deepgrain-foundry/docs/DESIGN.md

# Design

What Deepgrain Foundry is meant to be, how its systems fit together, and the decisions made so
far with their reasons. Read the relevant part before changing how the game plays. When the owner
decides something new, add it under "Decisions" with the date.

## What the owner wants (stated by the owner)

- A **Sandustry-style factory and automation game**. Every cell is a fine falling-sand grain
  (one or two screen pixels at normal zoom), not a Terraria-size tile. The world is a
  Terraria-like side view with dark caves.
- **Strictly a factory game.** No RPG elements, no enemies, and no character items besides the
  dig and build tools.
- **Real physics, and player-built machines** instead of magic converter buildings. Furnaces are
  built from blocks, metal is cast in molds, and heat, air and gravity do the work. Physics
  hazards (heat, molten metal) damage builds only.
- **Loose material falls; solids hold.**
- **Copy and paste of builds.** Pasting places ghosts that the bot builds from the bag.
- **Tool upgrades are earned in a satisfying, not tedious way**, not bought with arbitrary
  credits. So far that means casting them: a drill bit in a Bit mold, a bigger bag in a Tank mold.
  The owner wants the whole upgrade system redesigned (see NOTES.md).
- **A hovering bot that flies freely.** A limited bag that can be upgraded.
- **An economy instead of a rocket or other final goal.**
  - Sell materials at the trade dock; refined goods and alloys pay more.
  - Spend the money on buildings.
  - Pay off the $20,000 land claim, then keep growing.
  - A milestone ledger marks progress.
- **Machines run without power**, for simplicity. The power code (water wheel, shaft, steam
  engine) is still there but switched off (`POWER_FREE` in `src/sim/pieces.js`). Those pieces are
  hidden from the menu, and old saves keep them.
- **Look.** Not pixel art. The default is the "smooth look": a smooth, illustrated style with
  soft, clay-like lighting, drawn by WebGL2. The pixel look stays as an option and is what tests
  use.
- **A water cycle, not springs.** Steam rises into clouds and comes back as rain, or as snow
  where it is freezing.
- **Sound.** Generated ambient music that changes with depth, and retro chiptune effects.
- **No external assets.** Everything is drawn and synthesized in code.
- **Controls and settings.** Modern keyboard and mouse, plus gamepad support, and plenty of
  graphics and display settings.
- **Platform.** A web game for now, built and tested by agents locally. A Rust version may come
  much later, for performance; keeping `src/sim/` free of the DOM keeps that open.

## The core loop

1. Dig with the resonance drill. Rock shatters into loose grains: rubble, ore, coal, clay, sand.
2. Vacuum up what you want (tick materials to take only those), and blow it out where you need it.
3. Build a furnace from wall blocks, with a grate floor over a mold. Charge it with ore and coal,
   light it, and let the molten metal run into the mold.
4. Bars drop out of the bottom of the mold; collect them and sell them at the trade dock, or fill buyers' orders, which pay more.
5. Better bits (copper, then iron, then steel) open harder rock: granite, then basalt. Deeper
   ores give tin, zinc, silver and gold, and alloys (bronze, brass) pay more.
6. Automate with belts, screw tubes, filters, fans, pipes and machines. Pay off the claim.

## Systems in brief

Details and numbers live in the code and in `docs/systems/`.

