Make sure to also reload pre-loaded screens if required

Fixes #39

README.md

@@ -33,8 +33,9 @@ For proxies the recommended setup is to create one game object per screen and pe
 * **Timestep below Popup (number)** - Timestep to set on screen proxy when it is below a popup. This is useful when pausing animations and gameplay while a popup is open.
 * **Transition Url (url)** - Optional URL to call when the screen is about to be shown/hidden. Use this to trigger a transition (see the section on [transitions](#transitions)).
 * **Focus Url (url)** - Optional URL to call when the screen gains or loses focus (see the section on [screen focus](#screen-focus-gainloss)).
+* **Preload (boolean)** - Check this if the screen should be preloaded and kept loaded at all times. For a collection proxy it means that it will be async loaded but not enabled at all times while not visible. This can also temporarily be achieved through the `monarch.preload()` function.
 
-![](docs/setup.png)
+![](docs/setup_proxy.png)
 
 ### Collection factories
 For factories the recommended setup is to create one game object per screen and per game object attach a collection factory component and an instance of the ```screen_factory.script``` provided by Monarch. The ```screen_factory.script``` will take care of the setup of the screen. All you need to do is to make sure that the script properties on the script are correct:
@@ -45,7 +46,14 @@ For factories the recommended setup is to create one game object per screen and
 * **Popup on Popup (boolean)** - Check this if the screen is a [popup](#popups) and it can be shown on top of other popups.
 * **Transition Id (url)** - Optional id of the game object to send a message to when the screen is about to be shown/hidden. Use this to trigger a transition (see the section on [transitions](#transitions)).
 * **Focus Id (url)** - Optional id of the game object to send a message to when the screen gains or loses focus (see the section on [screen focus](#screen-focus-gainloss)).
+* **Preload (boolean)** - Check this if the screen should be preloaded and kept loaded at all times. For a collection factory this means that its resources will be dynamically loaded at all times. This can also temporarily be achieved through the `monarch.preload()` function.
 
+![](docs/setup_factory.png)
+
+Note: Monarch supports dynamic collection factories (ie where the "Load Dynamically" checkbox is checked).
+
+## Nesting screens
+Sometimes it might be desirable to have a screen that contains one or more sub-screens or children, for instance popups that are used only by that screen. Monarch supports nested screens only when the parent screen is created via a collection factory. If the parent screen is loaded via a collection proxy the sub/child-screens won't be able to receive any input.
 
 ## Navigating between screens
 The navigation in Monarch is based around a stack of screens. When a screen is shown it is pushed to the top of the stack. When going back to a previous screen the topmost screen on the stack is removed. Example:
@@ -88,6 +96,15 @@ As opposed to if the ```clear``` flag was not set:
 * A call to ```monarch.show(B, { clear = false })``` is made
 * Stack is ```[A, B, C, D, B]``` - (B is on top)
 
+#### Showing a screen without adding it to the stack
+Monarch can also show a screen without adding it to the stack. This can be used to for instance load a collection containing a background that you want to have visible at all times. You show and hide such a screen like this:
+
+	-- show the background without adding it to the stack
+	monarch.show(hash("background"), { no_stack = true })
+
+	-- hide the background
+	monarch.hide(hash("background"))
+
 ### Going back to a previous screen
 You navigate back in the screen hierarchy in one of two ways:
 
@@ -279,13 +296,25 @@ Show a Monarch screen. Note that the screen must be registered before it can be
 
 The options table can contain the following fields:
 
-* ```clear``` (boolean) - If the clear flag is set Monarch will search the stack for the screen that is to be shown. If the screen already exists in the stack and the clear flag is set Monarch will remove all screens between the current top and the screen in question.
-* ```reload``` (boolean) - If the reload flag is set Monarch will reload the collection proxy if it's already loaded (this can happen if the previous screen was a popup).
+* ```clear``` (boolean) - If the `clear` flag is set Monarch will search the stack for the screen that is to be shown. If the screen already exists in the stack and the clear flag is set Monarch will remove all screens between the current top and the screen in question.
+* ```reload``` (boolean) - If the `reload` flag is set Monarch will reload the collection proxy if it's already loaded (this can happen if the previous screen was a popup).
+* ```no_stack``` (boolean) - If the `no_stack` flag is set Monarch will load the screen without adding it to the screen stack.
 
