-- This function is called periodicly for each sound making entity
-- x,y is the position of the entity
-- Px, Py is player pos
-- Ent is the entity id (e iow) and num is the sound slot number
-- minVolume & volModifier are  set to appropriate values, i.e. canopy open volModifier is 0, when
-- closed I set it to 13 to muffle the sounds.
-- minVolume is the squared distance at which the sound cuts off, I use 4000 * 4000.

local function SetVolume(Ent, num, x, z, Px, Pz)
    local dx, dz = Px - x, Pz - z
    local sqDist = dx*dx + dz*dz

    local vol = minVolume - sqDist
    if vol > 0 then
        vol = 60 + (37 * (vol / minVolume)) - volModifier
    else
        vol = 0
    end
    SetSound(Ent, num)
    SetSoundVolume(vol)
end