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Question by dondonbow · Mar 11, 2021 at 11:45 AM · c#shader

Unable to pass array into shader/Trying to create grasses that interacts with multiple objects

Hi, I'm working on a grass shader that will bend the grass on interaction. (to simulate the character trampling the grass) It works fine with single inputs. However, when I try to pass an array of objects into the shader, ONLY the last object on the array list will bend grasses. (For example, on a size 5 array, only the 5th object interacts with the grass in runtime)

Here's the code I attached to the interactor:

 [SerializeField]



 GameObject[] objects;
 Vector4[] positions = new Vector4[100];
 
  void Update()
 {
     for (int i = 0; i < objects.Length; i++)
     {
         positions[i] = objects[i].transform.position;
     }
     Shader.SetGlobalFloat("_PositionArray", objects.Length);
     Shader.SetGlobalVectorArray("_PositionMoving", positions);

 }

The shader code is rather long and here are parts I edited to try to make it take multiple inputs:

 uniform float _PositionArray;
 uniform float3 _PositionMoving[100];

     float3 sphereDisp;
     for (int i = 0; i < _PositionArray; i++) {
         float3 dis = distance(_PositionMoving[i], worldPos); // distance for radius
         float3 radius = 1 - saturate(dis/ _Radius); // in world radius based on objects interaction radius
         sphereDisp = worldPos - _PositionMoving[i]; // position comparison
         sphereDisp *= radius; // position multiplied by radius for falloff
         sphereDisp = clamp(sphereDisp.xyz * _Strength, -0.8, 0.8);
     }

The "sphereDisp" float variable is later used to bend the grass. The For Loop is supposed to pass each object in the array to create a sphereDisp that bends the grass, at least that's how I understand it.

I'm new to Unity, and suspect there also might be something wrong with the "worldPos", but can't tell. The excerpt looks something like this in the script:

 v2g vert(Attributes v)
 {
     float3 v0 = v.positionOS.xyz;

     v2g OUT;
     OUT.pos = v.positionOS;
     OUT.norm = v.normal;
     OUT.uv = v.texcoord;
     OUT.color = v.color;
     return OUT;
 }

 struct g2f
 {
     float4 pos : SV_POSITION;
     float3 norm : NORMAL;
     float2 uv : TEXCOORD0;
     float3 diffuseColor : COLOR;
     float3 worldPos : TEXCOORD3;
     float3 shadows : TEXCOORD4;
     float fogFactor : TEXCOORD5;

 };
 [maxvertexcount(48)]
 void geom(point v2g IN[1], inout TriangleStream<g2f> triStream)
 {float3 worldPos = TransformObjectToWorld(IN[0].pos);

I don't understand the whole "IN[0].pos" thing, whether it will count multiple inputs or just one.

To sum up, my shader only responds to the last object in the array I pass into. I want it to respond to all the objects in the array simultaneously. (Just like in a game, where grasses are trampled by multiple objects such as the player, enemies, npcs...),Hi, I'm working on a grass shader that will bend the grass on interaction. (to simulate the character trampling the grass) It works fine with single inputs. However, when I try to pass an array of objects into the shader, ONLY the last object on the array list will bend grasses. (For example, on a size 5 array, only the 5th object interacts with the grass in runtime)

Here's the code I attached to the interactor:

 [SerializeField]



 GameObject[] objects;
 Vector4[] positions = new Vector4[100];
 
  void Update()
 {
     for (int i = 0; i < objects.Length; i++)
     {
         positions[i] = objects[i].transform.position;
     }
     Shader.SetGlobalFloat("_PositionArray", objects.Length);
     Shader.SetGlobalVectorArray("_PositionMoving", positions);

 }

The shader code is rather long and here are parts I edited to try to make it take multiple inputs:

 uniform float _PositionArray;
 uniform float3 _PositionMoving[100];

     float3 sphereDisp;
     for (int i = 0; i < _PositionArray; i++) {
         float3 dis = distance(_PositionMoving[i], worldPos); // distance for radius
         float3 radius = 1 - saturate(dis/ _Radius); // in world radius based on objects interaction radius
         sphereDisp = worldPos - _PositionMoving[i]; // position comparison
         sphereDisp *= radius; // position multiplied by radius for falloff
         sphereDisp = clamp(sphereDisp.xyz * _Strength, -0.8, 0.8);
     }

The "sphereDisp" float variable is later used to bend the grass. The For Loop is supposed to pass each object in the array to create a sphereDisp that bends the grass, at least that's how I understand it.

I'm new to Unity, and suspect there also might be something wrong with the "worldPos", but can't tell. The excerpt looks something like this in the script:

 v2g vert(Attributes v)
 {
     float3 v0 = v.positionOS.xyz;

     v2g OUT;
     OUT.pos = v.positionOS;
     OUT.norm = v.normal;
     OUT.uv = v.texcoord;
     OUT.color = v.color;
     return OUT;
 }

 struct g2f
 {
     float4 pos : SV_POSITION;
     float3 norm : NORMAL;
     float2 uv : TEXCOORD0;
     float3 diffuseColor : COLOR;
     float3 worldPos : TEXCOORD3;
     float3 shadows : TEXCOORD4;
     float fogFactor : TEXCOORD5;

 };
 [maxvertexcount(48)]
 void geom(point v2g IN[1], inout TriangleStream<g2f> triStream)
 {float3 worldPos = TransformObjectToWorld(IN[0].pos);

I don't understand the whole "IN[0].pos" thing, whether it will count multiple inputs or just one.

To sum up, my shader only responds to the last object in the array I pass into. I want it to respond to all the objects in the array simultaneously. (Just like in a game, where grasses are trampled by multiple objects such as the player, enemies, npcs...)

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