Add mouse event pass-through support for window.

[bruvzg]

Adds DisplayServer.window_set_mouse_passthrough function to set polygonal region of the window which accepts mouse events, mouse events outside the region will be passed through to the window behind it.

Region can be drawn using Path2D (or similar) node and set by calling:

DisplayServer.window_set_mouse_passthru($Path2D.curve.get_baked_points())

The same changes for 3.2 are available in click-through-3 branch.

• macOS (implemented and tested on macOS 10.15.5)
• Windows (implemented and tested on Windows 10)
• Linux/X11 (implemented and tested on lubuntu 20.04)

Fixes #39914

[Technohacker]

If there's a sample project available, I can have a test for this on Linux :)

[bruvzg]

Test project (white polygon should be solid, rest of the window click-through): Transo4.zip

[Technohacker]

Testing on Gentoo with KDE Plasma X11, opening the project as-is doesn't seem to be working. Click events don't pass through the window. I might need to check again with the 3.2 branch so I can use the per-pixel alpha to see it clearly

EDIT: Tried it with the 3.2.3 branch from your repository too, same result

EDIT 2: xeyes does work, and it uses the same SHAPE extension too

[Technohacker]

Nevermind, fixed it @bruvzg, you accidentally checked if the extension was not enabled 😂

[Technohacker]

I had @Ashesh3 test it on Windows and it didn't seem to work. I was looking through the MSDN Win32 docs about HTTRANSPARENT and this might be the reason why:

HTTRANSPARENT -1 | In a window currently covered by another window in the same thread (the message will be sent to underlying windows in the same thread until one of them returns a code that is not HTTRANSPARENT).

I didn't see any docs about whether the thread mentioned is the process thread, but I can have another look

[Technohacker]

@bruvzg More documentation diving and I see two possible methods:

1. Use SetRegion to set which area of the window is to be drawn, hence the non-drawn regions will ignore input. The problem with that would be you can't have semi-transparent areas that don't accept input
2. Do our own hit testing and use PostMessage and GetWindow to send the hit test message to the next window below ours if it's outside the polygon. This would allow the semi-transparent overlay with mouse clicks but would need custom code on our side

I could try to implement the second one, since it doesn't force a fully transparent region

[bruvzg]

I had @Ashesh3 test it on Windows and it didn't seem to work. I was looking through the MSDN Win32 docs about HTTRANSPARENT and this might be the reason why

I have tested it on Window 10 too, and it doesn't work.

Do our own hit testing and use PostMessage and GetWindow to send the hit test message to the next window below ours if it's outside the polygon. This would allow the semi-transparent overlay with mouse clicks but would need custom code on our side

Posting just hit test message doesn't work either, maybe forwarding all mouse events and activation messages do (with coordinate conversion, since mouse use client coodrs). Probably this will end up to be extremely complicated and bug prone.

For now, I have changed it to SetWindowRgn with the note about inconsistent behavior in the docs, it should be good enough for most use cases.

[Technohacker]

Yeah I ended up on the same conclusion as well, considering WS_EX_LAYERED worked the same way :)

[akien-mga]

@Technohacker This is now updated if you want to test again on Windows (there's also a 3.2 PR: #40205).

[Technohacker]

Terribly sorry for the delay, had other projects to deal with 😅

Linux X11 KDE Plasma: Working perfectly :)
Windows: Pending

[kiesenverseist]

The feature is one I'm looking forward to, so I thought I'd go ahead and test it on windows. This is my first time compiling godot, so apologies in advance if I did anything incorrectly, but it does work on windows with the given test project.

[akien-mga]

CC @pouleyKetchoupp to review X11 changes.

[pouleyKetchoupp]

Great work!
The X11 code looks fine (apart from the little detail I've pointed out).

I've tested on Ubuntu 20.04:
Gnome - works only with borderless windows.
Plasma - works as intended.

Is the issue with Gnome a deal breaker? I'm not sure what real life use cases are for this feature. If needed, I can help investigate.

[akien-mga]

Suggested change

[akien-mga]

Line == paragraph in the XML.

[akien-mga]

Suggested change

[pouleyKetchoupp]

Summoning ancient horror.

Wow.

If it's mostly used for widgets, I guess it's not a big deal for now if it doesn't play well with window decorations in some cases.

[akien-mga]

Thanks!