How do I upload a collection of position vectors and rotation quaternions to the GPU in OpenGL?

Question

First, I upload the mesh of an object to a VAO (which I know how to do) and reuse that data every frame where a new mesh hasn't been introduced.

I want to then use the Vertex Shader to parallelize rotating and translating the many vertices into their real positions, by handing the GPU a position vector and rotation quaternion for each set of data that represents its own contiguous object.

I don't know how to do that second part without making the position and rotation data a uniform upload to the Shader, necessitating a draw call for each contiguous object, which I'm guessing is really inefficient.

Is there any way to upload a series of positions and rotations and tell OpenGL to transform certain sections of the VAO by them?

I tried looking for an answer all day but the documentation is just a bit to confusing for me at the moment.

Here's what my Shader input looks like:

layout (location=0) in vec3 aPos;
layout (location=1) in vec4 aColor;

uniform mat4 uProjection;
uniform mat4 uView;

I'm thinking it would be great to have some form of 'uniform' upload that's only used by a range of vertices when being processed by the GPU, but I'm not sure.

Answer 1

It sounds like you want some data for each "object", rather than for each vertex in the object? You can do this with glVertexAttribDivisor and glDrawArraysInstanced

It could look something like:

1. Create and bind a VAO (glGenVertexArrays, glBindVertexArray)
2. Create and bind a VBO that contains the vertices (glGenBuffers, glBindBuffer, glVertexAttribPointer, glEnableVertexAttribArray, glBufferData)
3. Create and bind a VBO that contains the data that you want per object/instance (same as above, plus glVertexAttribDivisor)

You should call glDrawArraysInstanced rather than glDrawArrays.