backend/x11: pause rendering loop when completely hidden

[emersion]

We could stop sending frame events to the compositor when the X11 window is completely hidden.

I'm not sure how we can detect that. Maybe we can detect when we are minimized with Map/Unmap?

glfw seems to be getting the width/height from XGetWindowAttributes, and glfw apps can stop rendering if the size is zero.

---

wlroots has migrated to gitlab.freedesktop.org. This issue has been moved to:

https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/2675

[imirkin]

There's UnmapNotify events, as well as VisibilityNotify which can indicate that a window is fully obscured.

[emersion]

Ah right, VisibilityNotify sounds like the thing one would want to use for pausing rendering loops.

[imirkin]

Well, at least with WindowMaker, I get a UnmapNotify when switching to another workspace.

When I roll up the window, i.e. only the window decoration is visible, I get:

000:>:00f9: Event ConfigureNotify(22) event=0x05c00006 window=0x05c00006 above-sibling=None(0x00000000) x=0 y=-56 width=1024 height=768 border-width=0 override-redirect=false(0x00)
000:>:00f9: Event VisibilityNotify(15) window=0x05c00006 state=PartiallyObscured(0x01)
... whole bunch more ConfigureNotify's with increasingly negative y's ...
000:>:0066: Event UnmapNotify(18) event=0x05c00006 window=0x05c00006 from-configure=false(0x00)

And when I minimize the window, I get an UnmapNotify. So I think it's reasonable to keep track of a "hidden" state with UnmapNotify. Other WM's may behave differently (ultimately this level of control is completely up to the window manager...), but I think such a strategy should be safe. We can add additional cleverness if other WM's follow a different strategy.

FWIW I haven't managed to get WindowMaker to cause a VisibilityNotify = FullyObscured to be generated. Only the partially obscured as it's rolling up the window (which is somewhat of an animation), and unobscured when e.g. mapping the window back in.