openGL中不正确的被遮挡，正面剔除

Question

我正在使用自己的算法来剔除永远不会显示的被遮挡的正面。当我不剔除脸部时，我有一套完美的积木。当我启用脸部剔除时，我会有意想不到的结果。我检查了我的剔除代码，我相信它正在剔除适当的面孔。

为了简单起见，我将输出减少到了9箱的平面。例如，平面中间的盒子只需要有一个顶面和一个底面。所有其他面孔都可以丢弃，因为它们根本无法在任何地方被人看到。

我检查了代码中的每个方框，以确定他们是否有正确的面孔被淘汰，我相信他们这样做了。这让我觉得我的顶点，索引或法线都有问题。

我正在使用python的Pyglet，它可以自动创建和管理VAO和VBO。

OpenGL设置：

    glEnable(GL_DEPTH_TEST)
    glEnable(GL_CULL_FACE)

OpenGL On Draw：

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)

顶点代码：

        v0 = [1,  1,  1]
        v1 = [-1,  1,  1]
        v2 = [-1, -1,  1]
        v3 = [1, -1,  1]
        v4 = [1, -1, -1]
        v5 = [1,  1, -1]
        v6 = [-1,  1, -1]
        v7 = [-1, -1, -1]
        pt = self.point
        s = getattr(self, 'scale', 0.5)
        faces = ((k, v) for k, v in (
            ('front', [v * s + p for vert in [v0, v1, v2, v3]
                       for v, p in zip(vert, pt)]),
            ('right', [v * s + p for vert in [v0, v3, v4, v5]
                       for v, p in zip(vert, pt)]),
            ('top', [v * s + p for vert in [v0, v5, v6, v1]
                     for v, p in zip(vert, pt)]),
            ('left', [v * s + p for vert in [v1, v6, v7, v2]
                      for v, p in zip(vert, pt)]),
            ('bottom', [v * s + p for vert in [v7, v4, v3, v2]
                        for v, p in zip(vert, pt)]),
            ('back', [v * s + p for vert in [v4, v7, v6, v5]
                      for v, p in zip(vert, pt)]))
            if getattr(self, k)
        )

法线代码：

        verts_per_face = 4
        faces = ((k, v) for k, v in (
            ('front', [0, 0, 1] * verts_per_face),
            ('right', [1, 0, 0] * verts_per_face),
            ('top', [0, 1, 0] * verts_per_face),
            ('left', [-1, 0, 0] * verts_per_face),
            ('bottom', [0, -1, 0] * verts_per_face),
            ('back', [0, 0, -1] * verts_per_face))
            if getattr(self, k)
        )

指数代码：

        t0 = [0,  1,  2]
        t1 = [2,  3,  0]
        t2 = [4,  5,  6]
        t3 = [6,  7,  4]
        t4 = [8,  9, 10]
        t5 = [10, 11,  8]
        t6 = [12, 13, 14]
        t7 = [14, 15, 12]
        t8 = [16, 17, 18]
        t9 = [18, 19, 16]
        t10 = [20, 21, 22]
        t11 = [22, 23, 20]
        triangles = ((k, v) for k, v in (
            ('front', [t for triangle in [t0, t1] for t in triangle]),
            ('right', [t for triangle in [t2, t3] for t in triangle]),
            ('top', [t for triangle in [t4, t5] for t in triangle]),
            ('left', [t for triangle in [t6, t7] for t in triangle]),
            ('bottom', [t for triangle in [t8, t9] for t in triangle]),
            ('back', [t for triangle in [t10, t11] for t in triangle]))
            if getattr(self, k)
        )

剔除代码：

                for face, neighbor_point in block.neighbors():
                    # import pdb; pdb.set_trace()
                    if neighbor_point in pts:
                        neighbor = self.blocks.get(neighbor_point)
                        if neighbor:
                            setattr(block, face, False)
                        else:
                            setattr(block, face, True)
                    else:
                        setattr(block, face, True)

在其中一个方框上剔除前面和左面后的示例输出：

<Voxel (1,0,1)  # top right corner box in images /w center point = (1, 0, 1)
[f r t l o a]   # front, right, top, left, bottom, back
[ |+|+| |+|+]   # + = face available,  ' ' = face culled
(1, 0, 0) (1, 0, 0) (1, 0, 0) (1, 0, 0)  # right normals
(0, 1, 0) (0, 1, 0) (0, 1, 0) (0, 1, 0)  # top normals
(0, -1, 0) (0, -1, 0) (0, -1, 0) (0, -1, 0)  # bottom normals 
(0, 0, -1) (0, 0, -1) (0, 0, -1) (0, 0, -1)  # back normals
[ 1.50| 0.50| 1.50|  # right verts
  1.50|-0.50| 1.50| 
  1.50|-0.50| 0.50| 
  1.50| 0.50| 0.50| 
  1.50| 0.50| 1.50|  # top verts
  1.50| 0.50| 0.50| 
  0.50| 0.50| 0.50| 
  0.50| 0.50| 1.50| 
  0.50|-0.50| 0.50|  # bottom verts
  1.50|-0.50| 0.50| 
  1.50|-0.50| 1.50| 
  0.50|-0.50| 1.50| 
  1.50|-0.50| 0.50|  # back verts
  0.50|-0.50| 0.50| 
  0.50| 0.50| 0.50| 
  1.50| 0.50| 0.50]>

Answer 1

请参阅here了解如何实施剔除算法。在你的剔除代码中，你正在做一些完全无关紧要的事情。要确定是否应该剔除面部，您只需要检查它的缠绕顺序（假设您提供与其法线相关的CW或CCW顺序的所有三角形）。如果您的三角形没有排序，那么为了确定剔除，您必须检查三角形顶点的z顺序，这是图形卡自动执行的操作。如果你决定自己实现它，你将有效地实现软件渲染（尽管渲染为三角形片段，而不是单个像素）。

Answer 2

我没有正确计算指数。新方法应该是：

        t0 = [0,  1,  2]
        t1 = [2,  3,  0]
        t2 = [4,  5,  6]
        t3 = [6,  7,  4]
        t4 = [8,  9, 10]
        t5 = [10, 11,  8]
        t6 = [12, 13, 14]
        t7 = [14, 15, 12]
        t8 = [16, 17, 18]
        t9 = [18, 19, 16]
        t10 = [20, 21, 22]
        t11 = [22, 23, 20]
        triangles = ((k, v) for k, v in (
            ('front', [t for triangle in [t0, t1] for t in triangle]),
            ('right', [t for triangle in [t2, t3] for t in triangle]),
            ('top', [t for triangle in [t4, t5] for t in triangle]),
            ('left', [t for triangle in [t6, t7] for t in triangle]),
            ('bottom', [t for triangle in [t8, t9] for t in triangle]),
            ('back', [t for triangle in [t10, t11] for t in triangle]))
        )
        inds = []
        faces = [f for f, v in self.faces if v]
        for triangle, face in zip(triangles, faces):
            f, tdata = triangle
            inds.extend(tdata)