c# - 在 Unity C# 中修复挤压网格法线？

Question

在 Unity C# 中，我正在使用基于平面多边形的 2D 矢量点的程序网格挤压。使用下面的代码效果很好，除了一个细节:似乎每隔一个连接挤压网格正面和背面的三角形都被翻转，如图所示(使用双面着色器，我可以看到所有三角形都这样做存在良好，虽然)。我将如何修复这些桥接法线的翻转？谢谢!

// Extrusion functionality via
// https://forum.unity.com/threads/trying-extrude-a-2d-polygon-to-create-a-mesh.102629/
// with Triangulator based on
// http://wiki.unity3d.com/index.php?title=Triangulator

public static Mesh GetExtrudedMeshFromPoints(Vector2[] points, float depth)
{
    const float frontVertex = 0f;

    Triangulator triangulator = new Triangulator(points);
    int[] tris = triangulator.Triangulate();

    Mesh m = new Mesh();
    Vector3[] vertices = new Vector3[points.Length*2];

    for (int i = 0; i < points.Length; i++)
    {
        vertices[i].x = points[i].x;
        vertices[i].y = points[i].y;
        vertices[i].z = frontVertex;
        vertices[i+points.Length].x = points[i].x;
        vertices[i+points.Length].y = points[i].y;
        vertices[i+points.Length].z = depth;
    }

    int[] triangles = new int[tris.Length*2+points.Length*6];
    int count_tris = 0;

    // Front vertices
    for (int i = 0; i < tris.Length; i += 3)
    {
        triangles[i]   = tris[i];
        triangles[i+1] = tris[i+1];
        triangles[i+2] = tris[i+2];
    } 

    count_tris += tris.Length;
    // Back vertices
    for (int i = 0; i < tris.Length; i += 3)
    {
        triangles[count_tris+i]   = tris[i+2] + points.Length;
        triangles[count_tris+i+1] = tris[i+1] + points.Length;
        triangles[count_tris+i+2] = tris[i]   + points.Length;
    }

    count_tris += tris.Length;
    // Triangles around the perimeter of the object
    for (int i = 0; i < points.Length; i++)
    {
        int n = (i+1) % points.Length;
        triangles[count_tris]   = i;
        triangles[count_tris+1] = i + points.Length;
        triangles[count_tris+2] = n;
        triangles[count_tris+3] = n;
        triangles[count_tris+4] = n + points.Length;
        triangles[count_tris+5] = i + points.Length;
        count_tris += 6;
    }

    m.vertices = vertices;
    m.triangles = triangles;

    m.RecalculateNormals();
    m.RecalculateBounds();
    m.Optimize();

    return m;
}

Answer 1

如果一张脸没有显示出来，就像您已经注意到的那样翻转了，这是由于统一的顺时针方向的缠绕顺序。您的 triangluator 链接已在故障排除下说明: “如果您看不到使用此实用程序创建的多边形，请记住检查多边形是否面向相反的方向。如果是，您可以通过以相反的顺序使用顶点索引构建网格来更改它。”

编辑:

进一步说明:在您的代码中，这意味着您必须切换

// Triangles around the perimeter of the object
        for (int i = 0; i < points.Length; i++)
        {
            int n = (i + 1) % points.Length;
            triangles[count_tris] = i;
            triangles[count_tris + 1] = i + points.Length;
            triangles[count_tris + 2] = n;
            triangles[count_tris + 3] = n;
            triangles[count_tris + 4] = n + points.Length;
            triangles[count_tris + 5] = i + points.Length;
            count_tris += 6;
        }

到

// Triangles around the perimeter of the object
        for (int i = 0; i < points.Length; i++)
        {
            int n = (i + 1) % points.Length;
            triangles[count_tris] = n;
            triangles[count_tris + 1] = i + points.Length;
            triangles[count_tris + 2] = i;
            triangles[count_tris + 3] = n;
            triangles[count_tris + 4] = n + points.Length;
            triangles[count_tris + 5] = i + points.Length;
            count_tris += 6;
        }

但要小心，因为顺序取决于你的深度(如果它高于或低于你的 frontVertex)

第二次编辑:

三角形的法线取决于缠绕顺序，这意味着顺序存在差异。

一个例子:

1: Vector2(1f, 1f);
2: Vector2(1f, 0f);
3: Vector2(0f, 0f);

三角形

Triangle 1,2,3

和

Triangle 1,3,2

有不同的法线。

您必须确保绘制的每个三角形的缠绕顺序一致。 或者你可以告诉你的着色器禁用 culling (使用 Cull Off)，正如您在上面所说的。但这伴随着计算时间的成本。在大多数情况下，这并不重要，但这始终取决于您的目的。此外，大多数时候您不希望出现禁用剔除的副作用。