fix problems with settings changed events firing on startup randomly

src/Background/Background.vala

@@ -27,7 +27,7 @@ namespace Gala
 
 		public Meta.Screen screen { get; construct; }
 		public int monitor_index { get; construct; }
-		public Settings settings { get; construct; }
+		public BackgroundSource background_source { get; construct; }
 		public bool is_loaded { get; private set; default = false; }
 		public GDesktop.BackgroundStyle style { get; construct; }
 		public string? filename { get; construct; }
@@ -38,9 +38,14 @@ namespace Gala
 		Cancellable cancellable;
 		uint update_animation_timeout_id = 0;
 
-		public Background (Meta.Screen screen, int monitor_index, string? filename, Settings settings, GDesktop.BackgroundStyle style)
+		public Background (Meta.Screen screen, int monitor_index, string? filename,
+				BackgroundSource background_source, GDesktop.BackgroundStyle style)
 		{
-			Object (screen: screen, monitor_index: monitor_index, settings: settings, style: style, filename: filename);
+			Object (screen: screen,
+					monitor_index: monitor_index,
+					background_source: background_source,
+					style: style,
+					filename: filename);
 		}
 
 		construct
@@ -51,7 +56,7 @@ namespace Gala
 			file_watches = new Gee.HashMap<string,ulong> ();
 			cancellable = new Cancellable ();
 
-			settings.changed.connect (settings_changed);
+			background_source.changed.connect (settings_changed);
 
 			load ();
 		}
@@ -67,7 +72,7 @@ namespace Gala
 				SignalHandler.disconnect (cache, watch);
 			}
 
-			settings.changed.disconnect (settings_changed);
+			background_source.settings.changed.disconnect (settings_changed);
 		}
 
 		public void update_resolution ()
@@ -94,6 +99,7 @@ namespace Gala
 		void load_pattern ()
 		{
 			string color_string;
+			var settings = background_source.settings;
 
 			color_string = settings.get_string ("primary-color");
 			var color = Clutter.Color.from_string (color_string);
@@ -275,7 +281,7 @@ namespace Gala
 				load_file (filename);
 		}
 
-		void settings_changed (Settings settings, string key)
+		void settings_changed ()
 		{
 			changed ();
 		}

src/Background/BackgroundContainer.vala

@@ -42,7 +42,7 @@ namespace Gala
 
 		void update ()
 		{
-			var reference_child = (get_child_at_index (0) as Background);
+			var reference_child = (get_child_at_index (0) as BackgroundManager);
 			if (reference_child != null)
 				reference_child.changed.disconnect (background_changed);
 

src/Background/BackgroundManager.vala

@@ -133,20 +133,24 @@ namespace Gala
 				background_actor.set_position (monitor.x, monitor.y);
 			}
 
-			ulong handler = 0;
-			handler = background.changed.connect (() => {
-				SignalHandler.disconnect (background, handler);
-				handler = 0;
+			ulong changed_handler = 0;
+			changed_handler = background.changed.connect (() => {
+				SignalHandler.disconnect (background, changed_handler);
+				changed_handler = 0;
 				update_background_actor ();
 			});
 
 			background_actor.destroy.connect (() => {
-				if (handler != 0)
-					SignalHandler.disconnect (background, handler);
+				if (changed_handler != 0) {
+					SignalHandler.disconnect (background, changed_handler);
+					changed_handler = 0;
+				}
 
 				var loaded_handler = background.get_data<ulong> ("background-loaded-handler");
-				if (loaded_handler != 0)
+				if (loaded_handler != 0) {
 					SignalHandler.disconnect (background, loaded_handler);
+					background.set_data<ulong> ("background-loaded-handler", 0);
+				}
 			});
 
 			return background_actor;

src/Background/BackgroundSource.vala

@@ -19,6 +19,8 @@ namespace Gala
 {
 	public class BackgroundSource : Object
 	{
+		public signal void changed ();
+
 		public Meta.Screen screen { get; construct; }
 		public Settings settings { get; construct; }
 
@@ -36,6 +38,9 @@ namespace Gala
 			backgrounds = new Gee.HashMap<int,Background> ();
 
 			screen.monitors_changed.connect (monitors_changed);
+
+			settings_hash_cache = get_current_settings_hash_cache ();
+			settings.changed.connect (settings_changed);
 		}
 
 		void monitors_changed ()
@@ -77,7 +82,7 @@ namespace Gala
 				monitor_index = 0;
 
 			if (!backgrounds.has_key (monitor_index)) {
-				var background = new Background (screen, monitor_index, filename, settings, (GDesktop.BackgroundStyle) style);
+				var background = new Background (screen, monitor_index, filename, this, (GDesktop.BackgroundStyle) style);
 
 				background.changed.connect (background_changed);
 
@@ -103,6 +108,55 @@ namespace Gala
 				background.destroy ();
 			}
 		}
+
+		// unfortunately the settings sometimes tend to fire random changes even though
+		// nothing actually happend. The code below is used to prevent us from spamming
+		// new actors all the time, which lead to some problems in other areas of the code
+
+		// helper struct which stores the hash values generated by g_variant_hash
+		struct SettingsHashCache
+		{
+			uint color_shading_type;
+			uint picture_opacity;
+			uint picture_options;
+			uint picture_uri;
+			uint primar_color;
+			uint secondary_color;
+		}
+
+		SettingsHashCache settings_hash_cache;
+
+		// list of keys that are actually relevant for us
+		const string[] options = { "color-shading-type", "picture-opacity",
+				"picture-options", "picture-uri", "primary-color", "secondary-color" };
+
+		void settings_changed (string key)
+		{
+			if (!(key in options))
+				return;
+
+			var current = get_current_settings_hash_cache ();
+
+			if (Memory.cmp (&settings_hash_cache, &current, sizeof (SettingsHashCache)) == 0) {
+				return;
+			}
+
+			Memory.copy (&settings_hash_cache, &current, sizeof (SettingsHashCache));
+
+			changed ();
+		}
+
+		SettingsHashCache get_current_settings_hash_cache ()
+		{
+			return {
+				settings.get_value ("color-shading-type").hash (),
+				settings.get_value ("picture-opacity").hash (),
+				settings.get_value ("picture-options").hash (),
+				settings.get_value ("picture-uri").hash (),
+				settings.get_value ("primary-color").hash (),
+				settings.get_value ("secondary-color").hash ()
+			};
+		}
 	}
 }