 **RETURN**
 * ```success``` (boolean) - True if the process of showing the screen was started successfully. False if already busy showing/hiding a screen.
 
 
+### monarch.hide(screen_id, [callback])
+Hide a screen that has been shown using the `no_stack` option. If used on a screen that was shown without the `no_stack` option it will only hide it if the screen is on top of the stack and the behavior will be exactly like if `monarch.back()` had been called.
+
+**PARAMETERS**
+* ```screen_id``` (hash) - Id of the screen to hide.
+* ```callback``` (function) - Optional function to call when the screen has been hidden.
+
+**RETURN**
+* ```success``` (boolean) - True if the process of hiding the screen was started successfully.
+
+
 ### monarch.back([data], [callback])
 Go back to a previous Monarch screen
 
@@ -302,7 +331,15 @@ Preload a Monarch screen. This will load but not enable the screen. This is usef
 
 **PARAMETERS**
 * ```screen_id``` (hash) - Id of the screen to preload.
-* ```callback``` (function) - Optional function to call when the new screen is preloaded.
+* ```callback``` (function) - Optional function to call when the screen is preloaded.
+
+
+### monarch.unload(screen_id, [callback])
+Unload a preloaded Monarch screen. A preloaded screen will automatically get unloaded when hidden, but this function can be useful if a screen has been preloaded and it needs to be unloaded again.
+
+**PARAMETERS**
+* ```screen_id``` (hash) - Id of the screen to unload.
+* ```callback``` (function) - Optional function to call when the screen is unloaded.
 
