glVertexAttribPointer set to pointer - c++

Question

so I have this class:
class BRENDERDLL_API Vertex
{
private:
glm::vec3 pos;
public:
Vertex(glm::vec3 pos);
~Vertex();
void setPos(glm::vec3 pos);
glm::vec3 getPos();
};
I would want to change:
glm::vec3 pos;
to:
glm::vec3* pos;
Then I need to change:
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
To point somehow where I storage data. There is obviously no problem with first one case, but what to do with second version?
Can I even do that or should I copy data to some array before?

Answer 1

Changing this to glm::vec3* will not benefit you at all, especially in modern GL. What you need to do is create an array of instances of Vertex.
You have to store this stuff in a Vertex Buffer and that means it needs to be laid out "flatly" in memory (e.g. no pointer dereferencing). If you have a contiguous array of Vertex, then you can take the address of the first instance and use glBufferData (...) to upload it to GL-managed memory.
The following code illustrates this:
std::vector <Vertex> verts;
const size_t size = verts.size () * sizeof (Vertex);
// Generate, allocate and upload your array to an OpenGL Buffer Object
GLuint vbo;
glGenBuffers (1, &vbo);
glBindBuffer (GL_ARRAY_BUFFER, vbo);
glBufferData (GL_ARRAY_BUFFER, size, &verts [0], GL_STATIC_DRAW);
// This points to address **0** relative to the buffer currently bound to
// GL_ARRAY_BUFFER.
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);