pointer moving, clicking doesn't work on headless backend

[cmitsakis]

When using the headless backend, pointer moving and/or clicking with wlrctl doesn't work.

I encountered this issue on cage 0.1.5 and master on Arch Linux. I even tried the cage PR that adds support for wlroots 0.17 and still had the same issue.

I think it's a wlroots issue because it happens on sway too, but I decided to submit it here first (as advised by the wlroots issue tracker instructions). It might be a wlrctl issue too (if there is a wlrctl alternative, let me know and I will test it).

You can test it with this script. It tries to click the "new tab" button on Chrome and takes a screenshot. For me the coordinates of the button are 270 16 but if it doesn't work, check the coordinates of the button on the screenshot.

unset WAYLAND_DISPLAY
export WLR_BACKENDS=headless
export WLR_LIBINPUT_NO_DEVICES=1
cage -- bash -c "
	set -eux
	trap \"exit\" INT TERM
	trap 'kill \$(jobs -p) 2>/dev/null || :' EXIT
	chromium --ozone-platform=wayland --user-data-dir=\"/tmp/temp_chrome_profile\" &
	sleep 1
	wlrctl pointer move -2000 -2000
	sleep 1
	# move pointer to 'New tab' button
	wlrctl pointer move 270 16
	sleep 1
	wlrctl pointer click
	sleep 1
	grim screenshot.png
"

[cmitsakis]

I added -c to the grim command to show the mouse pointer. There is no pointer.

I noticed wlrctl creates a virtual pointer and then destroys it. I modified wlrctl and added some sleep time before it destroys the pointer, and took a screenshot while wlrctl was running and discovered that there is pointer.

Is there a way to keep the pointer after wlrctl exits?

[joggee-fr]

I have tested it using weston-clickdot with WAYLAND_DEBUG=1 environment variable to try to understand what's happening.
Without any modification on wlrctl, I can observe wl_pointer.button event is not sent by the compositor (Cage) to the client (clickdot). If I add a call to wl_display_dispatch() or wl_display_roundtrip() (or just a simple sleep) after zwlr_virtual_pointer_manager_v1_create_virtual_pointer() in wlrctl, the event is well distributed.

I am clearly not a Wayland nor wlroots expert at all, but as I understand it in headless case, no pointer device exists before wlrctl creates a virtual one. Once created, the client (clickdot) get a notification of capabilities update for wl_seat and retrieves a pointer object using wl_seat.get_pointer. It seems that wlroots send pointer events only to client which has requested a pointer object yet. That's where the quick and dirty sleep patch I have tested in wlrctl can make a difference, allowing the client (clickdot) to have time to request a pointer object.

I can't see a reliable way to determine if client is ready to receive pointer events to propose a patch for wlrctl but it is quite interesting.