I recommend to use the WinSCP (https://winscp.net/eng/download.php) and putty (http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html) to manage and edit files on RPi.
You can watch this tutorial to set up winscp and putty:
After that you manage to go this folder: /opt/retropie/configs/
you can find a lot of folders inside, each one has a retroarch.cfg that has all settings.
The file /opt/retropie/configs/all/retroarch.cfg has the that configurations affects all platforms, but if you wanna change the specific platform for example megadrive, you need to edit the file /opt/retropie/configs/megadrive/retroarch.cfg
The easy way:
Download the files I put into dropbox (except psd file) and put them inside this folder “/opt/retropie/configs/megadrive/”
and edit the file “/opt/retropie/configs/megadrive/retroarch.cfg”
and add this code line
#include = "/opt/retropie/configs/megadrive/megadrive_video_settings.cfg"
right before the line
#include = "/opt/retropie/configs/all/retroarch.cfg"
Inside of pillarbox folder you can find out each overlay followed with a specific cfg file, to choose the specific overlay you need to edit the file “megadrive_video_settings.cfg” and edit the line
input_overlay = /opt/retropie/configs/megadrive/pillarbox/sega_scanlines.cfg to point it out the location of the wanted overlay.
To make your own Overlays:
download the PSD file (requires photoshop to open it), which as all mesures and indications to make your own, including the “filters” alike scanlines and such, all you have to do is import the images that you want and cut them next the guides, and export it as PNG file to maintain the opacity.
that PSD file works for CPS1, CPS2, CPS3, NeoGeo, PSX, NES, SNES, MegaDrive, PCEngine, yet some other platforms has different resolutions alike some arcade machines and MasterSystem and so on.
Each overlay must be followed with their own .cfg file, those files must contain:
overlays = 1 overlay0_overlay = overlay_name.png overlay0_full_screen = true overlay0_descs = 0
after that you need to edit the specific retroarch.cfg of the wanted platform and add the lines:
input_overlay_enable = true input_overlay_opacity = 1.0 input_overlay_scale = 1.0 input_overlay = /path/to/the/overlay_name.cfg
Any question feel free to ask