ozone: overlay candidates

[Bram Stolk]

I am trying to understand the concept of overlay candidates, and the --enable-hardware-overlays flag of chromium.

Ozone has a concept of candidates for overlays.

And the flag mentioned above introduces the concept of overlay strategies.

But is it not up to the display's compositor to decide if and when to use a hardware overlay?

I was expecting that chromium, at most, would just mark surfaces as opaque, and leave the rest to the compositor?

NOTE: I am on linux wayland.

And indeed, I see the Weston compositor use a single HW overlay for the entire chromium browser window, btw. Regardless of what the --enable-hardware-overlays is set to?