Wayland: Restore tablet support and handle multiple tools

[Riteo]

Fixes #88333.

This code was already partially there, although heavily incomplete and nowadays commented out.

It got broken after the WaylandThread refactor and I didn't bother to bring it over, preferring to #if 0 it into oblivion for the time being as I don't have a tablet/pen which support an eraser and tilt reporting.

This commit brings it back and adds proper multi-tool support (needed for eraser detection) thanks to @winston-yallow, who could test this code with their more capable tablet.

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I also noticed some occasional weird segfaults even without even having a tablet installed which I haven't been able to isolate/replicate reliably, so I'm not able to tell if they're a new thing or not.

Although it has been confirmed that eraser and tilt are properly reported now, considering the above, some further testing would be wise.

Here's a nice lil' visualizer I quickly made for this PR, please give it a spin if you have a drawing tablet: https://github.com/riteo/godot-tablet-visualizer

(I wonder if we could make this a demo or something, it's real nifty :D )

[Calinou]

(I wonder if we could make this a demo or something, it's real nifty :D )

I think it makes sense to submit to https://github.com/godotengine/godot-demo-projects, so it can be used as a troubleshooting tool like we do with the Joypads demo.

[akien-mga]

Code looks good to me overall. Haven't tested yet (I have an older laptop with a touchscreen and pen, I'll see if it gets recognized as a tablet). Edit: Pen is out of battery and I don't have any AAAA batteries laying around, so I can't test now :P

I didn't check in detail but the memnew/memdelete stuff around TabletToolState probably needs some caution to avoid double-free or memory leaks (it's good to remember that if it needs to be freed after use, any ERR_FAIL kind of early return need to ensure it gets freed first too).

[Riteo]

@akien-mga

I didn't check in detail but the memnew/memdelete stuff around TabletToolState probably needs some caution to avoid double-free or memory leaks (it's good to remember that if it needs to be freed after use, any ERR_FAIL kind of early return need to ensure it gets freed first too).

Should be good to go already I think, as if there's no godot state set (e.g. libdecor or whatever messing around with our display) it should return null, noopping.

We also memdelete their state only while getting entirely rid of their reference, so we should be fine I think.

I am trying to be as careful as possible on keeping state memory handling as easy and simple as possible without needing full RAII wrappers and whatnot.

[akien-mga]

Should be good to go already I think, as if there's no godot state set (e.g. libdecor or whatever messing around with our display) it should return null, noopping.

Is memdelete(nullptr) safe? I see we have an unused memdelete_notnull macro. We often do if (thing) memdelete(thing); if there's a possibility for the thing to be null.

[Riteo]

@akien-mga Oof it might not be safe :(

Just gave a closer look at the template, and we have this:

if constexpr (!std::is_trivially_destructible_v<T>) {
	p_class->~T();
}

I'll add a null check.

Edit: wait, what about memdelete_notnull? That would avoid indenting too much
Edit2: I also did this assumption thorought the whole thread, we might need a separate PR for that :/

[akien-mga]

Edit: wait, what about memdelete_not_null?

Since it was never used in the codebase, I think for now we should just do the if (thing) memdelete(thing); and discuss with the core team what to do more generally with this pattern.

We could refactor the whole codebase to use memdelete_not_null, or drop the macro and keep doing things ad hoc, or evaluate whether it would be that bad to just add a null check in memdelete itself.

[Riteo]

Should be ready. I can't build it locally right now (low on battery), so a last test would probably be wise.

[akien-mga]

I built and tested af273a1efde392b4ca479b285df5d3047d9504a0 + the hotfix to bring back tool (which you then committed as https://github.com/godotengine/godot/compare/af273a1efde392b4ca479b285df5d3047d9504a0..b01a36b3cd04499d959bbd169dec719e088a420a), so I pretty much tested the latest version of this PR already, ahead of its commit date :P

Also out of battery (AAAA, who uses those anymore aside from Ubisoft...) for my touchscreen pen so I couldn't actually check that the feature works :)

[winston-yallow]

I've tested the most recent version (b01a36b), everything seems to work perfectly.

Device

Wacom Intuos M Pro (2017)

Tilted backwards / right, medium pressure, normal tip:

Tilted backwards / slightly left, high pressure, eraser tip:

[akien-mga]

Thanks!