GameMaker random spawning without overlap

zim32 · May 24, 2018

I am having trouble keeping my randomly spawned objects from overlapping I tried to have it check for collison with other instances using if object at and having it change x coordinate until it gets one that won't collide but i doesn't seem to work nothing spawns anymore my noob attempt looks like this
num_objects = 8

repeat ( num_objects){

var _x = irandom(room_width)
var _y = 700
var l3654631B_0 = instance_place(obj_spikes.x, obj_spikes.y, obj_spikes);
if ((l3654631B_0 > 0))
{
while ((l3654631B_0 > 0)) {
var _x = irandom(room_width)
var _y = 700 // code here
}

instance_create_layer(_x, _y, "Instances",obj_spikes) // replace "my_object_here" with the real name of your object.
}
}

2Dcube · May 24, 2018

This while loop:

Code:

while ((l3654631B_0 > 0)) {
var _x = irandom(room_width)
var _y = 700 // code here
}

will loop forever once it starts, because l3654631B_0 is never changed. So if it is bigger than 0, it never becomes 0 or less, and the loop continues....forever....and ever...

While loop pseudo code:

Code:

while (this expression is true)
{
   keep_doing_this_code()
}

Also why do you name a variable l3654631B_0 ? Seems difficult to type...

zim32 · May 24, 2018

2Dcube said:
This while loop:

Code:

while ((l3654631B_0 > 0)) { var _x = irandom(room_width) var _y = 700 // code here }

will loop forever once it starts, because l3654631B_0 is never changed. So if it is bigger than 0, it never becomes 0 or less, and the loop continues....forever....and ever...

While loop pseudo code:

Code:

while (this expression is true) { keep_doing_this_code() }

Also why do you name a variable l3654631B_0 ? Seems difficult to type...

i just dragged and dropped the if object at then converted to gml and cut and pasted since the if ((l3654631B_0 > 0)) came from that i thought that meant since it was supposed to be checking if the instances were colliding with each other that
]while ((l3654631B_0 > 0)) {
var _x = irandom(room_width)
var _y = 700 // code here
}[/code]
would change the x variable until it didn't collide with the other instances

Michael McMullen · May 24, 2018

Well you want to basically just check to ensure that you are not overlapping another object of whatever type you don't want to overlap (you could check for free space as well)... anyway I would suggest based on the previous messages it is something like

Code:

// create event
randomize();

var object_count = 10;
var yy = 700; // this is here because we won't change it

repeat(object_count) {
  var xx = random(room_width); // between 0 - room_width
  var times = 3;

  while(place_meeting(xx, yy, obj_obj_spikes) {
    // while there are spikes at our current location, try again
    xx = random(room_width);
    times -= 1; // ensure there is a way out of the loop

    if(times <= 0) {
      break; // we couldn't find an opening, so break out of while loop keeping the xx position
    }
  }

  instance_create_layer(xx, yy, "Instances", obj_spikes);

}

Please note I didn't try this out, just what comes to my mind and there could probably be some syntax errors.

zim32 · May 24, 2018

Michael McMullen said:
Well you want to basically just check to ensure that you are not overlapping another object of whatever type you don't want to overlap (you could check for free space as well)... anyway I would suggest based on the previous messages it is something like

Code:

// create event randomize(); var object_count = 10; var yy = 700; // this is here because we won't change it repeat(object_count) { var xx = random(room_width); // between 0 - room_width var times = 3; while(place_meeting(xx, yy, obj_obj_spikes) { // while there are spikes at our current location, try again xx = random(room_width); times -= 1; // ensure there is a way out of the loop if(times <= 0) { break; // we couldn't find an opening, so break out of while loop keeping the xx position } } instance_create_layer(xx, yy, "Instances", obj_spikes); }

Please note I didn't try this out, just what comes to my mind and there could probably be some syntax errors.

yeah there was a syntax error forgot a ) but fixing the syntax error didn't get it work for me also why is is it obj_obj

zim32 · May 24, 2018

okay i seem to have sort of got it working there's still overlap but never as much as before
i did this
randomize()

var object_count = 6
var yy = 700

repeat(object_count) {
var xx = random(room_width);
while (position_meeting(xx, yy, obj_spikes)) {
xx = random(room_width)
}
instance_create_layer(xx, yy, "Instances", obj_spikes)
}
anyone know how to improve it

Jdown79 · May 25, 2018

could you not patch this by just running a check for collision after spawn?

obj_spikes
step
if place_meeting(with obj_spikes) instance_destroy()
This would remove both, but if your spawn loop works properly and quickly you'd never know

IDK I'm a novice as well haha.

