草地编辑器-草的绘制

2023-04-02

草地编辑器

5.7k words

Desc:

草地编辑器之缝合怪

效果

Image text

草的绘制

上一篇中，已经得到了需要绘制的草的信息，包括顶点、法线、顶点色等，其中顶点由一个 Vector3 存储,可以通过CPU计算出，草对应的顶点位置，传递给GPU，也可以通过计算着色器的方式，让GPU去计算草的顶点位置信息

脚本通过 ComputeBuffer 将数据传递给计算着色器

ComputeBuffer

private ComputeBuffer m_sourceVertexBuffer;
private ComputeBuffer m_drawBuffer;
private ComputeBuffer m_argsBuffer;
...


m_sourceVertexBuffer = new ComputeBuffer(vertices.Length, Source_Vert_Stride, ComputeBufferType.Structured, ComputeBufferMode.Immutable);
m_sourceVertexBuffer.SetData(vertices);

m_drawBuffer = new ComputeBuffer(numSourceVertices * maxBladeTriangles, Draw_Stride, ComputeBufferType.Append);
m_drawBuffer.SetCounterValue(0);

m_argsBuffer = new ComputeBuffer(1, Indirect_Args_Stride, ComputeBufferType.IndirectArguments);

m_idGrassKernel = m_instantiatedComputeShader.FindKernel("Main");

m_instantiatedComputeShader.SetBuffer(m_idGrassKernel, "_SourceVertices",m_sourceVertexBuffer);
m_instantiatedComputeShader.SetBuffer(m_idGrassKernel, "_DrawTriangles", m_drawBuffer);
m_instantiatedComputeShader.SetBuffer(m_idGrassKernel, "_IndirectArgsBuffer", m_argsBuffer);


m_instantiatedMaterial.SetBuffer("_DrawTriangles", m_drawBuffer);

更新


// LateUpdate is called after all Update calls
private void LateUpdate(){
    // Clear the draw and indirect args buffers of last frame's data
    m_drawBuffer.SetCounterValue(0);
    m_argsBuffer.SetData(argsBufferReset);



    // Update the shader with frame specific data
    SetGrassDataUpdate();

    // Dispatch the grass shader. It will run on the GPU
    m_instantiatedComputeShader.Dispatch(m_idGrassKernel, m_dispatchSize, 1, 1);

    // DrawProceduralIndirect queues a draw call up for our generated mesh
    Graphics.DrawProceduralIndirect(m_instantiatedMaterial, bounds, MeshTopology.Triangles,
    m_argsBuffer, 0, null, null, castShadow, true, gameObject.layer);

}

ComputeBuffer

缓冲对象（Buffer Object）传递：缓冲对象是一种可以在GPU端存储数据的对象，它可以用来传递一些较大的数据结构，如矩阵、数组等。在Shader中，可以通过glBindBuffer和glVertexAttribPointer函数绑定和传递缓冲对象

在Unity中，缓冲对象（Buffer Object）通常指的是ComputeBuffer。ComputeBuffer是一种可以在GPU端存储数据的对象，它可以用来传递一些较大的数据结构，如矩阵、数组等，以及用于计算着色器的数据。ComputeBuffer可以在Unity中使用ComputeShader进行创建和绑定，可以通过SetBufferData方法和GetData方法来传递数据和获取数据

除了ComputeBuffer，Unity中还有其他类型的缓冲对象，如GraphicsBuffer、VertexBuffer、IndexBuffer等，这些缓冲对象通常用于渲染过程中，用于传递顶点数据、索引数据等。在Unity中，可以通过Mesh类的SetVertexBufferParams和SetIndexBufferParams方法来创建和绑定这些缓冲对象

计算着色器中数据的创建

SourceVertices

struct SourceVertex
{
    float3 positionOS; // position in object space
    float3 normalOS;
    float2 uv;  // contains widthMultiplier, heightMultiplier
    float3 color;
};

上一步中存储的顶点信息，由C#脚本传递给 Compute Shader,cs中根据顶点数据进而创建相关草的顶点信息

DrawTriangle

// This describes a vertex on the generated mesh
struct DrawVertex
{
    float3 positionWS; // The position in world space
    float2 uv;
    float3 color;
};

// A triangle on the generated mesh
struct DrawTriangle
{
    float3 normalOS;
    DrawVertex vertices[3]; // The three points on the triangle
};

计算着色器中返回给Shader的数据结构，代表着一个三角面的数据，包括法线、世界空间坐标、顶点色信息.三角面的三个顶点法线是一致的

Data Create

Image text
来源
每个位置去设置相应的叶片、草数量信息

写入缓存中


AppendStructuredBuffer<DrawTriangle> _DrawTriangles;
...

for (int k = 0; k < numTrianglesPerBlade; ++k)
{
    DrawTriangle tri = (DrawTriangle)0;
    tri.normalOS = faceNormal;
    tri.vertices[0] = drawVertices[k];
    tri.vertices[1] = drawVertices[k + 1];
    tri.vertices[2] = drawVertices[k + 2];
    _DrawTriangles.Append(tri);
}

InterlockedAdd(_IndirectArgsBuffer[0].numVerticesPerInstance,
numTrianglesPerBlade * numBladesPerVertex * 3);

Shader中的计算

数据结构


// This describes a vertex on the generated mesh
struct DrawVertex
{
    float3 positionWS; // The position in world space
    float2 uv;
    float3 diffuseColor;
};

// A triangle on the generated mesh
struct DrawTriangle
{
    float3 normalOS;
    DrawVertex vertices[3]; // The three points on the triangle
};

StructuredBuffer<DrawTriangle> _DrawTriangles;

顶点着色器中数据的读取


// -- retrieve data generated from compute shader
v2f vert(uint vertexID : SV_VertexID)
{
    // Initialize the output struct
    v2f output = (v2f)0;
    DrawTriangle tri = _DrawTriangles[vertexID / 3];
    DrawVertex input = tri.vertices[vertexID % 3];

    output.positionCS = UnityWorldToClipPos(input.positionWS);
    output.positionWS = input.positionWS;

    float3 faceNormal = tri.normalOS;
    output.normalWS = UnityObjectToWorldNormal(faceNormal);
    output.uv = input.uv;

    output.diffuseColor = input.diffuseColor;

    return output;
}

像素着色器部分



void UpdateTex()
{
    camToDrawWith.enabled = true;
    camToDrawWith.targetTexture = tempTex;
    Shader.SetGlobalTexture("_TerrainDiffuse", tempTex);
}
public void DrawDiffuseMap()
{
    DrawToMap("_TerrainDiffuse");
}

void DrawToMap(string target)
{
    camToDrawWith.enabled = true;
    camToDrawWith.targetTexture = tempTex;
    camToDrawWith.depthTextureMode = DepthTextureMode.Depth;
    Shader.SetGlobalFloat("_OrthographicCamSize", camToDrawWith.orthographicSize);
    Shader.SetGlobalVector("_OrthographicCamPos", camToDrawWith.transform.position);
    camToDrawWith.Render();
    Shader.SetGlobalTexture(target, tempTex);
    camToDrawWith.enabled = false;
}

fixed4 frag (v2f i) : SV_Target
{
    ...
    _TopTint = _TopTint * ambient;  
    // tint the top blades and add in light color             
    terrainForBlending = lerp(terrainForBlending,terrainForBlending+ ( _TopTint* float4(i.diffuseColor, 1)) , verticalFade);
    // final = lerp((terrainForBlending)  * shadow , terrainForBlending, shadow);  
    final = terrainForBlending;
    return _MainColor;
}