[MPlayer-dev-eng] Bugreport/Patch: x11 video backend has wrong geometry assumptions

Jens Stimpfle debian at jstimpfle.de
Wed May 8 01:53:58 CEST 2013

I was bitten by a bug while doing some X window management.
>From my program:

static void handle_maprequest(XEvent *ev)

        /* For mplayer, these two lines must be swapped
         * because it ignores any events up to the first
         * MapNotify.
        XMoveResizeWindow(dpy, w, p->x, p->y, p->w, p->h);
        XMapWindow(dpy, w);

static void handle_configurerequest(XEvent *ev)

        /* This does NOT cause a ConfigureNotify event if we already
         * did a handle_maprequest() because the geometry doesn't change.
        XMoveResizeWindow(dpy, w, p->x, p->y, p->w, p->h);

Any events preceding the MapNotify are simply ignored by mplayer. In the
situation above, as long as the geometry doesn't change after the first
map, mplayer won't receive any further ConfigureNotify Events from the X
server and thus output videos under wrong geometry assumptions.

If I swap the two lines from my handle_maprequest() function, the bug
isn't triggered anymore (aside: it's not exactly clean to first map and
then resize).

This patch works for me, and while not an X11 wizard I'm fairly confident it
has no regressions:

--- a/libvo/x11_common.c        2011-12-04 14:30:54.000000000 +0100
+++ b/libvo/x11_common.c        2013-05-08 01:13:36.566182774 +0200
@@ -1148,13 +1148,7 @@
     if (!vo_border) vo_x11_decoration(mDisplay, vo_window, 0);
     // map window
     XMapWindow(mDisplay, vo_window);
-    // wait for map
-    do {
-      XNextEvent(mDisplay, &xev);
-    } while (xev.type != MapNotify || xev.xmap.event != vo_window);
     vo_x11_clearwindow(mDisplay, vo_window);
-    XSelectInput(mDisplay, vo_window, NoEventMask);
-    XSync(mDisplay, False);
     vo_x11_selectinput_witherr(mDisplay, vo_window,
           StructureNotifyMask | KeyPressMask | KeyReleaseMask | PointerMotionMask |
           ButtonPressMask | ButtonReleaseMask | ExposureMask);

Both removed groups of lines do not seem to do anything constructive. The
second group even starts a race condition.

Have a nice day
Jens Stimpfle

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