 
 ### monarch.top([offset])
@@ -352,6 +389,26 @@ Check if Monarch is busy showing and/or hiding a screen.
 * ```busy``` (boolean) - True if busy hiding and/or showing a screen.
 
 
+### monarch.is_top(id)
+Check if a Monarch screen is at the top of the view stack.
+
+**PARAMETERS**
+* ```screen_id``` (hash) - Id of the screen to check
+
+**RETURN**
+* ```exists``` (boolean) - True if the screen is at the top of the stack.
+
+
+### monarch.is_visible(id)
+Check if a Monarch screen is visible.
+
+**PARAMETERS**
+* ```screen_id``` (hash) - Id of the screen to check
+
+**RETURN**
+* ```exists``` (boolean) - True if the screen is visible.
+
+
 ### monarch.add_listener([url])
 Add a URL that will be notified of navigation events.
 

assets/logo.atlas

@@ -0,0 +1,6 @@
+images {
+  image: "/assets/images/logo.png"
+}
+margin: 0
+extrude_borders: 0
+inner_padding: 0

example/background.collection

@@ -0,0 +1,42 @@
+name: "background"
+scale_along_z: 0
+embedded_instances {
+  id: "go"
+  data: "embedded_components {\n"
+  "  id: \"sprite\"\n"
+  "  type: \"sprite\"\n"
+  "  data: \"tile_set: \\\"/assets/logo.atlas\\\"\\n"
+  "default_animation: \\\"logo\\\"\\n"
+  "material: \\\"/builtins/materials/sprite.material\\\"\\n"
+  "blend_mode: BLEND_MODE_ALPHA\\n"
+  "\"\n"
+  "  position {\n"
+  "    x: 0.0\n"
+  "    y: 0.0\n"
+  "    z: 0.0\n"
+  "  }\n"
+  "  rotation {\n"
+  "    x: 0.0\n"
+  "    y: 0.0\n"
+  "    z: 0.0\n"
+  "    w: 1.0\n"
+  "  }\n"
+  "}\n"
+  ""
+  position {
+    x: 320.0
+    y: 568.0
+    z: 0.0
+  }
+  rotation {
+    x: 0.0
+    y: 0.0
+    z: 0.0
+    w: 1.0
+  }
+  scale3 {
+    x: 1.0
+    y: 1.0
+    z: 1.0
+  }
+}

example/example.collection

@@ -3,8 +3,8 @@ scale_along_z: 0
 embedded_instances {
   id: "menu"
   data: "components {\n"
-  "  id: \"screen\"\n"
-  "  component: \"/monarch/screen_proxy.script\"\n"
+  "  id: \"screen_factory\"\n"
+  "  component: \"/monarch/screen_factory.script\"\n"
   "  position {\n"
   "    x: 0.0\n"
   "    y: 0.0\n"
@@ -22,26 +22,21 @@ embedded_instances {
   "    type: PROPERTY_TYPE_HASH\n"
   "  }\n"
   "  properties {\n"
-  "    id: \"timestep_below_popup\"\n"
-  "    value: \"0.0\"\n"
-  "    type: PROPERTY_TYPE_NUMBER\n"
+  "    id: \"transition_id\"\n"
+  "    value: \"/go\"\n"
+  "    type: PROPERTY_TYPE_HASH\n"
   "  }\n"
   "  properties {\n"
-  "    id: \"transition_url\"\n"
-  "    value: \"menu:/go#menu\"\n"
-  "    type: PROPERTY_TYPE_URL\n"
-  "  }\n"
-  "  properties {\n"
-  "    id: \"focus_url\"\n"
-  "    value: \"menu:/go#menu\"\n"
-  "    type: PROPERTY_TYPE_URL\n"
+  "    id: \"focus_id\"\n"
+  "    value: \"/go\"\n"
+  "    type: PROPERTY_TYPE_HASH\n"
   "  }\n"
   "}\n"
   "embedded_components {\n"
-  "  id: \"collectionproxy\"\n"
-  "  type: \"collectionproxy\"\n"
-  "  data: \"collection: \\\"/example/menu.collection\\\"\\n"
-  "exclude: false\\n"
+  "  id: \"collectionfactory\"\n"
+  "  type: \"collectionfactory\"\n"
+  "  data: \"prototype: \\\"/example/menu.collection\\\"\\n"
+  "load_dynamically: true\\n"
   "\"\n"
   "  position {\n"
   "    x: 0.0\n"
@@ -249,84 +244,6 @@ embedded_instances {
     z: 1.0
   }
 }
-embedded_instances {
-  id: "popup"
-  data: "components {\n"
-  "  id: \"screen\"\n"
-  "  component: \"/monarch/screen_factory.script\"\n"
-  "  position {\n"
-  "    x: 0.0\n"
-  "    y: 0.0\n"
-  "    z: 0.0\n"
-  "  }\n"
-  "  rotation {\n"
-  "    x: 0.0\n"
-  "    y: 0.0\n"
-  "    z: 0.0\n"
-  "    w: 1.0\n"
-  "  }\n"
-  "  properties {\n"
-  "    id: \"screen_id\"\n"
-  "    value: \"popup\"\n"
