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Pass a object position to shader and calculate the distance

Discussion in 'Shaders' started by Isaac_1993, Jun 3, 2020.

  1. Isaac_1993

    Isaac_1993

    Joined:
    May 1, 2020
    Posts:
    7
    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?
     
    Last edited: Jun 3, 2020
  2. Isaac_1993

    Isaac_1993

    Joined:
    May 1, 2020
    Posts:
    7
    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?
     

    Attached Files:

  3. Isaac_1993

    Isaac_1993

    Joined:
    May 1, 2020
    Posts:
    7
    Is this because I work with geometry shader?
     
  4. Isaac_1993

    Isaac_1993

    Joined:
    May 1, 2020
    Posts:
    7
    I got this, problem solved
     
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