Callback: Custom profit calculation for cargoes

Custom profit calculation for cargoes (39)

This callback is called every time cargo is delivered to a station, to get how much income the player should get. The low word of var. 18 contains the distance of the transfer, byte 3 contains the amount of cargo moved and the highest byte contains the time spent en-route (a unit of time is +185 ticks, or ca. 2.5 days). The result should be a signed multiplier that gets multiplied by the amount of cargo moved and the price factor, then gets divided by 8192. Since the highest bit must always be set for a callback result, TTDPatch checks for the second highest bit (bit 14) for the sign. Returning a negative value means that the player has to pay for the transfer instead of getting money from it. For example, the maximum returnable value of 16383 means that the player gets twice the price factor for every unit.