metaverse_artist/Lux URP Essentials/Lux SRP Grass Displacement/Scripts/ControlDisplacerParticleSys.cs

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

namespace Lux_SRP_GrassDisplacement {

  [RequireComponent(typeof(ParticleSystem))]
  public class ControlDisplacerParticleSys : MonoBehaviour
  {
      
  	public float maxDistance = 1.0f;
    	public float fallOff = 2.0f;
    	
      [Layer]
      public int layerMask = 0;

    	[Space(5)]
      public bool DebugRay = true;

    	private Transform trans;
    	private ParticleSystem ps;
    	private ParticleSystem.MainModule main;

    	private RaycastHit hit;
    	private float alpha;
    	
    	private float min_alpha;
    	private float max_alpha;
    	private Color min_StartColor;
    	private Color max_StartColor;


      void OnEnable() {
      	trans = GetComponent<Transform>();
          ps = GetComponent<ParticleSystem>();
          main = ps.main;
  		    min_StartColor = main.startColor.colorMin;
          min_alpha = min_StartColor.a;
          max_StartColor = main.startColor.colorMax;
          max_alpha = max_StartColor.a;
      }

      void Update() {
  		var mask = 1 << layerMask;
  		if (Physics.Raycast(trans.position, Vector3.down, out hit, maxDistance, mask )) {
  			#if UNITY_EDITOR
  				if(DebugRay) {
  				    Debug.DrawRay(transform.position, Vector3.down * hit.distance, Color.green);
  				}
  			#endif  
  			alpha = (float)(1.0 - Math.Pow(hit.distance / maxDistance, fallOff));
  			min_StartColor.a = min_alpha * alpha;
  			max_StartColor.a = max_alpha * alpha;
  			main.startColor = new ParticleSystem.MinMaxGradient(min_StartColor, max_StartColor);	
  		}
  		else {
  			#if UNITY_EDITOR
  	            if(DebugRay) {
  	                Debug.DrawRay(transform.position, Vector3.down * maxDistance, Color.red);
  	            }
  			#endif
              if (alpha != 0.0f) {
                  alpha = 0.0f;
                  min_StartColor.a = alpha;
  				max_StartColor.a = alpha;
  				main.startColor = new ParticleSystem.MinMaxGradient(min_StartColor, max_StartColor);
              }
          }
      }
  }

}