OpenGL - need a simple concept clarification

Question

I\'m new to OpenGL. I understand how to create the vertex and fragments shaders and how to create vertex arrays and put them on the buffer, but how do i link the two? Meanin

Answer 1

There's no really such thing as "currently active buffer". (Well, there is but it's relevant only at the time of VAO specification with the non direct-state-access API.)

The vertex array object (VAO) holds pointers (set through glVertexAttribPointer) into the data within the memory buffers. The bindings to those buffers are a part of the state of the VAO. When you bind a VAO then subsequent glDraw* commands will transfer the vertices from the buffers bound to the current VAO to the pipeline.

For simplicity of comprehension, here is what a VAO roughly is, with the relevant OpenGL 4.5 direct-state-access function names used to set that state:

struct VertexArrayObject
{
    // VertexArrayElementBuffer
    uint element_buffer;

    struct Binding {
        // VertexArrayVertexBuffers
        uint buffer;
        intptr offset;
        sizei stride;

        // VertexArrayBindingDivisor
        uint divisor;
    } bindings[];

    struct Attrib {
        // VertexArrayAttribBinding
        uint binding; // This is an index into bindings[]

        // EnableVertexArrayAttrib
        bool enabled;

        // VertexArrayAttrib*Format
        int size;
        enum type;
        boolean normalized;
        boolean integer;
        boolean long;
        uint relativeoffset;
    } attribs[];
};

When you call glVertexAttribPointer it essentially does the following on the currently bound VAO:

vao.attribs[index].binding = index;
vao.attribs[index].size = size;
vao.attribs[index].type = type;
vao.attribs[index].normalized = normalized;
vao.attribs[index].relativeoffset = 0;
vao.bindings[index].buffer = current ARRAY_BUFFER;
vao.bindings[index].offset = pointer;
vao.bindings[index].stride = stride; // if stride == 0 computes based on size and type