: I put the ROMs to the MAME-MAME4ALL folder and, later, to the ARCADE folder. there is no folder like "lr-mame2003" folder on my USB stick, but a "mame-libreto". I still do not know the difference between all these MAME Emulators, but I will start some research about that issue the coming weekend.

Please read this.

Emulators come in two basic flavors in RetroPie--standalone or libretro core. The standalone are just that--they run independently of other frameworks. They are configured independently. They might have their own way of generating display effects (advancemame for instance has some RGB effects that can be turned on). The libretro cores are all emulators that run inside of the RetroArch framework. These can share common settings for controls, video, etc. The CRT-PI shader is for RetroArch, so it won't apply to the standalone emulators, whether they are MAME or something else.

Given the two kinds of emulators, there are several different versions of MAME. Some are standalone, some libretro cores. Each requires their own ROM versions. Generally speaking, you should only use ROMs that come from a set with a version matching that version of MAME. If the location of your ROMs allows you to choose more than one emulator, you do that using the RUNCOMMAND function (which you should also click and read).