我在Compute Shader中对GPU上的数组索引有问题，而且我已经坚持了好几个星期。
我正在尝试使用SV_DispatchThreadID的x值作为我的粒子数组的索引（如在Web上的一些示例中所示）。
它正在工作......但是threadID变量（在main函数中）总是返回0,3,6,9,12,15 ...而不是0,1,2,3,4，...
我在CPU端的调度调用是：Dispatch（64,1,1）;
我尝试了许多配置调度（32,16,1），（128,1,1），...有许多配置的numtheards（1,1,1），（32,32,1） ，（16,16,1）...但总是相同的结果...... threadID从来没有很好的排序。
如何获得有序索引？ :( ...总是得到索引，如0,3,6,9，......
有什么建议吗？
非常感谢。
这是我的CS内核和我的C＃源代码：
#pragma kernel CSMain
float dt;
float time;
float pi;
uint maxParticles = 1024;
float maxAge;
struct Particle
{
int index;
float3 position;
float3 velocity;
float size;
float age;
float normAge;
int type;
};
RWStructuredBuffer <Particle> particles;
[numthreads( 1, 1, 1 )]
void CSMain ( uint3 Gid : SV_GroupID, uint3 DTid : SV_DispatchThreadID, uint3 GTid : SV_GroupThreadID, uint GI : SV_GroupIndex )
{
uint index = DTid.x;
if (index < maxParticles)
{
Particle p = particles[index];
p.position.y = p.index; //just check if the index is correct by giving a Y position
particles[index] = p;
}
}
用于创建ComputeBuffer和其他东西的C＃代码：
using UnityEngine;
using System.Collections;
using System.Runtime.InteropServices;
public class SimpleEmitter : MonoBehaviour
{
struct Particle
{
public int index;
public Vector3 position;
public Vector3 velocity;
public float size;
public float age;
public float normAge;
public int type;
}
public ComputeShader computeShader;
public Material material;
public int maxParticles = 1000000;
public float maxAge = 3.0f;
public float particleSize = 0.5f;
private ComputeBuffer particles;
private int particleSizeOf;
void Start ()
{
Particle p = new Particle();
particleSizeOf = Marshal.SizeOf(p);
Particle[] pInitBuffer = new Particle[maxParticles];
for (int i = 0; i < maxParticles; i++)
{
p = new Particle();
p.index = i;
p.type = 0;
p.age = 0;
p.normAge = 0.1f;
p.size = particleSize * 0.5f + Random.value * particleSize;
p.velocity = new Vector3(0, 0, 0);
pInitBuffer[i] = p;
}
particles = new ComputeBuffer(maxParticles, particleSizeOf, ComputeBufferType.Default);
particles.SetData(pInitBuffer);
computeShader.SetBuffer(0, "particles", particles);
}
void Update()
{
computeShader.SetFloat("dt", Time.deltaTime);
computeShader.SetFloat("time", Time.time);
computeShader.SetFloat("pi", Mathf.PI);
computeShader.SetInt("maxParticles", maxParticles);
computeShader.SetFloat("maxAge", maxAge);
computeShader.Dispatch(0, 64, 1, 1);
}
public void OnPostRender()
{
material.SetPass(0);
material.SetFloat("maxAge", maxAge);
material.SetBuffer("particles", particles);
Graphics.DrawProcedural(MeshTopology.Triangles, maxParticles, 0);
}
void OnDisable()
{
particles.Release();
}
}
这里是顶点，几何和像素着色器：
Shader "Custom/SimpleRS"
{
Properties
{
_ParticleTexture ("Diffuse Tex", 2D) = "white" {}
_Ramp1Texture ("G_Ramp1", 2D) = "white" {}
}
SubShader
{
Pass
{
Tags { "Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Transparent" }
Blend OneMinusDstColor One
Cull Off
Lighting Off
ZWrite Off
Fog { Color (0,0,0,0) }
CGPROGRAM
#pragma target 5.0
#pragma vertex VSMAIN
#pragma fragment PSMAIN
#pragma geometry GSMAIN
#include "UnityCG.cginc"
struct Particle
{
int index;
float3 position;
float3 velocity;
float size;
float age;
float normAge;
int type;
};
StructuredBuffer<Particle> particles;
Texture2D _ParticleTexture;
SamplerState sampler_ParticleTexture;
Texture2D _Ramp1Texture;
SamplerState sampler_Ramp1Texture;
float maxAge;
float maxRad;
struct VS_INPUT
{
uint vertexid : SV_VertexID;
};
//--------------------------------------------------------------------------------
struct GS_INPUT
{
float4 position : SV_POSITION;
float size : TEXCOORD0;
float age : TEXCOORD1;
float type : TEXCOORD2;
};
//--------------------------------------------------------------------------------
struct PS_INPUT
{
float4 position : SV_POSITION;
float2 texcoords : TEXCOORD0;
float size : TEXCOORD1;
float age : TEXCOORD2;
float type : TEXCOORD3;
};
//--------------------------------------------------------------------------------
GS_INPUT VSMAIN( in VS_INPUT input )
{
GS_INPUT output;
output.position.xyz = particles[input.vertexid].position;
output.position.w = 1.0;
output.age = particles[input.vertexid].normAge;
output.size = particles[input.vertexid].size;
output.type = particles[input.vertexid].type;
return output;
}
//--------------------------------------------------------------------------------
[maxvertexcount(4)]
void GSMAIN( point GS_INPUT p[1], inout TriangleStream<PS_INPUT> triStream )
{
float4 pos = mul(UNITY_MATRIX_MVP, p[0].position);
float halfS = p[0].size * 0.5f;
float4 offset = mul(UNITY_MATRIX_P, float4(halfS, halfS, 0, 1));
float4 v[4];
v[0] = pos + float4(offset.x, offset.y, 0, 1);
v[1] = pos + float4(offset.x, -offset.y, 0, 1);
v[2] = pos + float4(-offset.x, offset.y, 0, 1);
v[3] = pos + float4(-offset.x, -offset.y, 0, 1);
PS_INPUT pIn;
pIn.position = v[0];
pIn.texcoords = float2(1.0f, 0.0f);
pIn.size = p[0].size;
pIn.age = p[0].age;
pIn.type = p[0].type;
triStream.Append(pIn);
pIn.position = v[1];
pIn.texcoords = float2(1.0f, 1.0f);
triStream.Append(pIn);
pIn.position = v[2];
pIn.texcoords = float2(0.0f, 0.0f);
triStream.Append(pIn);
pIn.position = v[3];
pIn.texcoords = float2(0.0f, 1.0f);
triStream.Append(pIn);
}
//--------------------------------------------------------------------------------
float4 PSMAIN( in PS_INPUT input ) : COLOR
{
float4 color = _ParticleTexture.Sample( sampler_ParticleTexture, input.texcoords );
float4 tint = _Ramp1Texture.Sample(sampler_Ramp1Texture, float2(min(1.0, input.age),0));
color *= tint;
if (input.age == 0) discard;
return color;
}
//--------------------------------------------------------------------------------
ENDCG
}
}
}
答案 0 :(得分：4)
你应该使用MeshTopology.Points而不是三角形绘图。
由于几何着色器只传递了一个点，这就是你的拓扑结构，然后GS根据你的着色器代码将其扩展为三角形。
这解释了为什么只出现每个第三个粒子。它们按照你要求的拓扑结构以3个为一组传递给GS，然后你透明地丢弃第2和第3个输入，GS看到的下一个顶点是Vertex 3，然后是6，然后是9等。