These overlays (sometimes known as bezels) display art on top of the game you're playing. To use them, you need a PC or Raspberry Pi (or other compatible system) running some version of MAME and the associated game software, as well as a widescreen (16x9) monitor mounted vertically. To display the overlay while playing a game, download the artwork file for that game overlay (it must have the same filename as the game), place it in the Artwork folder within your MAME directory and launch the game. (For instance, the software for the game Magic Sword is called msword.zip, so it requires a file in the Artwork directory also called msword.zip.)
All overlays are 4K resolution (2160 x 3840), and listed dimensions are for the game screen, relative to a 4K vertical monitor. The actual game screen size will depend on the resolution of your monitor.
Most of the overlays include multiple presets that let you choose the size of the game screen, access a "dark" version designed to look more like a dark arcade, and sometimes other options. To choose a preset, press Tab while running the game to bring up the MAME menu, select Video Options, and select a preset from the list.
Some overlays include Curved presets designed with a curved screen port, to better simulate the look of a CRT monitor. These presets work best if you are using a geometry shader that adds a curved look to the game screen. For an optimal experience, you may need to adjust your shaders to match the curvature of the screen shape in the overlay. If you are not using a geometry shader, you are using a shader that adds a curved bezel, or if you prefer a rectangular screen port, choose a Straight preset where applicable.
Splat! is similar in many ways to Atari’s Food Fight, albeit as a two-player, two-joystick setup akin to Robotron: 2084. Where Food Fight goes cute, however, Splat! goes a bit dark — being hit by flying food causes your head to pop off and roll around the playfield, requiring you to retrieve it to continue fighting (how you find your head without a head is never really revealed). Another odd aspect is the game’s “Nerd Hunt” levels, which have you pelting hapless dorks with food (as a lot of the people hanging out in arcades in the 80s were nerds, it’s not clear who exactly this game was aimed at). Though it was never widely released, Splat! is a fast-paced and fun two-player messfest, so if you missed it in arcades, now's your chance to throw a few tomatoes.