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Generated water material map of Hyrule Main Field
Generated water material map of Hyrule Main Field

water.extm files describe the water heightmap and the texture of the main field and add-on content field.

water.extm File Specification

water.extm File Layout

Each file contains a 64×64 grid. For each vertex there is 8 bytes of data that describe the height of the mesh, the material type and flow speed.

Water Map Data

Each entry in the water data table is 8 bytes long.

Offset (h) Size Data Type Description
0x00 2 Unsigned Short height (Vertex y component)
0x02 2 Unsigned Short xAxisFlowRate
0x04 2 Unsigned Short zAxisFlowRate
0x05 1 Unsigned Byte materialIndex + 3. This may act as a checksum?
0x06 1 Unsigned Byte materialIndex

height and flowSpeed are stored as unsigned shorts, but seem to map to float values. These can be calculated by dividing by the max size of an unsigned short:

32767 / 0xffff = 0.5

height is further multiplied by another constant to get the final height (the constant is unknown at this time, but is close to 0x300 / 0xffff).

x and z[1] can be calculated, while iterating through the data table:

for (int index = 0; index < 256 * 256; index++) {
    uint x = index % 256;
    uint z = index / 256;

Flow Rates are calculated as (flowRate * 2) - 1 and ranges from -1 to 1. On the x-axis this changes flow direction from East (-1) to West (+1) and on the z-axis from North (-1) to South (+1).

Material Index

This data is stored in Terrain.Tex1.bfres.

id file name attribute attribute_sub flag Google Translated
0 Water Water Water 0 Water
1 HotWater 熱湯 Water Water_Hot 0 Hot water
2 Poison 毒水 Water Water_Poison 0 Poison water
3 Lava 溶岩 Lava Lava 0 Lava
4 IceWater 冷たい水 Water Water_Ice 0 Cold water
5 Mud 泥沼 Bog Bog 0 Bog
6 Clear01 透明水01 Water Water 0 Clear water 01
7 Sea Water Water 0 Ocean
  1. z is expected to be an integer quotient. The floor function can be used if integer division is not supported.