c++ - 如何为圆环创建索引

Question

我正在将旧的固定功能管道代码移植到着色器，对于环面几何体，我无法创建正确的索引。
旧代码

int CTorus::initevVertex2Ds()
{

    const float twopi = 2.0 * M_PI;

    // factor for texture coordinate per step in X/Y
    const float fXtex = 1. / float(m_nCorners);
    const float fYtex = 1. / float(m_nTesselation);

    int i;

    // go around cross section
    for (i = 0; i < m_nTesselation; i++) {
        register int base = i * m_nCorners;
        register int baseTX = i * (m_nCorners+1);

        // Y texture coordinate ...
        m_texcoord[baseTX].x = fYtex * float(i);

        // go around top view
        const float f2Pi_i_corners = (twopi * float(i+m_nTesselation/2)) / float(m_nTesselation);
        const float evVertex2D_z = m_fRadiusCrossSect * fsin(f2Pi_i_corners);
        const float fXY = m_fRadiusTorus + m_fRadiusCrossSect * fcos(f2Pi_i_corners);

        for (int j = 0; j < m_nCorners; j++) {
            register int index = base + j;

            const float fXj = fcos(twopi*float(j)/m_nCorners);
            const float fYj = fsin(twopi*float(j)/m_nCorners);

            m_GLVertex2D[index].x = fXY * fXj;  
            m_GLVertex2D[index].y = fXY * fYj;   
            m_GLVertex2D[index].z = evVertex2D_z;

            m_texcoord[baseTX + j].y = 1. - fXtex * float(j);
            m_texcoord[baseTX + j].x = m_texcoord[baseTX].x;

            const float nx =  m_GLVertex2D[index].x - m_fRadiusTorus * fXj;
            const float ny =  m_GLVertex2D[index].y - m_fRadiusTorus * fYj;
            const float nz =  m_GLVertex2D[index].z;

            const float n = fsqrt(nx*nx + ny*ny + nz*nz);

            m_norm[index].x = nx/n;
            m_norm[index].y = ny/n;
            m_norm[index].z = nz/n;
        }
        m_texcoord[baseTX + m_nCorners].y = 0.; 
        m_texcoord[baseTX + m_nCorners].x = m_texcoord[baseTX].x;
    }

    for (i=0; i<=m_nCorners; i++) {
        m_texcoord[(m_nCorners+1)*m_nTesselation+i].y = m_texcoord[i].y;
        m_texcoord[(m_nCorners+1)*m_nTesselation+i].x = 1.;
    }
    return 0;
}

这是我已将其移植到着色器的代码，但我无法为元素数组缓冲区正确创建索引

void Torus::init()
{
    const float twopi = 2.0 * M_PI;

    // factor for texture coordinate per step in x/y
    const float fXtex = 1.0 / float(m_nCorners);
    const float fYtex = 1.0 / float(m_nTesselation);

    int i;
    for (i = 0; i < m_nTesselation; i++)
    {
        register int base = i * m_nCorners;
        register int baseTX = i * (m_nCorners + 1);

        // go around top view
        const float f2Pi_i_corners = (twopi * float(i + m_nTesselation / 2)) / float(m_nTesselation);
        const float evVertex2D_z = m_fRadiusCrossSect * sinf(f2Pi_i_corners);
        const float fXY = m_fRadiusTorus + m_fRadiusCrossSect * cosf(f2Pi_i_corners);
        for (int j = 0; j < m_nCorners; j++)
        {
            register int index = base + j;
            
            const float fXj = cosf(twopi*float(j) / m_nCorners);
            const float fYj = sinf(twopi*float(j) / m_nCorners);
            
            data.push_back(fXY * fXj);
            data.push_back(fXY * fYj);
            data.push_back(evVertex2D_z);

            const float nx = (fXY * fXj) - m_fRadiusTorus * fXj;
            const float ny = (fXY * fYj) - m_fRadiusTorus * fYj;
            const float nz = evVertex2D_z;
            const float n = sqrt(nx*nx + ny * ny + nz * nz);
            data.push_back(nx / n);
            data.push_back(ny / n);
            data.push_back(nz / n);
            // Pushing texture coordinates
            data.push_back(0.0);
            data.push_back(0.0);
        }
    }
    std::vector<unsigned int> stdvecIndex;
    unsigned int index;
    // Create the indexes
    for (int i = 0; i < m_nTesselation; i++)
    {
        index = ((i + 1) % m_nTesselation) * m_nCorners;
        stdvecIndex.push_back(index);
        for (int j = 0; j < m_nCorners; j++)
        {
            index = i * m_nCorners + j;
            stdvecIndex.push_back(index);
            index = ((i + 1) % m_nTesselation) * m_nCorners + ((j + 1) % m_nCorners);
            stdvecIndex.push_back(index);
        }
        index = i * m_nCorners;
        stdvecIndex.push_back(index);
    }
    if (!isInited)
    {
        glGenVertexArrays(1, &VAO);
        glGenBuffers(1, &VBO);
        glGenVertexArrays(1, &EBO);
        glBindVertexArray(VAO);
        glBindBuffer(GL_ARRAY_BUFFER, VBO);
        glBufferData(GL_ARRAY_BUFFER, data.size() * sizeof(float), &data[0], GL_STATIC_DRAW);
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
        glBufferData(GL_ELEMENT_ARRAY_BUFFER, stdvecIndex.size() * sizeof(unsigned int), &stdvecIndex[0], GL_STATIC_DRAW);
        glEnableVertexAttribArray(0);
        glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
        glEnableVertexAttribArray(1);
        glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)( 3 * sizeof(float)));
        glEnableVertexAttribArray(2);
        glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(float), (void*)(6 * sizeof(float)));
    }
}

我曾尝试为缓冲区创建索引，但不幸的是，我得到了相互纠缠的几何体，而不是圆环。

Answer 1

glVertexAttribPointer 的跨度(第5个)参数是错误的。 stride指定连续的通用顶点属性之间的字节偏移量。
属性的大小为8(x，y，z，nx，ny，nz，u，v)。
因此，步幅必须为8 * sizeof(float)而不是3 * sizeof(float):

glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
glEnableVertexAttribArray(1);
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(3 * sizeof(float)));
glEnableVertexAttribArray(2);
glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(6 * sizeof(float)));