Windows doesn't care and neither do I. But still, this can be done in immediate mode if the DE can tell the app it wants it to render the window in multiple rec

Windows doesn't care and neither do I. But still, this can be done in immediate mode if the DE can tell the app it wants it to render the window in multiple rectangles with different pixel densities. I have a hope for the whole idea, because imo it could significantly improve text rendering in VR by passing or allowing realtime access to the projection matrix along with the areas to render to. Regular VR compositing distorts text and vector graphics due to reprojection. Plus, as noted above in VRAM speed vs GPU compute speeds, it might actually be faster and more power efficient overall if done right. See e.g. the famous Windows Terminal optimization issue with glyph atlas caching and object reuse.