[PATCH weston] xwayland: Create the drag-and-drop window in weston_wm_dnd_init

[Derek Foreman]

On 22/02/16 12:42 PM, Carlos Garnacho wrote:
> Just to keep it hidden so far... A lot of the plumbing necessary to
> handle x11->wayland drag and drop is missing, and the current
> partial handling gets in the middle for X11 drag-and-drop itself
> to work.
> 
> The approach is well directed, but needs some further work, till
> then, just keep our fake drag-and-drop target hidden. This allows
> drag-and-drop to work between X11 clients in Xwayland, and avoids
> a crash with (currently unhandled) wl_resource-less data sources.
> 
> Fixes https://bugs.freedesktop.org/show_bug.cgi?id=94218

This seems to be a pretty important stop-gap patch neglected for quite
some time. :(

It looks superficially ok to me, but I'm really not equipped to provide
proper review, I'll happily:
Acked-by: Derek Foreman <derekf at osg.samsung.com>
because I trust Carlos to follow up :)

And maybe if we can get linkmauve to test, as he was the author of the
bug ticket, we can land it?

Thanks,
Derek

> Signed-off-by: Carlos Garnacho <carlosg at gnome.org>
> ---
> 
> I'm sending this patch with the promise to look into improving the
> drag-and-drop interoperation situation at some point before 1.11.
> 
> My intention is copying what mutter is doing currently, and works
> nicely there:
> * Set up an special pointer grab that still relays pointer and
>   keyboard events to the DnD X11 source client, needed as it's
>   still driving DnD as X11 expects of it.
> * Hook to motion events in that grab so we resize/move/map the
>   fake DnD target window to have the same position than the
>   wayland app the pointer is above. That'll make the X11 source
>   side see  something consistent. This is why keeping
>   wm->dnd_window around makes sense IMO.
> * Reply appropriately to XdndPosition/XdndLeave/XdndDrop
>   and translate those to the wayland side.
> 
> But at the moment, I'm doing just the minimals to avoid the crash,
> and allow X11<->X11 drag-and-drop to work.
> 
>  xwayland/dnd.c | 70 ++++++++++++++++++++--------------------------------------
>  1 file changed, 24 insertions(+), 46 deletions(-)
> 
> diff --git a/xwayland/dnd.c b/xwayland/dnd.c
> index f17e4cd..1130f56 100644
> --- a/xwayland/dnd.c
> +++ b/xwayland/dnd.c
> @@ -42,45 +42,6 @@
>  #include "compositor.h"
>  #include "hash.h"
>  
> -static void
> -weston_dnd_start(struct weston_wm *wm, xcb_window_t owner)
> -{
> -	uint32_t values[1], version = 4;
> -
> -	wm->dnd_window = xcb_generate_id(wm->conn);
> -	values[0] =
> -		XCB_EVENT_MASK_SUBSTRUCTURE_NOTIFY |
> -		XCB_EVENT_MASK_PROPERTY_CHANGE;
> -
> -	xcb_create_window(wm->conn,
> -			  XCB_COPY_FROM_PARENT,
> -			  wm->dnd_window,
> -			  wm->screen->root,
> -			  0, 0,
> -			  8192, 8192,
> -			  0,
> -			  XCB_WINDOW_CLASS_INPUT_ONLY,
> -			  wm->screen->root_visual,
> -			  XCB_CW_EVENT_MASK, values);
> -	xcb_change_property(wm->conn,
> -			    XCB_PROP_MODE_REPLACE,
> -			    wm->dnd_window,
> -			    wm->atom.xdnd_aware,
> -			    XCB_ATOM_ATOM,
> -			    32, /* format */
> -			    1, &version);
> -
> -	xcb_map_window(wm->conn, wm->dnd_window);
> -	wm->dnd_owner = owner;
> -}
> -
> -static void
> -weston_dnd_stop(struct weston_wm *wm)
> -{
> -	xcb_destroy_window(wm->conn, wm->dnd_window);
> -	wm->dnd_window = XCB_WINDOW_NONE;
> -}
> -
>  struct dnd_data_source {
>  	struct weston_data_source base;
>  	struct weston_wm *wm;
> @@ -233,12 +194,6 @@ weston_wm_handle_dnd_event(struct weston_wm *wm,
>  
>  		weston_log("XdndSelection owner: %d!\n",
>  			   xfixes_selection_notify->owner);
> -
> -		if (xfixes_selection_notify->owner != XCB_WINDOW_NONE)
> -			weston_dnd_start(wm, xfixes_selection_notify->owner);
> -		else
> -			weston_dnd_stop(wm);
> -
>  		return 1;
>  	}
>  
> @@ -266,7 +221,7 @@ weston_wm_handle_dnd_event(struct weston_wm *wm,
>  void
>  weston_wm_dnd_init(struct weston_wm *wm)
>  {
> -	uint32_t mask;
> +	uint32_t values[1], version = 4, mask;
>  
>  	mask =
>  		XCB_XFIXES_SELECTION_EVENT_MASK_SET_SELECTION_OWNER |
> @@ -274,4 +229,27 @@ weston_wm_dnd_init(struct weston_wm *wm)
>  		XCB_XFIXES_SELECTION_EVENT_MASK_SELECTION_CLIENT_CLOSE;
>  	xcb_xfixes_select_selection_input(wm->conn, wm->selection_window,
>  					  wm->atom.xdnd_selection, mask);
> +
> +	wm->dnd_window = xcb_generate_id(wm->conn);
> +	values[0] =
> +		XCB_EVENT_MASK_SUBSTRUCTURE_NOTIFY |
> +		XCB_EVENT_MASK_PROPERTY_CHANGE;
> +
> +	xcb_create_window(wm->conn,
> +			  XCB_COPY_FROM_PARENT,
> +			  wm->dnd_window,
> +			  wm->screen->root,
> +			  0, 0,
> +			  8192, 8192,
> +			  0,
> +			  XCB_WINDOW_CLASS_INPUT_ONLY,
> +			  wm->screen->root_visual,
> +			  XCB_CW_EVENT_MASK, values);
> +	xcb_change_property(wm->conn,
> +			    XCB_PROP_MODE_REPLACE,
> +			    wm->dnd_window,
> +			    wm->atom.xdnd_aware,
> +			    XCB_ATOM_ATOM,
> +			    32, /* format */
> +			    1, &version);
>  }
>