将 VAO 与 glDrawElements 结合使用

Question

我正在尝试（第一次）使用 OpenGL 3.2 在屏幕上绘制一些精灵。我正在尝试设置一个 VAO，但它不起作用。我在调用 glDrawElements 时收到 EXC_BAD_ACCESS。

VAO 设置：

// setting up VAO

glGenVertexArrays(1, &vao_);

glBindVertexArray(vao_);

glGenBuffers(1, &indices_id_);

glGenBuffers(1, &attributes_id_);

glBindBuffer(GL_ARRAY_BUFFER, attributes_id_);

constexpr GLfloat* ptr = 0;

::glVertexAttribPointer(attribute_position_, 2, GL_FLOAT, false, STRIDE, ptr);
::glVertexAttribPointer(attribute_region_, 2, GL_FLOAT, false, STRIDE, ptr + 2);
::glVertexAttribPointer(attribute_color_, 4, GL_FLOAT, false, STRIDE, ptr + 4);

::glEnableVertexAttribArray(attribute_position_);
::glEnableVertexAttribArray(attribute_region_);
::glEnableVertexAttribArray(attribute_color_);

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indices_id_);

{
    auto data = std::make_unique<short[]>(BATCH_SIZE * 6);

    short j = 0;

    for (std::size_t i = 0; i < BATCH_SIZE * 6; i += 6, j += 4)
    {
        data[i] = j;
        data[i + 1] = (short)(j + 1);
        data[i + 2] = (short)(j + 2);
        data[i + 3] = (short)(j + 2);
        data[i + 4] = (short)(j + 3);
        data[i + 5] = j;
    }

    glBufferData(GL_ELEMENT_ARRAY_BUFFER, static_cast<GLsizeiptr>(BATCH_SIZE * 6 * sizeof(short)), data.get(), GL_STATIC_DRAW);
}

glBindVertexArray(0);

然后在绘图循环的其他地方：

// drawing

glBindVertexArray(vao_);

glBufferData(GL_ARRAY_BUFFER, static_cast<GLsizeiptr>(sizeof(float) * buffer_index_), attributes_.data(), GL_DYNAMIC_DRAW);

glDrawElements(GL_TRIANGLES, static_cast<GLsizei>(6 * number_of_sprites_), GL_UNSIGNED_SHORT, 0);

glBindVertexArray(0);

谁能看出我做错了什么？

更新

我已经添加了建议的更改（非常感谢）。但是，我现在发现我需要在绘图时在 glBindVertexArray(vao_); 之前添加对 glBindBuffer(GL_ARRAY_BUFFER, attributes_id_); 的调用以消除 EXC_BAD_ACCESS 错误。

Answer 1

glBufferData() 期望目标缓冲区作为第一个参数。这里的命名有点混乱，但这意味着您告诉 OpenGL 您指的是哪个绑定缓冲区，而不是缓冲区的 name。这是一个例子：

glBindBuffer(GL_ARRAY_BUFFER, foo); // Binds the buffer named foo to the GL_ARRAY_BUFFER target

glBufferData(GL_ARRAY_BUFFER, ...); // Tells GL you mean the buffer bound to the GL_ARRAY_BUFFER target

Answer 2

OpenGL 4.6 API Core Profile Specification; 10.3. VERTEX ARRAYS; page 347

A vertex array object is created by binding a name returned by GenVertexArrays with the command
void BindVertexArray( uint array );
array is the vertex array object name. The resulting vertex array object is a new state vector, comprising all the state and with the same initial values listed in tables 23.4- 23.7.

Table 23.4 包含 ELEMENT_ARRAY_BUFFER_BINDING

这意味着，绑定 ELEMENT_ARRAY_BUFFER 的状态存储在 Vertex Array Object.

中

在你的情况下 indices_id_ 存储在 vao_ 的状态向量中，因为

glBindVertexArray(vao_);

.....

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indices_id_);

当你打电话时

glBindVertexArray(0);

那么indices_id_不再在当前状态向量中。

您必须更改指令的顺序：

glBindVertexArray(vao_);

.....

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indices_id_);
{
    .....
    glBufferData(indices_id_, static_cast<GLsizeiptr>(BATCH_SIZE * 6), data.get(), GL_STATIC_DRAW);
}
glBindVertexArray(0);

将 VAO 与 glDrawElements 结合使用

Using VAO with glDrawElements

c++

opengl-3

vao