-  "    type: PROPERTY_TYPE_HASH\n"
-  "  }\n"
-  "  properties {\n"
-  "    id: \"popup\"\n"
-  "    value: \"true\"\n"
-  "    type: PROPERTY_TYPE_BOOLEAN\n"
-  "  }\n"
-  "  properties {\n"
-  "    id: \"popup_on_popup\"\n"
-  "    value: \"true\"\n"
-  "    type: PROPERTY_TYPE_BOOLEAN\n"
-  "  }\n"
-  "  properties {\n"
-  "    id: \"transition_id\"\n"
-  "    value: \"/go\"\n"
-  "    type: PROPERTY_TYPE_HASH\n"
-  "  }\n"
-  "  properties {\n"
-  "    id: \"focus_id\"\n"
-  "    value: \"/go\"\n"
-  "    type: PROPERTY_TYPE_HASH\n"
-  "  }\n"
-  "}\n"
-  "embedded_components {\n"
-  "  id: \"collectionfactory\"\n"
-  "  type: \"collectionfactory\"\n"
-  "  data: \"prototype: \\\"/example/popup.collection\\\"\\n"
-  "load_dynamically: false\\n"
-  "\"\n"
-  "  position {\n"
-  "    x: 0.0\n"
-  "    y: 0.0\n"
-  "    z: 0.0\n"
-  "  }\n"
-  "  rotation {\n"
-  "    x: 0.0\n"
-  "    y: 0.0\n"
-  "    z: 0.0\n"
-  "    w: 1.0\n"
-  "  }\n"
-  "}\n"
-  ""
-  position {
-    x: 0.0
-    y: 0.0
-    z: 0.0
-  }
-  rotation {
-    x: 0.0
-    y: 0.0
-    z: 0.0
-    w: 1.0
-  }
-  scale3 {
-    x: 1.0
-    y: 1.0
-    z: 1.0
-  }
-}
 embedded_instances {
   id: "about"
   data: "components {\n"
@@ -363,6 +280,11 @@ embedded_instances {
   "    value: \"about:/go#about\"\n"
   "    type: PROPERTY_TYPE_URL\n"
   "  }\n"
+  "  properties {\n"
+  "    id: \"preload\"\n"
+  "    value: \"true\"\n"
+  "    type: PROPERTY_TYPE_BOOLEAN\n"
+  "  }\n"
   "}\n"
   "embedded_components {\n"
   "  id: \"collectionproxy\"\n"
@@ -473,3 +395,61 @@ embedded_instances {
     z: 1.0
   }
 }
+embedded_instances {
+  id: "background"
+  data: "components {\n"
+  "  id: \"screen_factory\"\n"
+  "  component: \"/monarch/screen_factory.script\"\n"
+  "  position {\n"
+  "    x: 0.0\n"
+  "    y: 0.0\n"
+  "    z: 0.0\n"
+  "  }\n"
+  "  rotation {\n"
+  "    x: 0.0\n"
+  "    y: 0.0\n"
+  "    z: 0.0\n"
+  "    w: 1.0\n"
+  "  }\n"
+  "  properties {\n"
+  "    id: \"screen_id\"\n"
+  "    value: \"background\"\n"
+  "    type: PROPERTY_TYPE_HASH\n"
+  "  }\n"
+  "}\n"
+  "embedded_components {\n"
+  "  id: \"collectionfactory\"\n"
+  "  type: \"collectionfactory\"\n"
+  "  data: \"prototype: \\\"/example/background.collection\\\"\\n"
+  "load_dynamically: false\\n"
+  "\"\n"
+  "  position {\n"
+  "    x: 0.0\n"
+  "    y: 0.0\n"
+  "    z: 0.0\n"
+  "  }\n"
+  "  rotation {\n"
+  "    x: 0.0\n"
+  "    y: 0.0\n"
+  "    z: 0.0\n"
+  "    w: 1.0\n"
+  "  }\n"
+  "}\n"
+  ""
+  position {
+    x: 0.0
+    y: 0.0
+    z: 0.0
+  }
+  rotation {
+    x: 0.0
+    y: 0.0
+    z: 0.0
+    w: 1.0
+  }
+  scale3 {
+    x: 1.0
+    y: 1.0
+    z: 1.0
+  }
+}

example/main.script

@@ -8,6 +8,8 @@ end
 
 function on_message(self, message_id, message, sender)
 	if message_id == hash("init_monarch") then
-		monarch.show(hash("menu"))
+		monarch.show(hash("background"), { no_stack = true }, nil, function()
+			monarch.show(hash("menu"))
+		end)
 	end
 end

example/menu.collection

@@ -35,3 +35,81 @@ embedded_instances {
     z: 1.0
   }
 }
+embedded_instances {
+  id: "popup"
+  data: "components {\n"
+  "  id: \"screen\"\n"
+  "  component: \"/monarch/screen_factory.script\"\n"
+  "  position {\n"
+  "    x: 0.0\n"
+  "    y: 0.0\n"
+  "    z: 0.0\n"
+  "  }\n"
+  "  rotation {\n"
+  "    x: 0.0\n"
+  "    y: 0.0\n"
+  "    z: 0.0\n"
+  "    w: 1.0\n"
+  "  }\n"
+  "  properties {\n"
+  "    id: \"screen_id\"\n"
+  "    value: \"popup\"\n"
+  "    type: PROPERTY_TYPE_HASH\n"
+  "  }\n"
+  "  properties {\n"
+  "    id: \"popup\"\n"
