SOLVED issue with mp_potential_step_object

[Avram]

Hi all,

Can someone look at this code and please let me know what I'm doing incorrectly? What it *should* do is send my NPCs to a randomly chosen instance of a door but I receive the following error:

############################################################################################
ERROR in
action number 1
of Step Event0
for object obj_pedestrian_smart:

Unable to find instance for object index -4
at gml_Object_obj_pedestrian_smart_Step_0 (line 3) - mp_potential_step(inst.x, inst.y, 1, 1);
############################################################################################
gml_Object_obj_pedestrian_smart_Step_0 (line 3)

Here is the code I'm using:

CREATE

door_to_go = instance_find(obj_door_exit, irandom(instance_number(obj_door_exit) - 1));

STEP

inst = door_to_go;

mp_potential_step(inst.x, inst.y, 1, 1);
mp_potential_step_object (inst.x, inst.y, 1, obj_block);

 

[Nocturne]

You are not checking for what happens if the door doesn't exist. The code is assuming it always does, but the error is saying otherwise. Simply wrap the check in a call to instance_exists, eg:

if instance_exists(door_to_go)
{
mp_potential_step_object(door_to_go.x, door_to_go.y, 1, obj_block);
}

Also note that using mp_potential_step() before the object function does nothing. Use one or the other... Also no need for the inst variable.

 

[Avram]

Thank you for the prompt reply! I will try this out later when I’m back on my PC.
Incidentally, I am using this method of pathfinding because I assume the mp_grid/A* method doesn’t allow to send NPCs to different locations simultaneously?

 

[O.Stogden]

Thank you for the prompt reply! I will try this out later when I’m back on my PC.
Incidentally, I am using this method of pathfinding because I assume the mp_grid/A* method doesn’t allow to send NPCs to different locations simultaneously?

The mp_grid functions work hand-in-hand with the path system.

The mp_grid_create just creates a grid which has "valid" places and "invalid" places (usually walls etc.). Each object using the grid (in your case your NPC's) would have a "path" for itself, it can then use the grid to create a valid path between places on the grid, whilst avoiding the walls, using the mp_grid_path function. It's generally much better than mp_potential_* functions, but I imagine it takes more processing power.

 

[Avram]

Thanks, everyone. What's strange is that the NPCs now just stay in one position, so I'm going to try using mp_grid instead.

 

[Avram]

Ugh. I was referring to the wrong object name. Changed it, and it works fine. Thanks again, everyone!