- **World:**
  - sizes 2048×1024, 3072×1280 or 4096×1536 grains;
  - layers: soil, stone, granite and basalt over a magma sea;
  - ores by depth:
    - coal, copper and clay near the top;
    - tin in the upper stone;
    - iron from about a quarter of the way down;
    - zinc in the middle (stone and granite);
    - silver deep in the granite;
    - gold deepest (granite and basalt);
  - ambient temperature falls with height and rises with depth.
- **Materials:** 95 material ids, counting air and a few used for built parts. Each is in a
  phase: solid, powder, liquid, gas, or item (bars).
  - Heat flows between cells. Things melt, freeze, boil, burn and react.
  - Fire needs air: a buried fire chokes, and a fan blowing in makes it hotter.
  - Coal burns at about 1350°C in still air and about 2000°C with a fan.
- **Drill:** see `docs/systems/dig-tools.md`. Pulse widths, tuning to one material, hardness by
  bit tier.
- **Building:** a 4×4-grain block grid.
  - Blocks: walls of any of several materials, belts, screw tubes, filters, grates, gates,
    pipes, pumps, outlets.
  - Machines: fan, Refiner, Stone cutter, Silo.
  - Molds: ingot, bit, tank. Ingot bars drop out of the bottom onto whatever is under the mold;
    leave one open block below and a belt under that carries them off. Ingot molds empty themselves:
    junk and mixed scrap drop below, slag is thrown away and the grate above is raked. Short stubs
    stay for the next firing. Removing any mold returns its set metal to the bag: whole bars as
    bars, the rest as scrap.
  - Build actions: drag for lines, Shift-drag for rectangles, hold G to replace, hold C / X and
    drag to copy / cut, V to paste, Ctrl+Z to undo, middle mouse to pick,
    Shift+Q/E to switch build tabs.
- **Economy:**
  - The trade dock pays for anything dropped through its grate, at the market price.
  - Prices dip when you sell a lot of one thing and recover over minutes.
  - Up to 3 orders at a time pay well over market. Builders' orders want bulk rubble, gravel,
    sand or stone bricks.
  - You start with $250 and $20,000 of claim debt.
- **Weather:** steam in the open sky becomes clouds. They drift and rain, or snow when cold.
  The world's water is counted, so rain only returns what evaporated.
- **Waste rock and liquids:** see `docs/systems/stone-and-liquids.md`. It covers the Refiner,
  pipes, the silo, glass bricks, the stone cutter and builders' orders.

## Decisions

The newest are at the bottom. The dates are when the decision was made or built.

**Up to 2026-10-19** (early design, stated by the owner): everything in "What the owner wants"
above, including:
- the economy replacing a rocket goal;
- machines without power;
- the smooth illustrated look;
- the water cycle instead of springs;
- testing in the pixel look unless graphics are being checked.

**2026-10-19 / 20, dig tools.** The resonance drill replaced the old drill. See
`docs/systems/dig-tools.md`.

**2026-10-22:**
- **Rock too hard for your bit never crumbles, however small.** Crumbling it to ore would give ore
  without the right bit and confuse players. Crumbling it to stone would lose ore. Instead, world
  generation makes no tiny hard specks: pieces of 30 grains or fewer become the rock around them,
  and older saves are cleaned once on load. Iron and zinc veins are fewer and chunkier, with the
  same total ore.
- Belts and filters next to each other look like one belt. Belt ends are square with rounded
  corners.
- Dragging belts or filters sets their direction from the drag. R sets it when placing without
  dragging. An arrow shows the direction while dragging, and the selection card names it.
- **Copy and cut** are held keys, not a tool. Hold C or X and drag a box; it acts on release.
  Copy and cut look different. Cut is destructive, but it can be pasted back or undone.
- **Ctrl+Z undoes building** (up to 80 steps). The bot building ghosts is never a step of its own.
- **Holding Ctrl** while placing replaces what is built there (moved to G on 2026-10-23).
- **Fans melt like copper (1085°C).** Put the fan outside the furnace, blowing in through a grate.
  The game warns when a fan gets close to melting.
- **The vacuum takes only ticked materials** when anything is ticked, even if the drag starts on
  something else.
- **The Refiner** grinds stone, granite and basalt rubble, gravel, sand and dirt for trace ore,
  roughly halving the waste. Ore and anything else it cannot grind drop straight through.
- **Pipes, pumps and outlets** move liquids up to 500°C, one liquid per line. A line is stored as
  a count, not simulated grains. Water in pipes counts toward the world's water, so the weather
  does not replace it.