+  "    value: \"true\"\n"
+  "    type: PROPERTY_TYPE_BOOLEAN\n"
+  "  }\n"
+  "  properties {\n"
+  "    id: \"popup_on_popup\"\n"
+  "    value: \"true\"\n"
+  "    type: PROPERTY_TYPE_BOOLEAN\n"
+  "  }\n"
+  "  properties {\n"
+  "    id: \"transition_id\"\n"
+  "    value: \"/go\"\n"
+  "    type: PROPERTY_TYPE_HASH\n"
+  "  }\n"
+  "  properties {\n"
+  "    id: \"focus_id\"\n"
+  "    value: \"/go\"\n"
+  "    type: PROPERTY_TYPE_HASH\n"
+  "  }\n"
+  "}\n"
+  "embedded_components {\n"
+  "  id: \"collectionfactory\"\n"
+  "  type: \"collectionfactory\"\n"
+  "  data: \"prototype: \\\"/example/popup.collection\\\"\\n"
+  "load_dynamically: false\\n"
+  "\"\n"
+  "  position {\n"
+  "    x: 0.0\n"
+  "    y: 0.0\n"
+  "    z: 0.0\n"
+  "  }\n"
+  "  rotation {\n"
+  "    x: 0.0\n"
+  "    y: 0.0\n"
+  "    z: 0.0\n"
+  "    w: 1.0\n"
+  "  }\n"
+  "}\n"
+  ""
+  position {
+    x: 0.0
+    y: 0.0
+    z: 0.0
+  }
+  rotation {
+    x: 0.0
+    y: 0.0
+    z: 0.0
+    w: 1.0
+  }
+  scale3 {
+    x: 1.0
+    y: 1.0
+    z: 1.0
+  }
+}

monarch/monarch.lua

@@ -11,6 +11,7 @@ local ACQUIRE_INPUT_FOCUS = hash("acquire_input_focus")
 local ASYNC_LOAD = hash("async_load")
 local UNLOAD = hash("unload")
 local ENABLE = hash("enable")
+local DISABLE = hash("disable")
 
 -- transition messages
 M.TRANSITION = {}
@@ -112,6 +113,17 @@ function M.is_top(id)
 end
 
 
+--- Check if a screen is visible
+-- @param id (string|hash)
+-- @return true if the screen is visible
+function M.is_visible(id)
+	assert(id, "You must provide a screen id")
+	id = tohash(id)
+	assert(screens[id], ("There is no screen registered with id %s"):format(tostring(id)))
+	return screens[id].loaded
+end
+
+
 local function register(id, settings)
 	assert(id, "You must provide a screen id")
 	id = tohash(id)
@@ -142,12 +154,17 @@ end
 -- 		* focus_url - URL to a script that is to be notified of focus
 --		  lost/gained events
 --		* timestep_below_popup - Timestep to set on proxy when below a popup
+--		* auto_preload - true if the screen should be automatically preloaded
 function M.register_proxy(id, proxy, settings)
 	assert(proxy, "You must provide a collection proxy URL")
 	local screen = register(id, settings)
 	screen.proxy = proxy
 	screen.transition_url = settings and settings.transition_url
 	screen.focus_url = settings and settings.focus_url
+	screen.auto_preload = settings and settings.auto_preload
+	if screen.auto_preload then
+		M.preload(id)
+	end
 end
 M.register = M.register_proxy
 
@@ -167,12 +184,17 @@ M.register = M.register_proxy
 --		  for the screen transitions
 -- 		* focus_id - Id of the game object in the collection that is to be notified
 --		  of focus lost/gained events
+--		* auto_preload - true if the screen should be automatically preloaded
 function M.register_factory(id, factory, settings)
 	assert(factory, "You must provide a collection factory URL")
 	local screen = register(id, settings)
 	screen.factory = factory
 	screen.transition_id = settings and settings.transition_id
 	screen.focus_id = settings and settings.focus_id
+	screen.auto_preload = settings and settings.auto_preload
+	if screen.auto_preload then
+		M.preload(id)
+	end
 end
 
 --- Unregister a screen
@@ -221,22 +243,35 @@ local function change_context(screen)
 	screen.wait_for = nil
 end
 
-local function unload(screen)
+local function unload(screen, force)
 	log("unload()", screen.id)
 
 	if screen.proxy then
-		screen.wait_for = PROXY_UNLOADED
-		msg.post(screen.proxy, UNLOAD)
-		coroutine.yield()
-		screen.loaded = false
-		screen.wait_for = nil
