BGFX Effects for (nearly) Everyone

Introduction

By default, MAME outputs an idealized version of the video as it would be on the way to the arcade cabinet’s monitor, with minimal modification of the output (primarily to stretch the game image back to the aspect ratio the monitor would traditionally have, usually 4:3). This works well, but misses some of the nostalgia factor. Arcade monitors were never ideal, even in perfect condition, and the nature of a CRT display distorts that image in ways that change the appearance significantly.

Modern LCD monitors simply do not look the same, and even computer CRT monitors cannot match the look of an arcade monitor without help.

That’s where the new BGFX renderer with HLSL comes into the picture.

HLSL simulates most of the effects that a CRT arcade monitor has on the video, making the result look a lot more authentic. However, HLSL requires some effort on the user’s part: the settings you use are going to be tailored to your PC’s system specs, and especially the monitor you’re using. Additionally, there were hundreds of thousands of monitors out there in arcades. Each was tuned and maintained differently, meaning there is no one correct appearance to judge by either. Basic guidelines will be provided here to help you, but you may also wish to ask for opinions on popular MAME-centric forums.

Resolution and Aspect Ratio

Resolution is a very important subject for HLSL settings. You will want MAME to be using the native resolution of your monitor to avoid additional distortion and lag caused by your monitor upscaling the display image.

While most arcade machines used a 4:3 ratio display (or 3:4 for vertically oriented monitors like Pac-Man), it’s difficult to find a consumer display that is 4:3 at this point. The good news is that that extra space on the sides isn’t wasted. Many arcade cabinets used bezel artwork around the main display, and should you have the necessary artwork files, MAME will display that artwork. Turn the Zoom to Screen Area setting in the video options menu to scale and crop the artwork so the emulated screen fills your display in one direction.

Some older LCD displays used a native resolution of 1280×1024 and were a 5:4 aspect ratio. There’s not enough extra space to display artwork, and you’ll end up with some very slight pillarboxing, but the results will be still be good and on-par with a 4:3 monitor.

Getting Started with BGFX

You will need to have followed the initial MAME setup instructions elsewhere in this manual before beginning. Official MAME distributions include BGFX as of MAME 0.172, so you don’t need to download any additional files.

Open your mame.ini file in your text editor of choice (e.g. Notepad), and make sure the following options are set correctly:

  • video bgfx

Now, you may want to take a moment to look below at the Configuration Settings section to see how to set up these next options.

As explained in Order of Config Loading, MAME has a order in which it processes INI files. The BGFX settings can be edited in mame.ini, but to take full advantage of the power of MAME’s configuration files, you’ll want to copy the BGFX settings from mame.ini to one of the other configuration files and make changes there.

In particular, you will want the bgfx_screen_chains to be specific to each game.

Save your INI file(s) and you’re ready to begin.

Configuration Settings

bgfx_path

This is where your BGFX shader files are stored. By default, this will be the bgfx folder in your MAME installation folder.

bgfx_backend

Selects a rendering backend for BGFX to use. Possible choices include d3d9, d3d11, d3d12, opengl, gles, metal, and `vulkan. The default is **auto**, which will let MAME choose the best selection for you.

  • d3d9 -- Direct3D 9.0 Renderer (Requires Windows XP or higher)

  • d3d11 -- Direct3D 11.0 Renderer (Requires Windows Vista with Direct3D 11 update, or Windows 7 or higher)

  • d3d12 -- Direct3D 12.0 Renderer (Requires Windows 10 or higher)

  • opengl -- OpenGL Renderer (Requires OpenGL drivers, may work better on some video cards, supported on Linux and macOS)

  • gles -- OpenGL ES Renderer (Supported with some low-power GPUs)

  • metal -- Apple Metal Graphics API (Requires macOS 10.11 El Capitan or newer)

  • vulkan -- Vulkan Renderer (Requires Windows or Linux with compatible GPU drivers.

bgfx_debug

Enables BGFX debugging features. Most users will not need to use this.

bgfx_screen_chains

This dictates how to handle BGFX rendering on a per-display basis. Possible choices include hlsl, unfiltered, and default.

