feh should request Full Screen to the window manager about feh HOT 2 OPEN

Relevant VLC source-code: (probably)

• https://code.videolan.org/videolan/vlc/-/blob/bc0ae4752e63638d5fe16d7304cb0edfa1f8c50f/modules/video_output/xcb/window.c#L704-766
• https://code.videolan.org/videolan/vlc/-/blob/bc0ae4752e63638d5fe16d7304cb0edfa1f8c50f/modules/video_output/xcb/window.c#L941-942

Relevant Feh source-code: (probably)

• feh/src/winwidget.c

  Lines 294 to 309 in 1d02f90

  	if (ret->full_screen) {
  	Atom prop_fs = XInternAtom(disp, "_NET_WM_STATE_FULLSCREEN", False);
  	Atom prop_state = XInternAtom(disp, "_NET_WM_STATE", False);
  	memset(&ev, 0, sizeof(ev));
  	ev.xclient.type = ClientMessage;
  	ev.xclient.message_type = prop_state;
  	ev.xclient.display = disp;
  	ev.xclient.window = ret->win;
  	ev.xclient.format = 32;
  	ev.xclient.data.l[0] = 1;
  	ev.xclient.data.l[1] = prop_fs;
  	XChangeProperty(disp, ret->win, prop_state, XA_ATOM, 32,
  	PropModeReplace, (unsigned char *) &prop_fs, 1);
  	}

• feh/src/winwidget.c

  Lines 344 to 353 in 1d02f90

  	/* Size hints */
  	if (ret->full_screen || opt.geom_flags) {
  	XSizeHints xsz;
  	xsz.flags = USPosition;
  	xsz.x = x;
  	xsz.y = y;
  	XSetWMNormalHints(disp, ret->win, &xsz);
  	XMoveWindow(disp, ret->win, x, y);
  	}

Running xwininfo -wm on VLC (before and after entering full screen):

xwininfo: Window id: 0x5c0000c "rickroll.mp4 - VLC media player"

  Window manager hints:
      Client accepts input or input focus: Yes
      Initial state is Normal State
      Displayed on desktop 0
      Window type:
          Normal
      Process id: 545810 on host foobar
      Frame extents: 0, 0, 28, 0

xwininfo: Window id: 0x5c0000c "rickroll.mp4 - VLC media player"

  Window manager hints:
      Client accepts input or input focus: Yes
      Initial state is Normal State
      Displayed on desktop 0
      Window type:
          Normal
      Window state:
          Fullscreen
          Focused
      Process id: 545810 on host foobar
      Frame extents: 0, 0, 0, 0

Running xwininfo -wm on Feh (before and after entering full screen):

xwininfo: Window id: 0x6200001 "feh [1 of 8] - foobar.jpg"

  No window manager hints defined
  Window manager hints:
      Displayed on desktop 0
      Process id: 550205 on host foobar
      Frame extents: 0, 0, 28, 0

xwininfo: Window id: 0x6200005 "feh [1 of 8] - foobar.jpg"

  No window manager hints defined
  Window manager hints:
      Displayed on desktop 0
      Window state:
          Maximized Vert
          Maximized Horz
          Fullscreen
      Process id: 550205 on host foobar

Somehow, it says "No window manager hints defined" for Feh. This may be a hint to start understanding what is the root cause.

from feh.

When using xprop against both VLC and Feh, I noticed:

• VLC had _NET_WM_STATE(ATOM) = when windowed.
• Feh had _NET_WM_STATE(ATOM) = when windowed.
• VLC had _NET_WM_STATE(ATOM) = _NET_WM_STATE_FULLSCREEN when full screen.
• Feh had _NET_WM_STATE(ATOM) = _NET_WM_STATE_MAXIMIZED_VERT, _NET_WM_STATE_MAXIMIZED_HORZ, _NET_WM_STATE_FULLSCREEN when full screen.
• VLC has _NET_WM_WINDOW_TYPE(ATOM) = _NET_WM_WINDOW_TYPE_NORMAL, while Feh didn't have that hint/prop.
• VLC and Feh had different (hexadecimal) values for _MOTIF_WM_HINTS.

I don't know what else to do. If you can provide a patch (or a branch), I can try compiling it myself and observing if the behavior changes.

from feh.