CODEWITHSUNDEEP
c++opengl
javaLover
javaLover

Reputation: 6425

Where is glVertexAttribDivisor stored - VAO, VBO or global state?

Here is a sample code :- 

unsigned int instanceVBO;
glGenBuffers(1, &instanceVBO);
glBindBuffer(GL_ARRAY_BUFFER, instanceVBO);
glBindVertexArray(VAO);
...
glBufferData(GL_ARRAY_BUFFER, sizeof(glm::vec2) * 100,
       &translations[0], GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0); 
... ... ... 
glEnableVertexAttribArray(2);
glBindBuffer(GL_ARRAY_BUFFER, instanceVBO);
glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(float), (void*)0);
glBindBuffer(GL_ARRAY_BUFFER, 0);   
glVertexAttribDivisor(2, 1);   //<--- who own this setting?
//^ mostly copied from https://learnopengl.com/Advanced-OpenGL/Instancing

Who own the glVertexAttribDivisor setting? (VAO / instanceVBO / global state)

A comment in https://gamedev.stackexchange.com/questions/99236/what-state-is-stored-in-an-opengl-vertex-array-object-vao-and-how-do-i-use-the#comment174555_99238 suggests that it is stored in VBO.

However, the comment contradicts (?) to the above code which calls glVertexAttribDivisor(2, 1) after unbinds glBindBuffer(GL_ARRAY_BUFFER, 0); .

I would be appreciate if you are also kind to provide reference that I can read more about :
which settings/states owned by which one of Opengl's thingy (VAO/VBO/etc).

Upvotes: 1

Views: 580

Answers (1)

Rabbid76
Rabbid76

Reputation: 210908

The vertex array divisor (VERTEX BINDING DIVISOR) is stored in the Vertex Array Objects state vector, separately for each vertex attribute (like enable state, offset, stride etc.).

The states which are stored in the VAO are listed in the specification in Table 23.3: Vertex Array Object State.
VAOs are specified in OpenGL 4.6 API Core Profile Specification - 10.3.1 Vertex Array Objects.

See also Vertex Specification - Instanced arrays

Upvotes: 6

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