opengl - Question about instancing, instanced arrays and buffer updating

Question

In one of my previous questions (How to instance draw with different transformations for multiple objects) I asked how to instance draw with different transformations, one person answered that the proper way to do it is using instanced arrays.

This lead me to tutorials where they send transformation data through VAO, which is exactly what I was looking for.

But a new problem arose. Since my objects are dynamic (I want to move them) how do I update the buffer with their transformation?

Most of the tutorials Ive seen usually only render instanced objects once and thus they have no need to update the buffer. For a fact I wouldnt even know how to update a buffer to begin with, as I declare VAO with mesh at the beginning and it is not changed during the runtime of program.

What I think I should be doing: Store the transformations on CPU side in some array, when I do something which results in changing a specific transformation I will update this array and then update the transformation buffer.

Probably the actual question: How do I update a buffer during the runtime of program?

question from:https://stackoverflow.com/questions/65952279/question-about-instancing-instanced-arrays-and-buffer-updating

Answer 1

Just use glBufferSubData to update the corresponding data on your GPU, from which your shaders get the transformations per instance (e.g. the vertex buffer for which the divisor is set to 1 with glVertexAttribDivisor(idx, 1)).

The other possibility would be to use glMapBuffer or glMapBufferRange to update that buffer.