There’s something magical about volumetric displays. They really need to be perceived in person, and no amount of static or video photography will ever do them justice. [AncientJames] has built a few, and we’re reporting on his progress, mostly because he got it to run a playable port of DOOM.

As we’ve seen before, DOOM is very much a 3D game viewed on a 2D display using all manner of clever tricks and optimizations. The background visual gives a 3D effect, but the game’s sprites are definitely very solidly in 2D land. As we’ll see, that wasn’t good enough for [James].

The basic concept relies on a pair of 128 x 64 LED display matrix modules sitting atop a rotating platform. The 3D printed platform holds the displays vertically, with the LEDs lined up with the diameter, meaning the electronics hang off the back, creating some imbalance.

Lead, in the form of the type used for traditional window leading, was used as a counterbalance. A Raspberry Pi 4 with a modified version of this LED driver HAT is rotating with the displays. The Pi and both displays are fed power from individual Mini560 buck modules, taking their input from a 12 V 100 W Mean-Well power supply via a car alternator slip ring setup. (Part numbers ABH6004S and ASL9009  for those interested.) Finally, to synchronise the setup, a simple IR photo interrupter signals the Pi via an interrupt.

The base contains a DC motor driving the platform with a 224:20 reduction ratio using a GT2 timing belt to help reduce noise. [James] reports that running at 700 RPM was the limit for the current version, giving an acceptable update frame rate. Too high, and the vibration and chassis flex was excessive. The base does little else other than house that power supply and support a 400 mm acrylic garden light dome. We wouldn’t want to run this without such protection, which might not even be enough.

There are quite a few details to consider in such a build. One is the need to reduce the angle of perception of the LED display using a 3D printed slat-type collimator in front of each unit. You only want to perceive the LEDs head-on, or the POV effect is ruined. However, most of the details are in the software.

To that end, [James] took the entire game logic of the ‘Doom Generic’ port, removing the code that renders the 3D parts of the scene. The 2D menus and in-game panels are rendered by projecting the image onto a cylinder. That was easy. [James] took a minimalist path for the room scenes, as fully solid walls looked too busy. The viewport automatically zooms into any ongoing battles, so monsters zoom into focus if nearby, but objects behind closed doors and too far around corners are discarded. No spoiler alerts! The models were lifted from Chello’s Voxel Doom mod, giving a fitting 3D upgrade to gameplay. This is an ongoing project, so we’ll keep track and report back!

We’ve reported on a few volumetric displays over the years, like this tiny one based on an OLED display. Even a volumetric CCTV system. But they can’t run DOOM. Speaking of which, here’s what it looks like ray-traced.

Thanks to [Keith] for the tip!

If there’s a reason that fancy holographic displays that respond to gestures are a science fiction staple, it’s probably because our current display technology is terrible. Oh sure, Retina displays and big curved gaming monitors are things of wonder, but they’re also things that occupy space even when they’re off — hence the yearning for a display that can appear and disappear at need.

Now, we’re not sure if [Maker Mac70]’s floating display is the answer to your sci-fi dreams, but it’s still pretty cool. And, as with the best of tricks, it’s all done with mirrors. The idea is to use a combination of a partially reflective mirror, a sheet of retroreflective material, and a bright LCD panel. These are set up in an equilateral triangle arrangement, with the partially reflective mirror at the top. Part of the light from the LCD bounces off the bottom surface of the mirror onto a retroreflector — [Mac] used a sheet of material similar to what’s used on traffic signs. True to its name, the retroreflector bounces the light directly back at the semi-transparent mirror, passing through it to focus on a point in space above the whole contraption. To make the display interactive, [Mac] used a trio of cheap time-of-flight (TOF) sensors to watch for fingers poking into the space into which the display is projected. It seemed to work well enough after some tweaking; you can check it out in the video below, which also has some great tips on greebling, if that’s your thing.

We suspect that the thumbnail for the video is a composite, but that’s understandable since the conditions for viewing such a display have to be just right in terms of ambient light level and the viewer’s position relative to the display. [Mac] even mentions the narrow acceptance angle of the display, touting it as a potential benefit for use cases where privacy is a concern. In any case, it’s very different from his last sci-fi-inspired volumetric display, which was pretty cool too.