Designing Games with Game Maker - YoYo Games

e careful how and when you apply it. Please keep these remarks in mind when you use any
of the following functions.
Different forms of motion planning are provided by Game Maker. The simplest form lets an
instance take a step towards a particular goal position, trying to go straight if possible but
taking a different direction if required. These functions should be used in the step event of an
instance. They correspond to the motion planning actions that are also available:
mp_linear_step(x,y,stepsize,checkall) This function lets the
instance take a step straight towards the indicated position (x,y). The size of
the step is indicated by the stepsize. If the instance is already at the
position it will not move any further. If checkall is true the instance will stop
when it hits an instance of any object. If it is false it only stops when hitting a
solid instance. Note that this function does not try to make detours if it meets
an obstacle. It simply fails in that case. The function returns whether or not
the goal position was reached.
mp_linear_step_object(x,y,stepsize,obj) Same as the function
above but this time only instances of obj are considered as obstacles. obj can
be an object or an instance id.
mp_potential_step(x,y,stepsize,checkall) Like the previous
function, this function lets the instance take a step towards a particular
position. But in this case it tries to avoid obstacles. When the instance would
run into a solid instance (or any instance when checkall is true) it will change
the direction of motion to try to avoid the instance and move around it. The
approach is not guaranteed to work but in most easy cases it will effectively
move the instance towards the goal. The function returns whether or not the
goal was reached.
mp_potential_step_object(x,y,stepsize,obj) Same as the function
above but this time only instances of obj are considered as obstacles. obj can
be an object or an instance id.
mp_potential_settings(maxrot,rotstep,ahead,onspot) The
previous function does its work using a number of parameters that can be
changed using this function. Globally the method works as follows. It first tries
to move straight towards the goal. It looks a number of steps ahead which can
be set with the parameter ahead (default 3). Reducing this value means that
the instance will start changing direction later. Increasing it means it will start