Show HN: KiDoom – Running DOOM on PCB Traces (mikeayles.com)
Walls are rendered as PCB_TRACK traces, and entities (enemies, items, player) are actual component footprints - SOT-23 for small items, SOIC-8 for decorations, QFP-64 for enemies and the player.
How I did it:
Started by patching DOOM's source code to extract vector data directly from the engine. Instead of trying to render 64,000 pixels (which would be impossibly slow), I grab the geometry DOOM already calculates internally - the drawsegs[] array for walls and vissprites[] for entities.
Added a field to the vissprite_t structure to capture entity types (MT_SHOTGUY, MT_PLAYER, etc.) during R_ProjectSprite(). This lets me map 150+ entity types to appropriate footprint categories.
The DOOM engine sends this vector data over a Unix socket to a Python plugin running in KiCad. The plugin pre-allocates pools of traces and footprints at startup, then just updates their positions each frame instead of creating/destroying objects. Calls pcbnew.Refresh() to update the display.
Runs at 10-25 FPS depending on hardware. The bottleneck is KiCad's refresh, not DOOM or the data transfer.
Also renders to an SDL window (for actual gameplay) and a Python wireframe window (for debugging), so you get three views running simultaneously.
Follow-up: ScopeDoom
After getting the wireframe renderer working, I wanted to push it somewhere more physical. Oscilloscopes in X-Y mode are vector displays - feed X coordinates to one channel, Y to the other. I didn't have a function generator, so I used my MacBook's headphone jack instead.
The sound card is just a dual-channel DAC at 44.1kHz. Wired 3.5mm jack → 1kΩ resistors → scope CH1 (X) and CH2 (Y). Reused the same vector extraction from KiDoom, but the Python script converts coordinates to ±1V range and streams them as audio samples.
Each wall becomes a wireframe box, the scope traces along each line. With ~7,000 points per frame at 44.1kHz, refresh rate is about 6 Hz - slow enough to be a slideshow, but level geometry is clearly recognizable. A 96kHz audio interface or analog scope would improve it significantly (digital scopes do sample-and-hold instead of continuous beam tracing).
Links:
KiDoom GitHub: https://github.com/MichaelAyles/KiDoom, writeup: https://www.mikeayles.com/#kidoom
ScopeDoom GitHub: https://github.com/MichaelAyles/ScopeDoom, writeup: https://www.mikeayles.com/#scopedoom
25 comments
[ 2.9 ms ] story [ 57.1 ms ] threadWas never quite sure if I should raw XY it or soft modem so I could decode on a web page on a handy device.
KiDoom I don't fully get. The website says "All components connected to a shared net; the PCB could be sent to a fab house (it just wouldn't do anything useful)" but I don't see any of the component pins hooked up in the demo video.
That got me thinking “I wonder if anyone has done this on an oscilloscope” and oddly I can't fine anyone who quite has. That DOOM objects are sprites and not actual 3D objects would limit the fidelity, but the scenery could be rendered at least. There are several examples of managing to use a high-speed scope as a low-res monochrome raster device (scanning like a CRT monitor does and turning the beam on & off as needed).
I did find an example of Quake being done on a scope the way I was imagining: https://www.youtube.com/watch?v=aMli33ornEU - as all objects are actual 3D models in Quake that even manages to give them some presence & shape.
EDIT: then I read the second half of this post and saw ScopeDoom! I'm surprised there are no earlier examples that are easy to find.
I've written my own s-expr library to inject footprints and symbols and it's a huge pain and flakey. I'd love to move to something a bit more fleshed out and official.
The part I love most is how many unrelated systems had to cooperate:
extracting geometry directly from DOOM’s drawsegs/vissprite internals
mapping sprite classes to physical component footprints
running real-time updates through KiCad’s object model without triggering full recompute
and then running the same vector stream to an oscilloscope via audio DAC
That’s a really clever chain of “use the tool for something it was never designed to do.”
ScopeDoom might end up being the more interesting long-term direction, vector displays force you to think about rendering differently, and there’s something poetic about DOOM being rendered as literal analog voltage traces.
If you ever take it further, the combination of:
faster DAC (or multi-kHz arbitrary waveform generator)
true analog persistence phosphor scope
and dynamic sprite simplification
…could get you surprisingly close to a smooth vector-shooter aesthetic.
Either way: great hack. The world needs more playful abuse of serious tools.