Aetheria/Assets/Plugins/Celestial Body/Scripts/LODHandler.cs

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

[ExecuteInEditMode]
public class LODHandler : MonoBehaviour {
	[Header ("LOD screen heights")]
	// LOD level is determined by body's screen height (1 = taking up entire screen, 0 = teeny weeny speck) 
	public float lod1Threshold = .5f;
	public float lod2Threshold = .2f;

	// [Header ("Debug")]
	// public bool debug;
	// public CelestialBody debugBody;

	Camera cam;
	Transform camT;
	// CelestialBody[] bodies;
	CelestialBodyGenerator[] generators;

	public void FindPlanets()
	{
		generators = FindObjectsOfType<CelestialBodyGenerator> ();
	}

	void Update () {
		//DebugLODInfo ();

		if (Application.isPlaying) {
			HandleLODs ();
		}

	}

	void HandleLODs () {
		for (int i = 0; i < generators.Length; i++) {
			float screenHeight = CalculateScreenHeight (generators[i]);
			int lodIndex = CalculateLODIndex (screenHeight);
			generators[i].SetLOD (lodIndex);

		}
	}

	int CalculateLODIndex (float screenHeight) {
		if (screenHeight > lod1Threshold) {
			return 0;
		} else if (screenHeight > lod2Threshold) {
			return 1;
		}
		return 2;
	}

	// void DebugLODInfo () {
	// 	if (debugBody && debug) {
	// 		float h = CalculateScreenHeight (debugBody);
	// 		int index = CalculateLODIndex (h);
	// 		Debug.Log ($"Screen height of {debugBody.name}: {h} (lod = {index})");
	// 	}
	// }

	float CalculateScreenHeight (CelestialBodyGenerator body) {
		if (cam == null) {
			cam = Camera.main;
			camT = cam.transform;
		}
		Quaternion originalRot = camT.rotation;
		Vector3 bodyCentre = body.transform.position;
		camT.LookAt (bodyCentre);

		var radius = body.transform.localScale.x;
		Vector3 viewA = cam.WorldToViewportPoint (bodyCentre - camT.up * radius);
		Vector3 viewB = cam.WorldToViewportPoint (bodyCentre + camT.up * radius);
		float screenHeight = Mathf.Abs (viewA.y - viewB.y);
		camT.rotation = originalRot;

		return screenHeight;
	}
}