How to make large 2d tilemap easier to load in Unity

Question

I am creating a small game in the Unity game engine, and the map for the game is generated from a 2d tilemap. The tilemap contains so many tiles, though, is is very hard for a device like a phone to render them all, so the frame rate drops. The map is completely static in that the only moving thing in the game is a main character sprite and the camera following it. The map itself has no moving objects, it is very simple, there must be a way to render only the needed sections of it or perhaps just render the map in once. All I have discovered from researching the topic is that perhaps a good way to do it is buy using the Unity mesh class to turn the tilemap into a mesh. I could not figure out how to do this with a 2d tilemap, and I could not see how it would benefit the render time anyways, but if anyone could point me in the right direction for rendering large 2d tilemaps that would be fantastic. Thanks.

Tile system: To make the tile map work I put every individual tile as a prefab in my prefab folder, with the attributes changed for 2d box colliders and scaled size. I attribute each individual prefab of the tile to a certain color on the RGB scale, and then import a png file that has the corresponding colors of the prefabs where I want them like this:

I then wrote a script which will place each prefab where its associated color is. It would look like this for one tile:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Map : MonoBehaviour {

    private int levelWidth;
    private int levelHeight;

    public Transform block13;

    private Color[] tileColors;

    public Color block13Color;

    public Texture2D levelTexture;

    public PlayerMobility playerMobility;

    // Use this for initialization
    void Start () {
        levelWidth = levelTexture.width;
        levelHeight = levelTexture.height;
        loadLevel ();
    }

    // Update is called once per frame
    void Update () {

    }

    void loadLevel(){
        tileColors = new Color[levelWidth * levelHeight];
        tileColors = levelTexture.GetPixels ();

        for (int y = 0; y < levelHeight; y++) {
            for (int x = 0; x < levelWidth; x++) {
//              if (tileColors [x + y * levelWidth] == block13Color) {
//                  Instantiate(block13, new Vector3(x, y), Quaternion.identity);
//              }
//              
            }
        }
    }
}

This results in a map that looks like this when used with all the code (I took out all the code for the other prefabs to save space)

Answer 1

You can instantiate tiles that are in range of the camera and destroy tiles that are not. There are several ways to do this. But first make sure that what's consuming your resources is in fact the large number of tiles, not something else.

One way is to create an empty parent gameObject to every tile (right click in "Hierarchy" > Create Empty"

then attach a script to this parent. This script has a reference to the camera (tell me if you need help with that) and calculates the distance between it and the camera and instantiates the tile if the distance is less than a value, otherwise destroys the instance (if it's there).

It has to do this in the Update function to check for the distances every frame, or you can use "Coroutines" to do less checks (more efficient).

Another way is to attach a script to the camera that has an array with instances of all tiles and checks on their distances from the camera the same way. You can do this if you only have exactly one large tilemap because it would be hard to re-use this script if you have more than a large tilemap.

Also you can calculate the distance between the tile and the character sprite instead of the camera. Pick whichever is more convenient.

After doing the above and you still get frame-drops you can zoom-in the camera to include less tiles in its range but you'd have to recalculate the distances then.