Scaling is for legacy apps, right? Modern apps should get the area to render and the desired pixel density.
Not sure what you mean specifically by "need" in "need ... to do compositing". Compositing is just a way (e.g. rerender only on changes, cache results) of running a desktop environment. Strictly speaking you don't need compositing, you can just use immediate mode across the DE and apps.
The tradeoff of course is that if an app is lagging you get a blank rectangle instead of a frozen picture. Well not quite 0 or 1. You can cache lowres and/or compressed frozen picture periodically to improve UX.
> Modern apps should get the area to render and the desired pixel density.
What if you want to smoothly slide an app window over to a second monitor with a different pixel density? That's admittedly a very rare thing, but some people seem to be obsessed with it and insist that it must work. You either have to compose some window surface, or just use clean vector rendering throughout.
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.
Not sure what you mean specifically by "need" in "need ... to do compositing". Compositing is just a way (e.g. rerender only on changes, cache results) of running a desktop environment. Strictly speaking you don't need compositing, you can just use immediate mode across the DE and apps.
The tradeoff of course is that if an app is lagging you get a blank rectangle instead of a frozen picture. Well not quite 0 or 1. You can cache lowres and/or compressed frozen picture periodically to improve UX.