# Design rules

The numbers and rules that matter when you design a level for this engine. Background and sources:
[Engine facts and limits](../reference/engine-limits.md).

## Sizes to design with

| | |
|---|---|
| one grid cell | 1 unit |
| llama | 0.6 tall, walks 1.1 units/s |
| jump up | ≤ 0.35 (0.5 fails) |
| jump across, with a run-up | ~1.3 (from standing much less) |
| easy parkour | gaps 0.3 with +0.2 height, platforms ≥ 1.5 long |
| steps without jumping | none – use slopes or walls without collision |
| draw distance | the fog end of the zone: 8–16 cells in the originals |
| objects visible | within ~12.5 units of the llama |

![The Test World's gallery: every figure of the game on a pedestal](../img/testworld-gallery.jpg)

## Rules that keep the level working

1. **One player start**, with nothing solid right behind the llama (start camera).
2. **Exit = LevelDoor + floor with collision material 16 in the same cell.** Target (1, 9,
   chapter) in TestLevel – never (7, 7, 7).
3. **A death floor or death plane** under every place the llama can fall to.
4. **A checkpoint** before every hard part.
5. **TestLevel chapter 1 or 32–49** for new levels.
6. **Guards and box walkers need their waypoint boxes** (and guards an event bit someone sets),
   or the game removes them.
7. **Every area must be visible from where the camera is**: with visibility regions, check the
   masks (*Check for problems* reports regions nothing can see).
8. **Stay within the budget**: 16 MB level memory, 127 texture pages, 128 sounds – the import
   preview and *Check for problems* show where you are.

The editor and both level builders enforce the data-level rules (tiles inside the grid, vertex
colours, type fields, collision cells) automatically. *Check for problems* reports the rest.

## Good habits

* **Play-test often** (F5). The engine is unforgiving and a small change can stop the exit or
  hide an area.
* **Look at the originals.** Open an original level in the editor and see how it builds doors,
  cameras and enemy paths; the [debug view mod](../tools.md#debug-view) shows collision and
  invisible objects in the running game.
* **Keep levels compact.** Short sight lines hide the draw distance and keep the frame rate up.
* **Copy numbers** (speeds, parameters, waypoint fields) from original objects that already do
  what you want.