Callback: Ambient sound effects

Ambient sound effects (144)

This callback is a generic callback for feature 0C (new sounds) used for playing ambient sound effects.

The 15-bit return value is the sound effect number. Values from 0 to 72 (dec) are TTD's built-in sound effects, values beyond that refer to the sounds from Action 11.

To decide whether to play a sound, and what sound to play, Var.Action 2 variable 10 holds the following information:

• GRFv7 For GRF version 7 and below: THRRxxxt
• GRFv8 For GRF version 8 and above: xTHHRRtt

Field	Meaning
T	Tile class, 0=bare land, 4=trees, 6=water
HH	GRFv7 Height of north corner of tile (multiple of 8) GRFv8 Height of lowest corner of tile (multiple of 1)
RR	8 random bits
xxx	Reserved
tt	Bits 0..2: Terrain type: 0 normal (grass), 1 desert, 2 rainforest, 4 on or above snowline. Bits 3..5: GRFv8 Water class: 0 - undefined / land; 1 - sea; 2 - canal; 3 - river.

This callback must be enabled by bit 4 in action D var 9E.