Boot your own OS

Two BREAK issues on the bounce, so we're owed a proper MAKE. And this one's a bit personal: for the last few weeks I've been building an operating system. A small one — desktop, windows, a terminal, a tracker, a handful of games — called acid OS. Today you boot it, write an app for it, and then crash that app on purpose to see why the rest of the system doesn't care. It's free, it's open source, and you don't need to flash anything.

> this week in security

Three quick ones — and a theme you'll spot again in the project: keep things in separate boxes.

> beginner's corner

Today's project is all about apps that live in their own little box. Your phone already works that way — the trick is checking what each box is allowed to reach.

The project — boot your own OS

acid OS runs in a window on your Linux desktop, so nothing gets installed over anything. You'll boot it, give it a new app, then break that app and watch the OS shrug.

What you'll need: a Linux machine with a desktop (X11 or Wayland — any distro), about ten minutes for the first build, and a willingness to type cargo.

Prefer to grab the finished app? plasma.lua and plasma.app.toml — drop both into v3/apps/.

01Boot it

Install the build tools (Debian/Ubuntu shown — the Fedora and Arch lines are in the repo's README):

sudo apt install build-essential pkg-config libasound2-dev git curl
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
source "$HOME/.cargo/env"

Then grab it and run it:

git clone https://github.com/NorfolkHacker/Acid-OS-V3.git
cd Acid-OS-V3
cargo run --release --manifest-path v3/Cargo.toml -p acid-os

The first build takes a few minutes; after that it boots in seconds. Pick a screen size (or just wait three seconds) and you're on the desktop. Have a poke: Menu is top left, and the File Manager → Games folder has AcidStorm, Acid Invaders and a Tetris that will eat your evening. Stay in the top folder of the repo when you run it — acid OS finds its apps by a path relative to it.

02Bring the plasma back

Remember the plasma from issue #00 — four sine waves stacked into something that looks alive? We're giving it a home. An acid OS app is just two files in v3/apps/: a Lua script, and a tiny "manifest" saying what it's called and how big its window is.

v3/apps/plasma.app.toml

name = Plasma
w = 240
h = 176
desc = Issue #00's plasma, now an app

v3/apps/plasma.lua

local Plasma = AcidGame:extend("Plasma")
Plasma.TICK_MS = 40              -- 25 frames a second

local CELL = 4                   -- each "pixel" is a 4x4 block
local TOP = 16                   -- the title bar is 16px tall

function Plasma:on_create()
  self.w, self.h = acid_window_size()
  self.cx, self.cy = self.w // 2, self.h // 2   -- where the ripple starts
  self.t = 0
end

function Plasma:on_touch(x, y, pressed)
  if pressed then self.cx, self.cy = x, y end   -- drag the ripple about
end

function Plasma:on_tick()
  self.t = self.t + 0.08
  if not self:focused() then return end

  local t, cx, cy = self.t, self.cx, self.cy
  acid_begin_frame()
  acid_draw_window_frame(self:window_title())
  for y = TOP, self.h - 1, CELL do
    for x = 0, self.w - 1, CELL do
      -- the same four ripples as issue #00, stacked
      local v = math.sin(x * 0.04 + t)
              + math.sin(y * 0.03 - t)
              + math.sin((x + y) * 0.03 + t)
              + math.sin(math.sqrt((x - cx)^2 + (y - cy)^2) * 0.04 - t * 1.5)
      -- v runs from -4 to 4: turn it into a spot on the 256-colour wheel
      acid_fill_rect(x, y, CELL, CELL, AcidPalette.hue(math.floor(v * 32 + t * 20)))
    end
  end
  acid_draw_window_border()
  acid_end_frame()
end

Plasma:new():start()

Run it straight into the desktop:

cargo run --release --manifest-path v3/Cargo.toml -p acid-os -- --app plasma

The real thing: acid OS at 640×480, plasma window up front.

There it is — the plasma, in a window, in an OS. Click and drag inside it and the ripple follows you. What's going on:

• AcidGame gives you a heartbeat: on_tick runs every TICK_MS milliseconds, so you redraw the whole thing 25 times a second.
• There are no pixels to poke. acid OS's drawing is deliberately simple — rectangles, circles, text, lines. So every "pixel" is a 4×4 filled rectangle. That's 2,400 of them a frame, and it keeps up without breaking a sweat. The chunky look is a feature.
• AcidPalette.hue replaces #00's three-shifted-sines colour trick: give it any number and it hands back a bright colour from a 256-step rainbow, wrapping round forever.
• acid_begin_frame / acid_end_frame draw into a hidden copy and swap it in all at once, so you never see a half-painted frame.
• No rebuild. You didn't touch any Rust. Change the Lua, close the window, open it again — the script loads fresh from disk every time.

03Now break it (on purpose)

This is the bit I'm proudest of. Add one line at the top of on_tick — a loop that never ends:

  while true do end

Run it again. The plasma freezes… and about two seconds later its window just goes. Look in the terminal you launched from:

Acid OS v3: v3/apps/plasma.lua: stopped responding

Everything else — desktop, clock, any games you had open — carried on as if nothing happened. That's because every app gets its own Lua brain on its own thread, and the OS keeps a stopwatch on each one. Hog it for more than two seconds and you're out. (Try error("boom") instead and you'll get your own message in the same spot.) Real operating systems do exactly this, just with more paperwork — it's the same "one break-in, one room" idea as this week's news. Take the line back out before you carry on.

> your turn