22.02.2015, 08:23
This is the beauty of sa-mp. It doesn't feed you all the systems by default. Often you will need to improvise. Store the locations of all vehicles. If they have a driver, ignore the vehicle until they no longer do and store it again if necessary and otherwise compare locations and trigger your own callback.
EDIT: If you want to be really fancy, create an object inside every vehicle using AttachObjectToVehicle and move that object WITH the vehicle - causing the callback to be triggered everytime it moves, however I am pretty sure you'll have to remove the attachment before hand and attach it afterwards again and this makes it a little complicated, but this way you can avoid checking the locations of vehicles all the time.
EDIT: If you want to be really fancy, create an object inside every vehicle using AttachObjectToVehicle and move that object WITH the vehicle - causing the callback to be triggered everytime it moves, however I am pretty sure you'll have to remove the attachment before hand and attach it afterwards again and this makes it a little complicated, but this way you can avoid checking the locations of vehicles all the time.