win: add functions for delayed window updates

And a window update flag for mapping the window.

Also make sure related functions consider the case where the given window
has pending updates.

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

src/compton.c

@@ -1284,6 +1284,12 @@ static void handle_new_windows(session_t *ps) {
 	}
 }
 
+static void refresh_windows(session_t *ps) {
+	win_stack_foreach_managed_safe(w, &ps->window_stack) {
+		win_process_updates(ps, w);
+	}
+}
+
 static void refresh_stale_images(session_t *ps) {
 	win_stack_foreach_managed(w, &ps->window_stack) {
 		win_process_flags(ps, w);
@@ -1328,6 +1334,9 @@ static void handle_pending_updates(EV_P_ struct session *ps) {
 			recheck_focus(ps);
 		}
 
+		// Process window updates
+		refresh_windows(ps);
+
 		// Refresh pixmaps and shadows
 		refresh_stale_images(ps);
 
@@ -1374,11 +1383,14 @@ static void _draw_callback(EV_P_ session_t *ps, int revents attr_unused) {
 
 	if (!was_redirected && ps->redirected) {
 		// paint_preprocess redirected the screen, which might change the state of
-		// some of the windows (e.g. the window image might fail to bind, and the
+		// some of the windows (e.g. the window image might become stale).
-		// window would be put into an error state). so we rerun paint_preprocess
+		// so we rerun _draw_callback to make sure the rendering decision we make
-		// here to make sure the rendering decision we make is up-to-date
+		// is up-to-date, and all the new flags got handled.
-		log_debug("Re-run paint_preprocess");
+		//
-		bottom = paint_preprocess(ps, &fade_running);
+		// TODO This is not ideal, we should try to avoid setting window flags in
+		// paint_preprocess.
+		log_debug("Re-run _draw_callback");
+		return _draw_callback(EV_A_ ps, revents);
 	}
 
 	// Start/stop fade timer depends on whether window are fading

src/event.c

@@ -546,8 +546,8 @@ static inline void ev_property_notify(session_t *ps, xcb_property_notify_event_t
 }
 
 static inline void repair_win(session_t *ps, struct managed_win *w) {
-	if (w->a.map_state != XCB_MAP_STATE_VIEWABLE)
+	// Only mapped window can receive damages
-		return;
+	assert(win_is_mapped_in_x(w));
 
 	region_t parts;
 	pixman_region32_init(&parts);

src/win.c

@@ -1869,6 +1869,7 @@ bool destroy_win_start(session_t *ps, struct win *w) {
 }
 
 void unmap_win_start(session_t *ps, struct managed_win *w) {
+	auto internal_w = (struct managed_win_internal *)w;
 	assert(w);
 	assert(w->base.managed);
 	assert(w->a._class != XCB_WINDOW_CLASS_INPUT_ONLY);
@@ -1881,10 +1882,14 @@ void unmap_win_start(session_t *ps, struct managed_win *w) {
 	}
 
 	if (unlikely(w->state == WSTATE_UNMAPPING || w->state == WSTATE_UNMAPPED)) {
+		if (internal_w->pending_updates & WIN_UPDATE_MAP) {
+			internal_w->pending_updates &= ~(unsigned long)WIN_UPDATE_MAP;
+		} else {
 			log_warn("Trying to unmapping an already unmapped window %#010x "
 			         "\"%s\"",
 			         w->base.id, w->name);
 			assert(false);
+		}
 		return;
 	}
 
@@ -2079,7 +2084,10 @@ void map_win_start(session_t *ps, struct managed_win *w) {
 
 	win_determine_blur_background(ps, w);
 
-	w->ever_damaged = false;
+	// Cannot set w->ever_damaged = false here, since window mapping could be
+	// delayed, so a damage event might have already arrived before this function
+	// is called. But this should be unnecessary in the first place, since
+	// ever_damaged is set to false in unmap_win_finish anyway.
 
 	// We stopped listening on ShapeNotify events
 	// when the window is unmapped (XXX we shouldn't),
@@ -2236,6 +2244,32 @@ win_is_fullscreen_xcb(xcb_connection_t *c, const struct atom *a, const xcb_windo
 	return false;
 }
 
+/// Queue an update on a window. A series of sanity checks are performed
+void win_queue_update(struct managed_win *_w, enum win_update update) {
+	auto w = (struct managed_win_internal *)_w;
+	assert(popcount(update) == 1);
+
+	if (unlikely(_w->state == WSTATE_DESTROYING)) {
+		log_error("Updates queued on a destroyed window %#010x (%s)", _w->base.id,
+		          _w->name);
+		return;
+	}
+
+	w->pending_updates |= WIN_UPDATE_MAP;
+}
+
+/// Process pending updates on a window. Has to be called in X critical section
+void win_process_updates(struct session *ps, struct managed_win *_w) {
+	assert(ps->server_grabbed);
+	auto w = (struct managed_win_internal *)_w;
+
+	if (w->pending_updates & WIN_UPDATE_MAP) {
+		map_win_start(ps, _w);
+	}
+
+	w->pending_updates = 0;
+}
+
 /**
  * Check if a window is a fullscreen window.
  *
@@ -2267,3 +2301,10 @@ win_stack_find_next_managed(const session_t *ps, const struct list_node *i) {
 	}
 	return NULL;
 }
+
+/// Return whether this window is mapped on the X server side
+bool win_is_mapped_in_x(const struct managed_win *w) {
+	auto iw = (const struct managed_win_internal *)w;
+	return w->state == WSTATE_MAPPING || w->state == WSTATE_FADING ||
+	       w->state == WSTATE_MAPPED || (iw->pending_updates & WIN_UPDATE_MAP);
+}

src/win.h

@@ -250,8 +250,12 @@ struct managed_win {
 #endif
 };
 
+/// Process pending updates on a window. Has to be called in X critical section
+void win_process_updates(struct session *ps, struct managed_win *_w);
 /// Process pending images flags on a window. Has to be called in X critical section
 void win_process_flags(session_t *ps, struct managed_win *w);
+/// Queue an update on a window. A series of sanity checks are performed
+void win_queue_update(struct managed_win *_w, enum win_update update);
 
 /// Start the unmap of a window. We cannot unmap immediately since we might need to fade
 /// the window out.
@@ -417,6 +421,9 @@ bool attr_pure win_has_alpha(const struct managed_win *w);
 /// check if reg_ignore_valid is true for all windows above us
 bool attr_pure win_is_region_ignore_valid(session_t *ps, const struct managed_win *w);
 
+/// Whether a given window is mapped on the X server side
+bool win_is_mapped_in_x(const struct managed_win *w);
+
 // Find the managed window immediately below `w` in the window stack
 struct managed_win *attr_pure win_stack_find_next_managed(const session_t *ps,
                                                           const struct list_node *w);

src/win_defs.h

@@ -27,6 +27,11 @@ typedef enum {
 	WMODE_SOLID,              // The window is opaque including the frame
 } winmode_t;
 
+/// Pending window updates
+enum win_update {
+	WIN_UPDATE_MAP = 1,
+};
+
 /// Transition table:
 /// (DESTROYED is when the win struct is destroyed and freed)
 /// ('o' means in all other cases)