Bug fix #153: Possible fix for a rare timing issue

Possible fix for a very rare timing issue in focus detection. Compton
may fail to detect the currently focused window, when a window newly
mapped gets focused, we failed to listen to events and get FocusIn from
it in time, and a series of focus change events before it happens stay
in the event queue and puzzled compton. My choice is to force focus
recheck on all focus-related events. More roundtrips to X, but not
necessarily worse performance, due to the high cost of focus flipping
especially when there's a lot of conditions. Thanks to SlackBox for
reporting.  (#153)

Makefile

@@ -49,7 +49,7 @@ ifeq "$(NO_VSYNC_DRM)" ""
   CFG += -DCONFIG_VSYNC_DRM
 endif
 
-# ==== OpenGL VSync ====
+# ==== OpenGL ====
 ifeq "$(NO_VSYNC_OPENGL)" ""
   CFG += -DCONFIG_VSYNC_OPENGL
   # -lGL must precede some other libraries, or it segfaults on FreeBSD (#74)

src/common.h

@@ -30,6 +30,7 @@
 // #define DEBUG_GLX_GLSL   1
 // #define DEBUG_GLX_ERR    1
 // #define DEBUG_GLX_MARK   1
+// #define DEBUG_GLX_PAINTREG 1
 // #define MONITOR_REPAINT  1
 
 // Whether to enable PCRE regular expression support in blacklists, enabled

src/compton.c

@@ -781,6 +781,12 @@ recheck_focus(session_t *ps) {
 
   win *w = find_win_all(ps, wid);
 
+#ifdef DEBUG_EVENTS
+  print_timestamp(ps);
+  printf_dbgf("(): %#010lx (%#010lx \"%s\") focused.\n", wid,
+      (w ? w->id: None), (w ? w->name: NULL));
+#endif
+
   // And we set the focus state here
   if (w) {
     win_set_focused(ps, w, true);
@@ -3815,12 +3821,7 @@ ev_focus_in(session_t *ps, XFocusChangeEvent *ev) {
   ev_focus_report(ev);
 #endif
 
-  if (!ev_focus_accept(ev))
-    return;
-
-  win *w = find_win_all(ps, ev->window);
-  if (w)
-    win_set_focused(ps, w, true);
+  recheck_focus(ps);
 }
 
 inline static void
@@ -3829,12 +3830,7 @@ ev_focus_out(session_t *ps, XFocusChangeEvent *ev) {
   ev_focus_report(ev);
 #endif
 
-  if (!ev_focus_accept(ev))
-    return;
-
-  win *w = find_win_all(ps, ev->window);
-  if (w)
-    win_set_focused(ps, w, false);
+  recheck_focus(ps);
 }
 
 inline static void