# Engine facts and limits

Numbers to design levels with, and the things that crash the game. Measured in the game with the
test harness unless noted.

## Scale and movement

One unit = one grid cell. Measured with the jump lab ([`levels/sprunglabor.py`](../../levels/sprunglabor.py))
and a coin measuring track ([notes/levelbau.md](../../notes/levelbau.md#findings-from-the-game-tests-lamatest-xvfb)):

| Quantity | Value |
|---|---|
| llama height | about 0.6 |
| walking speed | about 1.1 units/s (≈ 1 s to accelerate) |
| highest edge a jump clears | 0.35 (0.5 is too high) |
| long jump with a run-up | about 1.3 units (from standing: much shorter, a 0.5 gap fails) |
| comfortable parkour | gaps of 0.3 with +0.2 height, platforms ≥ 1.5 long |
| step-up without jumping | none – any edge with wall collision blocks; use slopes or walls without collision |
| frame rate of the logic | 30 frames per second (script speeds are per frame) |

Controls are **camera-relative**; the start camera sits behind the llama and moves aside if
something solid is right behind it – keep the area behind start points clear.

## Drawing

| Fact | Value |
|---|---|
| draw distance | = **fog end** of the active environment zone; originals 7–16 cells at detail *Maximum* (roller coaster up to 23), about half at *Minimum* |
| objects | drawn only within about **12.5 units of the llama** (they keep running); their activity radius also follows the fog end |
| hidden areas | visibility regions: a cell is drawn only if the camera region's mask contains its region |
| texture coordinates | none per vertex – every triangle shows half of a texture rectangle |
| lights | light only object models; tiles use baked vertex colours |

The *Draw distance* mod scales all fog values of all levels
([notes/mod-fog.md](../../notes/mod-fog.md)).

## Memory and counts

| Limit | Value | Source |
|---|---|---|
| level memory | **16 MB** for STPC, TEXT, TRAK, MAP, LGPC and the strat pool; originals use up to ~7 MB | `FUN_0041eea0` |
| strat heap | 65533 words (≈ 256 KB) for strat slots (0x154 bytes each), collision blocks and variables | `FUN_0041ae20` |
| strat slots | `poolExtra + 30` – must cover placed **and** spawned objects | MAP |
| vertices per tile model | 8000 (transform buffer) | |
| collision polygon | within ±8 units of its tile's origin | i16 fixed point |
| texture pages | 127 | signed page byte |
| texture entries | 65535 | u16 face field |
| sound samples | 128 per level | signed char id |
| file sizes that worked | TRAK up to 1 MB, 5800 tiles, WAD up to ~7 MB (originals); the test world: 628 models, 2474 tiles, 6.3 MB | measured |

## Things that crash the game

| Cause | Symptom |
|---|---|
| a tile outside the W × H grid | memory corruption, crash on load or later |
| vertex-colour block not exactly one entry per vertex | objects read shifted, crash |
| a strat type with collision but type flags 0 (or too few collision-bone words) | page fault in the heap allocator `FUN_0041ae20` |
| exit target (7, 7, 7) in world 9 | crash after saving (world 10 has no name) |
| a selectable chapter without a WAD | "Couldnt load wad" on the world map |
| a waypoint-dependent type without its boxes | not a crash: the game removes the object ("removing strat") |
| world-9 chapters 2–31 (unpatched exe) | progress, language or options overwritten ([TestLevel](testlevel.md)) |

## Coordinates, numbers, angles

* Game space: x east, y up, z = grid row; strats use 20.12 fixed point (4096 = 1.0).
* MAP angles: 4096 = 360°; strat angles: 0x1000000 = 360°.
* Objects on a flat original floor tile stand at `tile.y + 0.25`.