When there are multiple objects of the same type, how do I know which one I am colliding with?

Question

I'm working on a platformer game using Gamemaker Studio 2. , and currently I'm dealing with implementing platforms:

(Platforms are able to pass through from the bottom, but remains solid when landing on)

It's all working good and well for a single platform, but when I add multiple, then only the lowest placed platforms will work properly. I'm already aware that the problem lies on the second if-statement in the code below.

if (place_meeting(x, y+mySpeed[1], o_platform) &&       //If the player collides with a platform
    mySpeed[1] > 0  )                                   //if the player is falling
{
    if ((y + 29) < o_platform.y)                        //if the player's feets are located higher than a platform
    {
        while !place_meeting(x, y+sign(mySpeed[1]), o_platform)
        {
            y += sign(mySpeed[1]);
        }
        mySpeed[@ 1] = 0;
    }
}

The problem is likely because it's reading information from any platform. but not the higher platform I'm colliding with. So I should need a check to make sure I'm talking about the same object I'm colliding with.

If it was a build-in collision event, I could use the other statement to get the right instance, but currently I'm using place_meeting in a step method to collide, and other would be too broad to use properly. So how would I be able to archieve this?

Answer 1

Instance_place did the trick.
If you want to use the object ID outside the collision event, then you can use Instance_Place instead of Place_Meeting.

var myObject = instance_place(x, y, object)
if (myObject != noone)
{
    //...you can use myObject as the object it's colliding with.
}

Answer 2

• Have an array objects (or a dict of )
• Give your objects a ulong ID field
• Whenever you create an object, assign it an ID incrementally and then index it into the array with that id

Now whenever you collide with an object you just called:

var myCollider = arrayOfObjects[object.ID]

NOTE: It'd be better to do this with a Dictionary if you're in C#, but since I don't know what language you're in I gave you a starting point of using an array. An array in this implementation may well waste a lot of memory if you have lots of destructable objects.

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The other way to do this is usually done by a Delegate (or a callback depending on your language.) I would imagine if you're in game-maker that you can probably find something out there on this; but the above will work either way.