Thread by @sylefeb

The DooM-chip! It will run E1M1 till the end of times (or till power runs out, whichever comes first).
Algorithm is burned into wires, LUTs and flip-flops on an #FPGA: no CPU, no opcodes, no instruction counter.
Running on Altera CycloneV + SDRAM. (1/n)

Everything is described in a language I am working on: SDRAM controller, divider, BSP traversal, texture unit, etc.
Main renderer (w/o data) is 666 lines of code (!).
A great test case, made quite a few improvements, fixed some issues, learned a lot on CycloneV + Quartus.
(2/n)

Rendering uses the original BSP tree (of course!) but is modified to better fit a hardware implementation ; columns are raycast and drawn immediately front-to-back, stopping as soon as fully filled.
(3/n)

fabiensanglard.net/doomIphone/doo…

A nice property is that a column always grows from top and bottom towards its middle when drawn during front-to-back BSP traversal, until an opaque wall is reached.
(4/n)

Used several sources of information ; the excellent Doom black book by @fabynou (where I learned the colormap trick for lighting - so elegant!!), the Unofficial Doom Specs v1.666, and of course the original source code:
github.com/id-Software/DO…
(5/n)

Uses true game data ; the Lua preprocessor extracts the data from the Doom WAD during compilation, and writes tables and hardware for the level.
(6/n)

Getting floor and ceiling texturing right was not so simple, as the computations differ from walls. Here is a debug view of color coded distance from viewer, ensuring computations match for both.
(7/n)

Many things to improve + optimize: parallelize columns, hide latency between drawing, texture mapping and BSP traversal. Some textures misaligned, some glitches to fix (below: debug in progress). Also runs at 320x200 60Hz instead of 70Hz! (sorry @fabynou, not fixed yet!)
(8/n)

Doom was released as I was learning how to code graphics. It was, and remains, an immense inspiration and motivation boost. I spent countless hours making levels, hacking the game and hex dumps of doom.exe / doom.wad. This was a good opportunity to dive back into it!
(9/n)