  • default -- default bilinear filtered output

  • unfiltered -- nearest neighbor sampled output

  • hlsl -- display simulation through shaders

  • crt-geom -- lightweight CRT simulation

  • crt-geom-deluxe -- more detailed CRT simulation

  • lcd-grid -- LCD matrix simulation

We make a distinction between emulated screens (which we’ll call a screen) and output windows or monitors (which we’ll call a window, set by the -numscreens option) here. Use colons (:) to separate windows, and commas (,) to separate screens in the -bgfx_screen_chains setting value.

For the simple single window, single screen case, such as Pac-Man on one physical PC monitor, you can specify one entry like:

bgfx_screen_chains hlsl

Things get only slightly more complicated when we get to multiple windows and multiple screens.

On a single window, multiple screen game, such as Darius on one physical PC monitor, specify screen chains (one per window) like:

bgfx_screen_chains hlsl,hlsl,hlsl

This also works with single screen games where you are mirroring the output to more than one physical display. For instance, you could set up Pac-Man to have one unfiltered output for use with video broadcasting while a second display is set up HLSL for playing on.

On a multiple window, multiple screen game, such as Darius on three physical PC monitors, specify multiple entries (one per window) like:

bgfx_screen_chains hlsl:hlsl:hlsl

Another example game would be Taisen Hot Gimmick, which used two CRTs to show individual player hands to just that player. If using two windows (two physical displays):

bgfx_screen_chains hlsl:hlsl

One more special case is that Nichibutsu had a special cocktail mahjong cabinet that used a CRT in the middle along with two LCD displays to show each player their hand. We would want the LCDs to be unfiltered and untouched as they were, while the CRT would be improved through HLSL. Since we want to give each player their own full screen display (two physical monitors) along with the LCD, we’ll go with:

-numscreens 2 -view0 "Player 1" -view1 "Player 2" -video bgfx -bgfx_screen_chains hlsl,unfiltered:hlsl,unfiltered

This sets up the view for each display respectively, keeping HLSL effect on the CRT for each window (physical display) while going unfiltered for the LCD screens.

If using only one window (one display), keep in mind the game still has three screens, so we would use:

bgfx_screen_chains hlsl,unfiltered,unfiltered

Note that the commas are on the outside edges, and any colons are in the middle.

bgfx_shadow_mask

This specifies the shadow mask effect PNG file. By default this is slot-mask.png.

Tweaking BGFX HLSL Settings inside MAME

Start by loading MAME with the game of your choice (e.g. mame pacman).

The tilde key (~) brings up the on-screen display options. Use up and down to go through the various settings, while left and right will allow you to change that setting. Results will be shown in real time as you’re changing these settings.

Note that settings are individually changeable on a per-screen basis.

BGFX slider settings are saved per-system in CFG files. If the bgfx_screen_chains setting has been set (either in an INI file or on the command line), it will set the initial effects. If the bgfx_screen_chains setting has not been set, MAME will use the effects you chose the last time you ran the system.

Using the included pillarbox filters

MAME includes example BGFX shaders and layouts for filling unused space on a 16:9 widescreen display with a blurred version of the emulated video. The all the necessary files are included, and just need to be enabled.

For systems using 4:3 horizontal monitors, use these options:

-override_artwork bgfx/border_blur -view Horizontal -bgfx_screen_chains crt-geom,pillarbox_left_horizontal,pillarbox_right_horizontal

For systems using 3:4 vertical monitors, use these options:

-override_artwork bgfx/border_blur -view Vertical -bgfx_screen_chains crt-geom,pillarbox_left_vertical,pillarbox_right_vertical

  • You can use a different setting in place of crt-geom for the effect to apply to the primary screen image in the centre (e.g. default, hlsl or lcd-grid).

  • If you’ve previously changed the view for the system in MAME, the correct pillarboxed view will not be selected by default. Use the video options menu to select the correct view.

  • You can add these settings to an INI file to have them apply to certain systems automatically (e.g. horizont.ini or vertical.ini, or the INI file for a specific system).