On some circunstances compton will try and set decoration opacity on fullscreen windows

[rechapit]

I managed to produce this issue while trying to run skyrim via wine.
compton will make the upper section of the window transparent where the window decoration would have been if not fullscreen.

the following patch works arround the issue

diff --git a/compton.c b/compton.c
index cffee1a..8f22bb2 100644
--- a/compton.c
+++ b/compton.c
@@ -1150,7 +1150,7 @@ paint_preprocess(session_t *ps, win *list) {
       {
         double frame_opacity_old = w->frame_opacity;

-        if (ps->o.frame_opacity && 1.0 != ps->o.frame_opacity
+        if ((!win_is_fullscreen(ps,w)) && ps->o.frame_opacity && 1.0 != ps->o.frame_opacity
             && win_has_frame(w))
           w->frame_opacity = get_opacity_percent(w) *
             ps->o.frame_opacity; 

[richardgv]

compton relies on _NET_FRAME_EXTENTS to determine the size of window frame, and adjusts when the property changes. If your full-screen window indeed has _NET_FRAME_EXTENTS set, compton is doing what it is supposed to do, and we could never fix a bug in your WM or application. I would recommend you to check _NET_FRAME_EXTENTS on your full-screen window with xprop.

And your patch will unfortunately not be merged into compton. There are cases when a full-screen window has a frame, and the logic doesn't sound like the best solution.