Multithreading yes that works the way you mention but I meant multiple rendering contexts.
In standard OpenGL the de-facto way to do parallel GPU resource uploads while rendering is to have multiple rendering contexts in a "share group" which allows them to share some resources such as textures. So then you can run rendering in one thread that uses one context and do resource uploads in another thread that uses a different context.
There was a sibling comment that mentioned something called off screen canvas which hints that it might be something that would let the web app achieve the same.
In standard OpenGL the de-facto way to do parallel GPU resource uploads while rendering is to have multiple rendering contexts in a "share group" which allows them to share some resources such as textures. So then you can run rendering in one thread that uses one context and do resource uploads in another thread that uses a different context.
There was a sibling comment that mentioned something called off screen canvas which hints that it might be something that would let the web app achieve the same.