can't render more than one mesh

[quinn]

Hi there, your tutorial is excellent, thank you for putting so much work into this. My question is about the Mesh class, I am unable to get it to render multiple meshes. As far as I can tell this is due to the m_vertexArrayObject allocating the same ID for the mesh. Also, i had to make some changes to make this make more sense. For example, I changed m_vertexArrayObject from a GLuint to an array of length one:

enum {
	SINGLE_VAO,
	NUM_VAO
};

GLuint m_vertexArrayObject[NUM_VAO];

glGenVertexArrays(NUM_VAO, m_vertexArrayObject);
glBindVertexArray(m_vertexArrayObject[SINGLE_VAO]);

Secondly, the second argument to glGenVertexArrays is no longer passed as a pointer. Again, this is based on examples I found elsewhere. The problem I am facing is that m_vertexArrayObject[SINGLE_VAO] is always zero (i assume to that being the default value of the array), so (as far as i know) this means I can never have more than one mesh.

Thanks for your help with this!

[lukawarren]

Sorry to bring up an old thread, but I'm having the same issue regarding multiple meshes. Did you ever manage to fix it?

[quinn]

nope. was stumped by this one and gave up learning OpenGL. if you crack it let me know the solution :)

[lukawarren]

Wow how time flies...

I randomly found this old project collecting dust on my hard drive today and remembered getting stuck all those years ago before I'd properly toyed with OpenGL. Facepalmed as soon as I had a look.. turns out the reason I was only seeing "one mesh" was because they both shared the same transform, so completely overlapped :)

For anyone stumbling upon this years later, you'll want each mesh to have its own transform, then update the shader uniforms accordingly:

shader.Bind();
shader.Update(transforms[0], camera);
meshes[0].Draw();

shader.Update(transforms[1], camera);
meshes[1].Draw();

// etc, etc..

Ideally you'd make some sort of "entity" class or struct to make life easier:

struct Entity
{
    Mesh* mesh; // pointer so entities can share meshes
    Transform transform;
}

std::vector<Entity> entities;

// ...

shader.Bind();
for (const auto& entity: entities)
{
    shader.Update(entity.transform, camera);
    entity.mesh->Draw();
}

quinn's issue may be something else, but at least for me it was just a case of "over-debugging"