Michael McMullen · May 25, 2018

well position_meeting works based on the collision mask, so if your mask isn't going all the way, that could explain why you have overlap still. So you can either use that, or expand it into something with point_in_rectangle

zim32 · May 25, 2018

Michael McMullen said:
well position_meeting works based on the collision mask, so if your mask isn't going all the way, that could explain why you have overlap still. So you can either use that, or expand it into something with point_in_rectangle

okay making the collsion mask bigger does seem to help but i am having to make the mask way to big for the results i am getting it doesn't make sense it seems to be allowing a certain amount of overlap between collison mask

2Dcube · May 25, 2018

Replace position_meeting() with place_meeting() → https://docs.yoyogames.com/source/d... and collisions/collisions/place_meeting.html
I think position_meeting only check for a point, so not really an overlap. place_meeting check for an overlap (see the image that explains this in the above link).
The math equivalent function would be rectangle_in_rectangle().

zim32 · May 25, 2018

2Dcube said:
Replace position_meeting() with place_meeting() → https://docs.yoyogames.com/source/dadiospice/002_reference/movement and collisions/collisions/place_meeting.html
I think position_meeting only check for a point, so not really an overlap. place_meeting check for an overlap (see the image that explains this in the above link).
The math equivalent function would be rectangle_in_rectangle().

place_meeting doesn't work for me for some reason

Michael McMullen · May 25, 2018

Alright my last attempt

So basically I created a spike, and a generator. Then in the generator I am using collision_rectangle to see if there are any obj_Spike's within the given rectangle. If there is, then it tries again, for a maximum of 10 tries. Finally in the end, if it was indeed an empty space, then it will place a spike at that location, if it does not, then it skips it (failed 10 times).

Code:

// create event of generator

randomize();

var sprite_padding = 10; // two pixels left and right
var spr_width = 32 + sprite_padding; // numbers came from sprite itself
var spr_height = 16;
var yy = 448;

var number_of_spikes = 20;

var tries = 5;
var instance = noone;
var xx = 0;

repeat(number_of_spikes) {
    xx = random(room_width);
    instance = collision_rectangle(xx - spr_width, yy - spr_height, xx + spr_height, yy + spr_width, obj_Spike, false, true)
    tries = 10;
 
    while(instance != noone) {
        show_debug_message("Found spike inside box, trying again: " + string(tries));
     
        // try again
        xx = random(room_width);
     
        // update collision
        instance = collision_rectangle(xx - spr_width, yy - spr_height, xx + spr_height, yy + spr_width, obj_Spike, false, true)
     
        // remove a try
        tries -= 1;
     
        if(tries < 0) {
            // we tried a lot, but break out
            break;
        }
    }
 
    // did we find an empty space?
    if(instance == noone) {
        instance_create_layer(xx, yy, "Instances", obj_Spike);
    }
}

Image Preview

zim32 · May 25, 2018

Michael McMullen said:

Alright my last attempt

So basically I created a spike, and a generator. Then in the generator I am using collision_rectangle to see if there are any obj_Spike's within the given rectangle. If there is, then it tries again, for a maximum of 10 tries. Finally in the end, if it was indeed an empty space, then it will place a spike at that location, if it does not, then it skips it (failed 10 times).

Code:

// create event of generator

randomize();

var sprite_padding = 10; // two pixels left and right
var spr_width = 32 + sprite_padding; // numbers came from sprite itself
var spr_height = 16;
var yy = 448;

var number_of_spikes = 20;

var tries = 5;
var instance = noone;
var xx = 0;

repeat(number_of_spikes) {
    xx = random(room_width);
    instance = collision_rectangle(xx - spr_width, yy - spr_height, xx + spr_height, yy + spr_width, obj_Spike, false, true)
    tries = 10;
 
    while(instance != noone) {
        show_debug_message("Found spike inside box, trying again: " + string(tries));
    
        // try again
        xx = random(room_width);
    
        // update collision
        instance = collision_rectangle(xx - spr_width, yy - spr_height, xx + spr_height, yy + spr_width, obj_Spike, false, true)
    
        // remove a try
        tries -= 1;
    
        if(tries < 0) {
            // we tried a lot, but break out
            break;
        }
    }
 
    // did we find an empty space?
    if(instance == noone) {
        instance_create_layer(xx, yy, "Instances", obj_Spike);
    }
}

Image Preview

thanks so much it seems to work but i had to shrink my sprite to get it to no overlap which i was going to do eventually anway but i wonder if that's all i had needed to do for a while now

GameMaker random spawning without overlap

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