known

zip contains region.xaero which is uncompressed binary
per file: 512x512 blocks or one MCRegion
any 2d-arrays are indexed [x][z], so serialized as z-then-x, unlike MC's usual x-then-z order
region contains 8x8 ChunksChunks
chunk contains 4x4 tiles
tile contains 16x16 pixels (block columns)
pixel contains overlays, blockState, biome, height, light, heightShade, colorType
overlay contains opacity, overlayBlockState, customColor

region:

prelude: 00ff
version: 00000001
loop over present chunks:
- byte chunkCoords (x << 4 | z)
- loop over tiles:
  - absent: int -1
  - present: dump pixels

pixel:

int pixelParams
not grass? => int blockState
overlays? =>
- byte numOverlays
- dump overlays
colorType == 3? => int customColor
hasBiome? => byte biome

pixelParams:

bit 0: notGrass
bit 1: hasOverlays
bit 2-3: colorType
bit 4-5: heightShade
bit 6: height in extra byte instead of param (not written, legacy?)
bit 7: isCaveBlock (always false?)
bit 8-11: light
bit 12-19: height
bit 20: hasBiome

heightShade:

val 0: normal
val 1: brighter
val 2: darker
val 3: uninitialized (renders as normal)

colorType:

TODO biomeStuff[0]

customColor:

TODO biomeStuff[2]

overlay:

int overlayParams
isWater? => int overlayBlockState
colorType == 2? => int customColour
opacity > 1? => int opacity

overlayParams:

bit 0: notWater
bit 4: opacity > 1
bit 4-7: light
bit 8-11: colorType