MTADopplerEffect.lua

local map_setSoundProperty = {["SampleRate"] = 1, ["Tempo"] = 2, ["Pitch"] = 3, ["Reversed"] = 4}
function setSoundProperty(sound, property, value)
    -- Only handle sound elements
    if (not isElement(sound) or getElementType(sound) ~= "sound") then return end
 
    -- Get the current properties
    local properties = { getSoundProperties(sound) }
 
    -- Get the index by using the property parameter
    local index = map_setSoundProperty[property]
 
    -- Apply the value if there is an index for it
    if (index) then properties[index] = tonumber(value) end
 
    -- Return the property-success boolean
    return setSoundProperties(sound, unpack(properties))
end
 
function applyDopplerEffectToSound(sound)
    -- Get the receiver (use localPlayer if we have no vehicle)
    local receiver = { e = getPedOccupiedVehicle(localPlayer) }
    if (not receiver.e) then receiver.e = localPlayer end
   
    -- Get the sender (abort if it's invalid or if it equals to the receiver)
    local sender = { e = getElementAttachedTo(sound) }
    if (not sender.e or sender.e == receiver.e) then return end
 
    -- Receiver information
    receiver.p = { getElementPosition(receiver.e) }
    receiver.v = { getElementVelocity(receiver.e) }
 
    -- Sender information
    sender.p = { getElementPosition(sender.e) }
    sender.v = { getElementVelocity(sender.e) }
 
    -- Distance calculation (abort if there is no distance)
    local dx, dy, dz, d = getDistanceBetweenPoints(receiver.p, sender.p)
    if (d < 1) then return end
 
    -- Calculate velocity dotproduct for receiver and sender
    sender.vs = getVelocityDotproduct(sender.v, dx, dy, dz, d)
    receiver.vr = getVelocityDotproduct(receiver.v, dx, dy, dz, d)
 
    -- Calculate pitch
    local p = ((1 + receiver.vr) / (1 + sender.vs)) * (4.5 * math.max(0, sender.vs - receiver.vr))
    setSoundProperty(sound, "Pitch", p)
end
 
function getDistanceBetweenPoints(pointA, pointB)
    local x, y, z = math.abs(pointB[1] - pointA[1]), math.abs(pointB[2] - pointA[2]), math.abs(pointB[3] - pointA[3])
    local distance = getDistanceBetweenPoints3D(pointA[1], pointA[2], pointA[3], unpack(pointB))
    return x, y, z, distance
end
 
function getVelocityDotproduct(point, dx, dy, dz, d)
    if (d == 0) then return 1 end
    return (math.abs(point[1] * dx) + math.abs(point[2] * dy) + math.abs(point[3] * dz)) / d
end