+		if screen.auto_preload and not force then
+			msg.post(screen.proxy, DISABLE)
+			screen.loaded = false
+			screen.preloaded = true
+		else
+			screen.wait_for = PROXY_UNLOADED
+			msg.post(screen.proxy, UNLOAD)
+			coroutine.yield()
+			screen.loaded = false
+			screen.preloaded = false
+			screen.wait_for = nil
+		end
 	elseif screen.factory then
 		for id, instance in pairs(screen.factory_ids) do
 			go.delete(instance)
 		end
 		screen.factory_ids = nil
-		collectionfactory.unload(screen.factory)
-		screen.loaded = false
+		if screen.auto_preload and not force then
+			screen.loaded = false
+			screen.preloaded = true
+		else
+			collectionfactory.unload(screen.factory)
+			screen.loaded = false
+			screen.preloaded = false
+		end
 	end
 end
 
@@ -273,7 +308,7 @@ end
 local function load(screen)
 	log("load()", screen.id)
 	assert(screen.co, "You must assign a coroutine to the screen")
-	
+
 	if screen.loaded then
 		log("load() screen already loaded", screen.id)
 		return
@@ -285,7 +320,7 @@ local function load(screen)
 		log("load() screen wasn't preloaded", screen.id)
 		return
 	end
-	
+
 	if screen.proxy then
 		msg.post(screen.proxy, ENABLE)
 	elseif screen.factory then
@@ -404,7 +439,7 @@ local function show_out(screen, next_screen, cb)
 	coroutine.resume(co)
 end
 
-local function show_in(screen, previous_screen, reload, cb)
+local function show_in(screen, previous_screen, reload, add_to_stack, cb)
 	log("show_in()", screen.id)
 	local co
 	co = coroutine.create(function()
@@ -414,10 +449,12 @@ local function show_in(screen, previous_screen, reload, cb)
 		change_context(screen)
 		if reload and screen.loaded then
 			log("show_in() reloading", screen.id)
-			unload(screen)
+			unload(screen, reload)
 		end
 		load(screen)
-		stack[#stack + 1] = screen
+		if add_to_stack then
+			stack[#stack + 1] = screen
+		end
 		reset_timestep(screen)
 		transition(screen, M.TRANSITION.SHOW_IN, { previous_screen = previous_screen and previous_screen.id })
 		acquire_input(screen)
@@ -522,7 +559,7 @@ function M.show(id, options, data, cb)
 	end
 
 	local callbacks = callback_tracker()
-	
+
 	id = tohash(id)
 	assert(screens[id], ("There is no screen registered with id %s"):format(tostring(id)))
 
@@ -531,45 +568,88 @@ function M.show(id, options, data, cb)
 
 	log("show()", screen.id)
 
-	-- manipulate the current top
-	-- close popup if needed
-	-- transition out
-	local top = stack[#stack]
-	if top then
-		-- keep top popup visible if new screen can be shown on top of a popup
-		if top.popup and screen.popup_on_popup then
-			disable(top, screen)
-		else
-			-- close all popups
-			while top.popup do
-				stack[#stack] = nil
-				show_out(top, screen, callbacks.track())
-				top = stack[#stack]
-			end
-			-- unload and transition out from top
-			-- unless we're showing the same screen as is already visible
-			if top and top.id ~= screen.id then
-				show_out(top, screen, callbacks.track())
+	local co
+	co = coroutine.create(function()
+		-- a screen can ignore the stack by setting the no_stack to true
+		local add_to_stack = not options or not options.no_stack
+		if add_to_stack then
+			-- manipulate the current top
+			-- close popup(s) if needed
+			-- transition out
+			local top = stack[#stack]
+			if top then
+				-- keep top popup visible if new screen can be shown on top of a popup
+				if top.popup and screen.popup_on_popup then
+					disable(top, screen)
+				else
+					-- close all popups, one by one
+					while top.popup do
+						stack[#stack] = nil
+						show_out(top, screen, function()
