How to draw grass sprites without using gameobjects?

Question

I am making a rimworld-like procedurally generated 2D game using Unity's tilemap system.

Just like tiles, I also have to procedurally generate grass and trees. Each grass instance should have logic inside that keeps track of it's growth progress and update the grass size appropriately.

The downside is, I have to have maps as big as 400x400. That could be THOUSANDS of grass instances and each of them having their own GameObject seems ridiculous and like the game would lag.

How can instantiate those grass sprites without creating new gameobjects for each one while still being able to control the growth and similar things?

(Come to think of it, the DOTS / ECS system in Unity would be perfect for this, however it is nowhere near ready and many things I want to do are just not supported.)

Answer 1

Create a TileMap with 400x400 tiles for your grass tiles. Tiles on a TileMap aren't full-fledged gameObjects. They are very lightweight. A 400x400 tilemap is absolutely no problem.

Then create one gameObject. Let's call it GrassManager and put a script with the same name on it. That script internally has a tile[400][400] array and a reference to that TileMap. Those array entries contain structs with all the data related to the grass growth of each tile. Like whether or not it has grass at all, its current growth progress, any tile properties which influence grass growth (moisture? temperature? fertility?) and when it was last updated.

Then Implement its Update method to go through all those tiles and update their growth status. When that Update-function notices that a grass tile has reached its next growth stage, then you update that tile of the tilemap. Note that you likely do not need to process all the grass tiles on every single update. It is likely completely sufficient for your use-case to do staggered updates where you only process a small chunk of all tiles in each Update-call.