I've been delving into OpenGL a while, and now, working on a project, I found that, when I'm creating an index buffer, if I bind it to a GL_ARRAY_BUFFER instead to a GL_ELEMENT_ARRAY_BUFFER has (apparently) the same result.
I mean, the vertex buffers are always bound to GL_ARRAY_BUFFER, but if I create an index buffers like this:
glCreateBuffers(1, &m_BufferID);
glBindBuffer(GL_ARRAY_BUFFER, m_BufferID);
glBufferData(GL_ARRAY_BUFFER, count * sizeof(uint), vertices, GL_STATIC_DRAW);
And then, when drawing geometry for instance, I bind it to a GL_ELEMENT_ARRAY_BUFFER, works just fine, and I don't know why I thought that index buffers had to be created with GL_ELEMENT_ARRAY_BUFFER too, but... Is there any "inner" difference actually?
In terms of the nature of the buffer object itself? No. All buffer objects are the same and can be used for any task appropriate for a buffer object. A buffer object does not take on special properties by which binding it was initially used with.
However, the GL_ELEMENT_ARRAY_BUFFER binding point is itself a bit unusual. It's not part of global context state; it's part of VAO state. So if you have no VAO bound (under a core profile context), then you can't bind anything to that binding point. And when you bind to that binding point, you are affecting the state of the currently bound VAO. And if you change the currently bound VAO, you will be changing which buffer is bound to the element array binding point.
So generally, you should only bind to that point if what you intend to do is attach the buffer to the currently bound VAO.