**2026-10-23:**
- **Ingot molds drop bars below automatically.** The owner reported bars being thrown into the
  furnace above and wants belts underneath to carry them off. Blocked bars wait in the trough;
  short stubs stay for the next firing. The mold cleans itself and rakes the grate after dropping bars or clearing junk.
- **Screw tubes carry no more than belts:** they move every other tick. For more throughput,
  build more lines.
- **A heap on a belt moves as one**, up to 96 grains deep, not just its bottom layer. If a grain is blocked,
  the load above it stands still and the belt slips underneath; the top no longer slides over
  a stuck bottom. Filters still let their chosen materials drop through.
- **Pick** (middle mouse) selects the piece under the cursor with its direction,
  wall material and filter settings. G no longer picks, as the owner requested (it is now Replace).
- **The build menu** is a bar of tabs and icon tiles along the bottom: Structure, Moving,
  Liquids, Machines, Molds. Hover a tile for its full description, cost and placement help;
  gamepad players see the selected tile’s popup. While building, the top-left card describes
  the build tool and shows the R/F settings, Replace, ghosts and status.
- **No length limit when dragging.** Blocks out of the bot's reach become ghosts that it builds
  when it gets there.
- **Pipes are thin:** sand, water and anything else loose passes them. Pumps and outlets are
  solid.
- **Uses for waste rock and sand:**
  - glass bricks (sand melted with a fan furnace, cast in an Ingot mold);
  - a Silo for storing one loose material, which should look like a real silo, not a magic
    black hole;
  - builders' orders for bulk rubble, gravel, sand and stone bricks;
  - a Stone cutter that makes stone bricks, which build cut-stone walls.
- **Rubble sells for a pittance** ($0.02 a grain, gravel $0.03). Dirt still earns nothing.
- **Re-refining sand stays allowed.** Refiner sand can be refined again, even in stacked
  refiners until none is left. The owner's reason: it is less profitable than making glass, so
  players will do it only when they need more ore rather than more money.
- The project moved from a claude.ai artifact to local development with coding agents. It is
  built from small files, with `NOTES.md` as the owner's to-do inbox.
- **Replace is held G, not Ctrl.** The owner hit the browser's Ctrl+W (close tab) and Ctrl+D
  (bookmark) while replacing and flying with WASD, and the game ignored WASD while Ctrl was held.

- **The build tool's top-left card describes the build tool**, like the other tools' cards:
  how to place, the build keys, the R/F settings (material, direction, filter), Replace · G and
  ghosts waiting. The selected piece's name, cost and description are in the menu and its hover
  popup. The owner asked for a general description rather than the selected building.
- **Ingot molds need no F.** They push junk and mixed metal out of the bottom as loose grains with the bars, throw slag away and rake the grate. Removing any mold returns its set metal: whole bars as bars, the rest as scrap. The owner asked what F was for once bars dropped on their own, and chose this over keeping F for cleaning.

- **Fewer, smaller messages.** Molds show only a small percentage, red when blocked or spoiled and gold when a casting waits for F; details are in the hover panel. Bars dropping, blocked molds and set castings no longer pop up cards or toasts. Fan heat is a red marker on the fan; melted tubes and machines get a short red label where they were. Status lines are one short sentence. The owner found the messages too large and too many.

- **World sounds are local.** Sounds from the world (water sizzling on hot metal or lava, and
  any other event with a place) are heard around the bot, whatever the zoom: full volume within
  24 grains, fading to silent at 96, panned left or right. The owner heard a constant snapping
  that followed the bot in an older world but not in a new one. It was the sizzle: in the
  owner's world, water that had found its way down to hot basalt and granite (480-800°C, about
  500 grains below the surface) boiled about 48 times a minute, every one at full volume. The
  first fix faded sounds with distance from the view; zoomed out they were still heard, so the
  owner asked for a radius around the bot instead.
- **The silo has pixel art in the pixel look**, drawn grain by grain like the rest of the world;
  the smooth look keeps the illustrated silo. The owner noticed it looked the same in both.

- **Screw tubes use all their lanes.** Grains in an up or down tube shift sideways toward the
  emptier lanes of the block, and grains taken in from the side go to the far lanes first. A
  block-wide lift fed by a belt from the side now carries about 90% of what the belt brings
  (before, only the edge lane filled: the owner saw one line on either side). Belts keep their
  speed.
- **Screw tubes carry bars**, one whole bar at a time, in line with the grains: a belt pushes a
  bar into a tube's side, it rides through corners and leaves the mouth. The owner asked how bars
  should be moved and chose tubes over a separate bar lift.
- **Several worlds are kept.** Each world has its own save and autosave; the title screen's Worlds
  list loads, renames and deletes them, and a new or imported world never overwrites another. An
  old single save becomes 'World 1'. The owner asked for multiple saves.

## Ideas not built yet

- **Concrete**, as a stronger wall material from rubble.
- **Upgrade ideas for the drill**: an amplifier, a tuning fork, harmonics. Also a Grav pick
  upgrade tool and mining charges. See `docs/systems/dig-tools.md`.
- The owner's ideas for later are in the "Future features and ideas" section of `NOTES.md`.