>Are you building vertex buffers?
yes
>Are you creating backing layers?
I am not sure what those are.
>Even the immediate mode APIs retain information!
Yes, immediate mode only refers to the way the API is designed, it has nothing to do with how the framework works internally.
>Oh, you can’t paint then scale later? Oh, so to do transparency effects you have to redraw the primitives every frame with new alphas instead of sending a different alpha to your shader? OK. Sure.
Yes, in my implementation, I redraw every primitive every frame.
>What’s your invalidation strategy? You don’t have one because it’s all “immediate,” sure. That’s really interesting. If there’s no performance difference, then well, hmm, why didn’t we do this back in the win32 era?
Because the graphics hardware wasn't there. Todays GPUs are crazy fast, which enables you to just push tens of thousands of vertices to the GPU and be done in less than a millisecond. In the early days this all had to happen on the CPU, which were way too slow for this, so you had to be very careful about what to redraw.