Pass a object position to shader and calculate the distance

Hi
I just read an article about how to make grass, now I want to step forward, let other objects affect the grass.
Here is the original article https://roystan.net/articles/grass-shader.html

And here is my C# code to pass positions to the shader.

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class MoveInterActive : MonoBehaviour
6. {
7.     // Start is called before the first frame update
8.     public GameObject grassModel;
9.     public Material grassMat;
10.     public Transform[] obstacles;
11.  
12.     private Vector4[] obstaclePositions = new Vector4[100];
13.     private MeshFilter meshFilter;
14.     private MeshRenderer meshRenderer;
15.     void Start()
16.     {
17.         meshFilter = gameObject.AddComponent<MeshFilter> () as MeshFilter;
18.         meshRenderer = gameObject.AddComponent<MeshRenderer> () as MeshRenderer;
19.         meshRenderer.material = grassMat;
20.  
21.     }
22.  
23.     // Update is called once per frame
24.     void Update()
25.     {
26.     for (int n = 0; n < obstacles.Length; n++) {
27.             obstaclePositions [n] = obstacles [n].position;
28.             Debug.Log(obstacles [n].position);
29.         }
30.  
31.     Shader.SetGlobalFloat("_PositionArray", obstacles.Length);
32.     Shader.SetGlobalVectorArray("_ObstaclePositions", obstaclePositions);
33.     //Debug.Log(obstaclePositions [0]);
34.  
35.     }
36.    
37.  
38. }
39.  

And the debug tells me, I go the positions correctly at c# Part.

But when I try to get the distance through this:

Code (CSharp):

1. float4 wodpos = mul(unity_ObjectToWorld, pos);
2. for (int n = 0; n < _PositionArray; n++){
3.              float dis =  distance(wodpos,_ObstaclePositions[n]);
4. (dis<0)?(height=0):(height=1);
5.             };
6. ....
7. triStream.Append(GenerateGrassVertex(pos, segmentWidth, segmentHeight,segmentForward, float2(0, t), transformationMatrixFacing));
8. triStream.Append(GenerateGrassVertex(pos, -segmentWidth, segmentHeight, segmentForward,float2(1, t), transformationMatrixFacing));
9. triStream.Append(GenerateGrassVertex(pos, 0, height,forward, float2(0.5, 1), transformationMatrix));
10.  
11.  

I assume that I need to convert the vertex pos to world cord, but I am not sure. Did I miss anything?

 

UPDATE
i pass the dis to color, and I found it works. So the problem probably is

Code (CSharp):

1. dis = dis - _EffectRadius;
2. dis>0?(height= (rand(pos.zyx) * 2 - 1) * _BladeHeightRandom + _BladeHeight):(height=0);

always goes to the false condition value? Did anybody know why?

 

Is this because I work with geometry shader?

 

I got this， problem solved