At the end of drag and drop, grab and release seat

[zhuyaliang]

Fix #515

[zhuyaliang]

@cwendling Do you accept this repair method

[zhuyaliang]

@cwendling Looking forward to your review

[cwendling]

What is this nested loop about? Removing it seems logically identical (and working the same) save not being quadratic:

Suggested change

	gboolean viewable = TRUE;
	GtkWidget *tmp = parent;
	while (tmp)
	{
	if (!gtk_widget_get_mapped (tmp))
	{
	viewable = FALSE;
	break;
	}
	tmp = gtk_widget_get_parent (tmp);
	}
	if (viewable)
	xgrab_shell = parent;
	if (gtk_widget_get_mapped (parent))
	xgrab_shell = parent;
	else
	break;

[cwendling]

That's probably sufficient

Suggested change

	GDK_SEAT_CAPABILITY_ALL, TRUE,
	GDK_SEAT_CAPABILITY_ALL_POINTING, TRUE,

[cwendling]

@zhuyaliang I don't like the "fix", but at least it seems to work.

The root issue seems to be inside src/eggtreemultidnd.c's egg_tree_multi_drag_motion_event(), or possibly in how pcmanfm handles drag events.
IIUC it comes from pcmanfm requesting the drag data during drag motion rather than drag drop, but I'm not sure of the implications.
FWIW, File-Roller suffers from the same issue.

[cwendling]

@zhuyaliang are you working on a better fix? I didn't mean to say we mustn't do this, just that it feels like a fairly sad hack. I have however for now no real clue how to fix it properly (save on pcmanfm's side by not querying the data on drag-motion), and probably won't have time to dive into this.
If you feel brave enough to dive in deeper, wonderful! Otherwise, if you feel like it's important to fix this, your hack here seems as good as any -- although it might require extensive testing to see if it has unexpcted side effects.

[zhuyaliang]

@cwendling I suspect that the problem lies within pcmanfm, and I will try to solve it again. If anyone needs this PR during this period, I will open it again
Thank you for your code review and feedback. Due to vacation, I was unable to reply to the message in a timely manner

[zhuyaliang]

@cwendling I tried to fix the problem in libfm but I'm not sure if this fix is correct，Please help review the code

[zhuyaliang]

There are other issues with libfm, which may not be the most perfect fix, but I don't want to invest too much time in libfm. My focus is on mate desktop