How do I structure code with multiple VBOs?

Question

As per my previous question, it seems it would be desirable to use more than a single VBO in my OpenGL program. But I've hit a wall when trying to do this. Currently my main function looks something like this in pseudocode

setup "main" VBO and VAO
load shaders
setup shader attributes

while true
  update geometry into "main" VBO
  glBufferData(... "main" VBO)
  glClear(GL_COLOR_BUFFER_BIT)
  glDrawArrays(...)

Now what I thought I could do is effectively move the setup "main" VBO inside the game loop itself

setup VAO
load shaders
setup shader attributes

while true
  setup "main" VBO
  update geometry into "main" VBO
  glBufferData(... "main" VBO)
  glClear(GL_COLOR_BUFFER_BIT)
  glDrawArrays(...)

which would then allow me to split the loop into multiple chunks, each creating its own VBO and drawing. But this doens't seem to work, and I get a blank white screen. I can only guess this is because the shaders are not only bound to the VAO, but also to the currently active VBO? I've tried glUseProgram() after the "main" VBO setup, but it doesn't seem to help.

I've found it quite difficult to find information regarding which phase exactly depends on which, and in what order things need to be executed.

Answer 1

glBufferData reallocates the VBO in VRAM, use glBufferSubData when updating data.

Generally each mesh has its own VBO(s); and own VAO if not batched. There are optimizations where you use a single VBO for all meshes with the same attribs, etc, but don't worry about that.

The relation of these things is

1. VBO created and loaded with data
2. VAO is bound
3. Vertex attribs are set, vertexAttribPointer points into the current ARRAY_BUFFER, attribs are part of the state of the VAO
4. Program gets vertex attribs from the current VAO (which may be the default VAO 0 if you never bound one)