Island code

The game exports and imports islands as a text code (IslandGrid.ExportIsland / ImportIsland). The format below was decoded from the game code and checked by round-trip (encode, decode, encode again gives the same bytes).

Encoding layers

1. The code is base64 text.
2. The bytes are raw DEFLATE (no zlib header).
3. The inflated bytes are a stream of packed integers (the MLAPI packing) holding a IslandGrid.SyncData.

Packed integers

Each integer is zigzag encoded and written as a variable-length 64-bit value:

SyncData content

In order:

• buildings[] and remains[]: each entry has typeId, x, y, orient, mirror, health, a nullable disaster (a flag and two 64-bit payloads) and turn.
• groundTiles: run-length encoded.
• natureTiles: run-length encoded, -1 means no nature object.
• innerCliffs[]: a count, then seven packed integers per entry.

The grid side is the square root of the ground tile count (49 by default).

Building footprints

The shape of a building is BuildingType.localPositions (an int2[]). orient rotates it in steps of 90 degrees and mirror flips the x axis:

orient 0..3 -> (cos, sin) = (1,0) (0,1) (-1,0) (0,-1)
x' = (dx * cos - dy * sin) * scaleX        scaleX = -1 when mirrored, otherwise 1
y' =  dx * sin + dy * cos
world position = building position + (x', y')

Ground and nature ids

Ground tile ids seen in the disaster code: 1 is skipped by a meteorite, 4 has inner cliffs that a meteorite removes, and 5 is scorched earth (what a meteorite leaves).

Building types (version 1.0.4)

The ids are the indices in BuildingTypes.Types, in save-file order.

Docks, Fishing Ships and Lighthouses may stand on water (localPositionsInWater). Maximum health examples: Castle 200, Wonder 150, Dock 50, House 15. A castle placed on the very edge of the island does not appear.