Resizing windows with tablet pen is extremely jerky

[Xyene]

I'm running sway master. If I open a blank workspace and open two apps, resizing them via mouse is smooth/instant. If I do the same with my tablet pen, the resizing is very jerky, and trails the pen position by over a second. Pen movement is otherwise very smooth.

My mouse sends events (as per evhz) at 1000 Hz, while my tablet only at 250 Hz, so if anything it seems like the mouse should place a higher load on sway. I'm not too sure how to go about tracking this down.

I'm happy to provide other information that might be useful.

[Xyene]

The PR I've opened addresses the simple case of resizing a non-v2 surface. With it applied, the problem persists for v2 surfaces (a simple test-case is gedit, which binds tablet v2 handlers).

I've found the cause, but don't know what the most acceptable fix here would be. The root cause is here:

sway/sway/input/cursor.c

Lines 524 to 528 in 2b15cf4

	if (!surface || !wlr_surface_accepts_tablet_v2(tablet->tablet_v2, surface)) {
	wlr_tablet_v2_tablet_tool_notify_proximity_out(sway_tool->tablet_v2_tool);
	cursor_motion(cursor, time_msec, input_device->wlr_device, dx, dy, dx, dy);
	return;
	}

When we're emulating pointer events or are e.g. in the gap between two windows, we call cursor_motion. That eventually calls the seat's motion callback.

sway/sway/input/seatop_default.c

Lines 485 to 488 in 2b15cf4

	cursor_do_rebase(cursor, time_msec, node, surface, sx, sy);
	if (surface && seat_is_input_allowed(cursor->seat, surface)) {
	wlr_seat_pointer_notify_motion(seat->wlr_seat, time_msec, sx, sy);
	}

...which calls cursor_do_rebase that actually handles the resizing.

The problem seems to be that the drag is started with the emulated pointer, but when the tablet pen enters a tablet v2 surface, emulated pointer events stop being generated... so the resize is "stuck".

This means in a layout like the one below, you can only resize the left window by dragging right, and the right window by dragging left, but not the other way (since then the pen would enter the tablet v2 gedit surface).

handle_motion etc. all have calls to wlr_seat_pointer_* in them, so unless I'm missing something a bunch of that code would need to be refactored.

I think it's mainly tricky because the tablet support code tends to directly use a bunch of the mouse code, which tends to work because that mouse code doesn't fire pointer events — but in this case, that doesn't generalize.