What happens if you just brute-force and re-render everything when there's a change? I'm all for optimizing but is this really required these days? Even considering laptops and mobile power requirements, rendering off-screen and flipping is lightning fast.
Layout flows are a different matter and can be expensive to compute.
I believe it is not speed, but battery life. Most of the time nothing happens on the screen besides some small widget changing like once per second (e.g. clock), doing 59 full rerenders every second for that (or even more with high refresh rate screens) is significantly higher drain.
But I am absolutely not an expert on this.
Does native OS frameworks have some escape hatch for these slightly changing, constantly damaging elements?
Of course it is. Even if it doesn't matter on your machine, your users will launch your code:
* on a 10 years old PC
* in train on a laptop with 10% battery left
* on a computer with so many things running in the background that you'll be on the edge of thrashing
* on a thermally throttled ultrabook
* on an underpowered SBC
* through foreign CPU arch emulation
* [insert more cases here]
In each of those scenarios, your code will either do its job well or be the source of frustration.