OpenGL复制顶点缓冲区对象

Question

我试图通过复制赋值运算符将两个顶点缓冲区对象从一个Mesh 对象复制到另一个对象。最初，我的顶点数组对象和缓冲区初始化如下：

void Mesh::construct(Vertex* vertices, unsigned int nVerts) {

    vertexCount = nVerts;

    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);

    std::vector<glm::vec3> positions;
    std::vector<glm::vec2> texCoords;

    positions.reserve(nVerts);
    texCoords.reserve(nVerts);

    for (unsigned int i = 0; i < nVerts; i++) {
        positions.push_back(vertices[i].getPosition());
        texCoords.push_back(vertices[i].getTexCoord());
    }

    for (int i = 0; i < NUM_BUFFERS; i++) {
        glGenBuffers(1, &vab[i]);
    }

    glBindBuffer(GL_ARRAY_BUFFER, vab[POSITION_VB]);
    glBufferData(GL_ARRAY_BUFFER, nVerts * sizeof (positions[0]), &positions[0], GL_STATIC_DRAW);

    glBindBuffer(GL_ARRAY_BUFFER, vab[TEXCOORD_VB]);
    glBufferData(GL_ARRAY_BUFFER, nVerts * sizeof (texCoords[0]), &texCoords[0], GL_STATIC_DRAW);

    glEnableVertexAttribArray(1);
    glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, 0);

    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);

    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindVertexArray(0);

}

这在实例化 Mesh 对象并调用时可以正常工作：

void Mesh::render() {

    glBindVertexArray(vao);

    glDrawArrays(GL_TRIANGLES, 0, vertexCount);

    glBindVertexArray(0);

}

但是，当我尝试将网格复制到另一个网格中并进行渲染时，glDrawArrays(GL_TRIANGLES, 0, vertexCount); 行出现分段错误。这是我的复制赋值运算符：

Mesh& Mesh::operator=(const Mesh& param) {

    if (this == &param) {
        return *this;
    } else {

        GLint size = 0;

        glGenVertexArrays(1, &vao);
        glBindVertexArray(vao);

        for (int i = 0; i < NUM_BUFFERS; i++) {
            glGenBuffers(1, &vab[i]);
        }

        // Vertices
        // Bind Buffers
        glBindBuffer(GL_COPY_READ_BUFFER, param.vab[POSITION_VB]);
        glGetBufferParameteriv(GL_COPY_READ_BUFFER, GL_BUFFER_SIZE, &size);

        glBindBuffer(GL_COPY_WRITE_BUFFER, vab[POSITION_VB]);
        glBufferData(GL_COPY_WRITE_BUFFER, size, nullptr, GL_STATIC_DRAW);

        glEnableVertexAttribArray(0);
        glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);

        // Copy Data
        glCopyBufferSubData(GL_COPY_READ_BUFFER, GL_COPY_WRITE_BUFFER, 0, 0, size);

        // Texture Coords
        // Bind Buffers
        glBindBuffer(GL_COPY_READ_BUFFER, param.vab[TEXCOORD_VB]);
        glGetBufferParameteriv(GL_COPY_READ_BUFFER, GL_BUFFER_SIZE, &size);

        glBindBuffer(GL_COPY_WRITE_BUFFER, vab[TEXCOORD_VB]);
        glBufferData(GL_COPY_WRITE_BUFFER, size, nullptr, GL_STATIC_DRAW);

        glEnableVertexAttribArray(1);
        glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, 0);

        // Copy Data
        glCopyBufferSubData(GL_COPY_READ_BUFFER, GL_COPY_WRITE_BUFFER, 0, 0, size);

        // Unbind buffers
        glBindVertexArray(0);

        this->vertexCount = param.vertexCount;

        return *this;
    }

}

有人能看出这有什么问题吗？我检查了从glGetBufferParameteriv(GL_COPY_READ_BUFFER, GL_BUFFER_SIZE, &size); 返回的大小在两种情况下都是正确的（对于位置和纹理坐标缓冲区）。在两次调用glCopyBufferSubData 之后，我还检查了glGetError()，它们都返回0。不确定接下来要尝试什么？我的错误可能在其他地方，但这是我第一次尝试复制缓冲区，所以想检查我是否正确地做这部分。如果有帮助，我的 Mesh 析构函数是：

Mesh::~Mesh() {

    glDeleteVertexArrays(1, &vao);
    glDeleteBuffers(NUM_BUFFERS, vab);

}

通过调试器，我可以看到这当然是在该行之后被调用一次：

this->mesh = Mesh(*texture);

这只是简单地构造一个网格，然后分配它（纹理只是将四边形调整为纹理的大小，并使用正确的顶点位置调用开头显示的构造函数）。

Answer 1

您复制了数组，但从未将复制的版本绑定到 GL_ARRAY_BUFFER，这意味着您的 glVertexAttribPointer 调用没有指向任何内容。

我也对这段代码有点警惕：

glBindBuffer(GL_ARRAY_BUFFER, vab[POSITION_VB]);
glBufferData(GL_ARRAY_BUFFER, nVerts * sizeof (positions[0]), &positions[0], GL_STATIC_DRAW);

glBindBuffer(GL_ARRAY_BUFFER, vab[TEXCOORD_VB]);
glBufferData(GL_ARRAY_BUFFER, nVerts * sizeof (texCoords[0]), &texCoords[0], GL_STATIC_DRAW);

glEnableVertexAttribArray(1);
glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, 0);

glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);

似乎位置顶点指针将引用纹理数据，因为这是您调用glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);时当前绑定的顶点缓冲区

我想你会希望订单是这样的：

glBindBuffer(GL_ARRAY_BUFFER, vab[POSITION_VB]);
glBufferData(GL_ARRAY_BUFFER, nVerts * sizeof (positions[0]), &positions[0], GL_STATIC_DRAW);

glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);

glBindBuffer(GL_ARRAY_BUFFER, vab[TEXCOORD_VB]);
glBufferData(GL_ARRAY_BUFFER, nVerts * sizeof (texCoords[0]), &texCoords[0], GL_STATIC_DRAW);

glEnableVertexAttribArray(1);
glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, 0);

但我不确定。我通常将所有顶点属性交错到一个顶点缓冲区中。