乘以顶点数据导致轮廓不均匀（shaderlab unity3d）

Question

我在 Unity3D 的着色器实验室中创建了一个简单的轮廓着色器，其中包含两个通道：一个通道通过沿顶点法线乘以顶点信息来放大对象，两个通道绘制对象的常规（基础通道）版本。问题出在大纲传递的代码中：

Pass {
    Name "OUTLINE"

    ZWrite Off
    Blend SrcAlpha OneMinusSrcAlpha // Normal

    CGPROGRAM
    #pragma vertex vert
    #pragma fragment frag
    #include "UnityCG.cginc"

    struct appdata {
        float4 vertex : POSITION;
        float3 normal : NORMAL;
    };

    struct v2f {
        float4 position : POSITION;
        float3 normal : NORMAL;
    };

    uniform float _OutlineWidth;
    uniform float4 _OutlineColor;

    v2f vert(appdata v) {
        v.vertex.xyz *=  _OutlineWidth;

        v2f o;
        o.position = UnityObjectToClipPos(v.vertex);
        return o;
    }

    half4 frag(v2f i) : COLOR {
        return _OutlineColor;
    }

    ENDCG
}

_OutlineWidth和_OutlineColor分别是Range和Color类型。我已将此着色器应用于几个以编程方式创建的 "tetromino-like" 网格。结果是这样的（点击链接）：

image one image two

如您所见，创建了轮廓，但轮廓沿对象的外边缘 宽度不均匀 。沿着其中一张脸，轮廓更大——沿着离形状中心最远的脸更大。对于非凸形状，问题会被放大；轮廓甚至可能根本不包含形状：

image three

我知道这是因为顶点位置是相对于形状的中心的，而线 v.vertex.xyz *= _OutlineWidth 只是将该位置乘以一个常数（使其远离形状的中心）目的）。如何修改我的代码，使轮廓像素的计算独立于形状的中心并与对象的真实轮廓保持一致？

Answer 1

正如@Gnietschow所说，你需要使用那些顶点的"smooth normals"来知道展开轮廓的方向：

资料来源：FrostSoft

一种方法是在 C# 中计算软法线，然后将它们指定为顶点数据。此示例使用 uv2 和 uv3 通道来保存平滑的法线分量：

Mesh mesh = GetComponent<MeshFilter>().mesh;

Vector3[] meshVertices = mesh.vertices;
//map vertex positions to the ids of all vertices at that position
Dictionary<Vector3, List<int>> vertexMerge = new Dictionary<Vector3, List<int>>();
for(int i = 0; i < mesh.vertexCount; i++) {
    Vector3 vectorPosition = meshVertices[i];

    if(!vertexMerge.ContainsKey(vectorPosition)) {
        //if not already in our collection as a key, add it as a key
        vertexMerge.Add(vectorPosition, new List<int>());
    }

    //add the vertex id to our collection
    vertexMerge[vectorPosition].Add(i);
}

//map vertexIDs to the averaged normal
Vector3[] meshNormals = mesh.normals;
Vector3[] vertexAveragedNormals = new Vector3[mesh.vertexCount];

foreach (List<int> duplicatedVertices in vertexMerge.Values) {
    //calculate average normal
    Vector3 sumOfNormals = Vector3.zero;
    foreach (int vertexIndex in duplicatedVertices) {
        sumOfNormals += meshNormals[vertexIndex];
    }

    Vector3 averagedNormal = (sumOfNormals /= duplicatedVertices.Count).normalized; //average is sum divided by the number of summed elements

    //write the result to our output
    foreach (int vertexIndex in duplicatedVertices) {
        vertexAveragedNormals[vertexIndex] = averagedNormal;
    }
}


//write the result to mesh.
//x and y components shoved into uv3, z component shoved into uv4, with w component of 1.
Vector2[] vertexAveragedNormalsXY = new Vector2[mesh.vertexCount];
Vector2[] vertexAveragedNormalsZW = new Vector2[mesh.vertexCount];
for(int i = 0; i < mesh.vertexCount; i++) {
    Vector3 normal = vertexAveragedNormals[i];
    vertexAveragedNormalsXY[i] = new Vector2(normal.x, normal.y);
    vertexAveragedNormalsZW[i] = new Vector2(normal.z, 1);
}

mesh.uv3 = vertexAveragedNormalsXY;
mesh.uv4 = vertexAveragedNormalsZW;

来源：Reddeyfish-

然后，您使用 TEXCOORD2 和 TEXCOORD3 重建 vert 中的平滑法线。使用它们相应地移动你的顶点位置，同时保持顶点法线与任何照明目的相同的硬法线：

Pass {
    Name "OUTLINE"

    ZWrite Off
    Blend SrcAlpha OneMinusSrcAlpha // Normal

    CGPROGRAM
    #pragma vertex vert
    #pragma fragment frag
    #include "UnityCG.cginc"

    struct appdata {
        float4 vertex : POSITION;
        float3 normal : NORMAL;
        float4 texcoord2 : TEXCOORD2;
        float4 texcoord3 : TEXCOORD3;
    };

    struct v2f {
        float4 position : POSITION;
        float3 normal : NORMAL;
    };

    uniform float _OutlineWidth;
    uniform float4 _OutlineColor;

    v2f vert(appdata v) {
        // add the outline width in the direction of the shared normal
        float3 sharedNormal = float3(v.texcoord2.xy, v.texcoord3.x);

        v.vertex.xyz +=  _OutlineWidth * sharedNormal;  

        v2f o;
        o.position = UnityObjectToClipPos(v.vertex);
        return o;
    }

    half4 frag(v2f i) : COLOR {
        return _OutlineColor;
    }

    ENDCG
}

乘以顶点数据导致轮廓不均匀（shaderlab unity3d）

multiplying vertex data causes uneven outline (shaderlab unity3d)

shader

cg

hlsl

unity3d

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