Don't start fading when screen is unredirected

If a window is destroyed and starts to fade out when screen is
unredirected, when the screen become redirected again, we will generate
errors when trying to render that window.

Also make sure the assumption that all window are either MAPPED or
UNMAPPED when screen is unredirected holds.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/compton.c

@@ -2018,11 +2018,7 @@ redir_stop(session_t *ps) {
     for (win *w = ps->list, *next; w; w = next) {
       next = w->next;
       // Wrapping up fading in progress
-      if (w->opacity != w->opacity_tgt) {
-        assert(w->state != WSTATE_UNMAPPED && w->state != WSTATE_MAPPED);
-        w->opacity = w->opacity_tgt;
-        win_check_fade_finished(ps, &w);
-      }
+      win_skip_fading(ps, &w);
 
       // `w` might be freed by win_check_fade_finished
       if (!w) {

src/win.c

@@ -1367,12 +1367,11 @@ finish_destroy_win(session_t *ps, win **_w) {
   win *w = *_w;
   win **prev = NULL;
 
-  // Window can't go from UNMAPPED to DESTROYING, and
-  // UNMAPPED is the only state where the window resource
-  // is freed. That means the window resources have not
-  // been freed at this point. call finish_unmap_win to
-  // free them.
+  if (w->state != WSTATE_UNMAPPED) {
+    // Only UNMAPPED state has window resources freed, otherwise
+    // we need to call finish_unmap_win to free them.
     finish_unmap_win(ps, _w);
+  }
 
   log_trace("Trying to destroy (%#010x)", w->id);
   for (prev = &ps->list; *prev; prev = &(*prev)->next) {
@@ -1477,6 +1476,10 @@ unmap_win(session_t *ps, win **_w, bool destroy) {
     }
   }
 #endif
+
+  if (!ps->redirected) {
+    win_skip_fading(ps, _w);
+  }
 }
 
 /**
@@ -1501,6 +1504,18 @@ win_check_fade_finished(session_t *ps, win **_w) {
   }
 }
 
+/// Skip the current in progress fading of window,
+/// transition the window straight to its end state
+void win_skip_fading(session_t *ps, win **_w) {
+  win *w = *_w;
+  if (w->state == WSTATE_MAPPED || w->state == WSTATE_UNMAPPED) {
+    assert(w->opacity_tgt == w->opacity);
+    return;
+  }
+  w->opacity = w->opacity_tgt;
+  win_check_fade_finished(ps, _w);
+}
+
 /**
  * Get the Xinerama screen a window is on.
  *
@@ -1637,6 +1652,11 @@ map_win(session_t *ps, xcb_window_t id) {
     cdbus_ev_win_mapped(ps, w);
   }
 #endif
+
+  if (!ps->redirected) {
+    win_skip_fading(ps, &w);
+    assert(w);
+  }
 }
 
 

src/win.h

@@ -368,6 +368,10 @@ win_check_fade_finished(session_t *ps, win **_w);
 // Stop receiving events (except ConfigureNotify, XXX why?) from a window
 void win_ev_stop(session_t *ps, win *w);
 
+/// Skip the current in progress fading of window,
+/// transition the window straight to its end state
+void win_skip_fading(session_t *ps, win **_w);
+
 /**
  * Get the leader of a window.
  *