GetTouchingParts or checking each object if their position is the same?

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#1

So, I’m making a grid-based building system and want to check if the object the player is trying to place is on another object. I got two ways to do this, loop through all the objects in the grid system if they are the same position as the block the player is placing OR get the parts that are touching the block the player is trying to place.

I want to make this as performant as possible since this is running on a while loop.

#2

A common approach in programming is to sacrifice memory for computation speed. If you store some things that you know you’ll need later, you won’t have to compute it every single time. If you choose good algorithms and data structures, you’ll have a much better chance of making something that works and works well.

One data structure that sounds like it might be handy in your case is a “2D table”. I usually implement that like so:

function mapGet(map, x, y)
	if map[x] then
		return map[x][y]
	end
end

function mapSet(map, x, y, value)
	map[x] = map[x] or {}
	map[x][y] = value
end

Creating a new map is as simple as making a new table and just not using it for anything else. E.g.

local gridMap = {}

You can update the gridmap when an object is placed, something like this:

function placeObject(objectPrefab, gridX, gridY)
	local oldObject = mapGet(gridMap, gridX, gridY)
	if oldObject then
		oldObject:Destroy()
	end

	local newObject = objectPrefab:Clone()
        --probably set the object position
	mapSet(gridMap, gridX, gridY, newObject)
	
	return newObject
end

And you can check to see if a grid coordinate is occupied like this:

function isGridCoordOccupied(gridX, gridY)
	return mapGet(gridMap, gridX, gridY) ~= nil
end

There’s some upfront work in updating the grid map. It’s not much when you’re just placing down single objects one at a time, but if you’re e.g. loading in a save game with 100s of placed objects all at once, it might take a second. It’s worth it though because we can check if a grid coordinate is occupied just with two table lookups, no complicated 3D math for collision detection or anything. It’s pretty much instant.

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#4

Thanks for the details about using arrays for checking grid coordinates! I will definitely use this method when my grid map holds a lot of objects.

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#5

I’m glad it’'s useful to you :slight_smile: I’ve used this approach a lot for various projects, so if you have questions or issues with that, feel free to ask here or make another post and message me to let me know :+1:

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