+							coroutine.resume(co)
+						end)
+						coroutine.yield()
+						top = stack[#stack]
+					end
+					-- unload and transition out from top
+					-- unless we're showing the same screen as is already visible
+					if top and top.id ~= screen.id then
+						show_out(top, screen, callbacks.track())
+					end
+				end
 			end
 		end
-	end
 
-	-- if the screen we want to show is in the stack
-	-- already and the clear flag is set then we need
-	-- to remove every screen on the stack up until and
-	-- including the screen itself
-	if options and options.clear then
-		log("show() clearing")
-		while M.in_stack(id) do
-			table.remove(stack)
+		-- if the screen we want to show is in the stack
+		-- already and the clear flag is set then we need
+		-- to remove every screen on the stack up until and
+		-- including the screen itself
+		if options and options.clear then
+			log("show() clearing")
+			while M.in_stack(id) do
+				table.remove(stack)
+			end
+		end
+
+		-- show screen
+		show_in(screen, top, options and options.reload, add_to_stack, callbacks.track())
+
+		if cb then callbacks.when_done(cb) end
+	end)
+	coroutine.resume(co)
+
+	return true
+end
+
+
+-- Hide a screen. The screen must either be at the top of the stack or
+-- visible but not added to the stack (through the no_stack option)
+-- @param id (string|hash) - Id of the screen to show
+-- @param cb (function) - Optional callback to invoke when the screen is hidden
+-- @return true if successfully hiding, false if busy performing another operation
+function M.hide(id, cb)
+	if M.is_busy() then
+		log("hide() monarch is busy, ignoring request")
+		return false
+	end
+	
+	id = tohash(id)
+	assert(screens[id], ("There is no screen registered with id %s"):format(tostring(id)))
+
+	local screen = screens[id]
+	if M.in_stack(id) then
+		if not M.is_top(id) then
+			log("hide() you can only hide the screen at the top of the stack", id)
+			return false
+		end
+		return M.back(id, cb)
+	else
+		if M.is_visible(id) then
+			back_out(screen, nil, cb)
+		elseif cb then
+			cb()
 		end
 	end
-
-	-- show screen
-	show_in(screen, top, options and options.reload, callbacks.track())
-
-	if cb then callbacks.when_done(cb) end
-
 	return true
 end
 
@@ -585,7 +665,7 @@ function M.back(data, cb)
 	end
 
 	local callbacks = callback_tracker()
-	
+
 	local screen = table.remove(stack)
 	if screen then
 		log("back()", screen.id)
@@ -611,7 +691,7 @@ function M.back(data, cb)
 	end
 
 	if cb then callbacks.when_done(cb) end
-	
+
 	return true
 end
 
@@ -621,6 +701,11 @@ end
 -- @param id (string|hash) - Id of the screen to preload
 -- @param cb (function) - Optional callback to invoke when screen is loaded
 function M.preload(id, cb)
+	if M.is_busy() then
+		log("preload() monarch is busy, ignoring request")
+		return false
+	end
+
 	assert(id, "You must provide a screen id")
 	id = tohash(id)
 	assert(screens[id], ("There is no screen registered with id %s"):format(tostring(id)))
@@ -629,16 +714,50 @@ function M.preload(id, cb)
 	log("preload()", screen.id)
 	if screen.preloaded or screen.loaded then
 		if cb then cb() end
-		return
+		return true
 	end
 	local co
 	co = coroutine.create(function()
 		screen.co = co
 		change_context(screen)
 		preload(screen)
+		log("preload() done", screen.id)
 		if cb then cb() end
 	end)
 	assert(coroutine.resume(co))
+	return true
+end
+
+
+function M.unload(id, cb)
+	if M.is_busy() then
+		log("unload() monarch is busy, ignoring request")
+		return false
+	end
+	assert(id, "You must provide a screen id")
+	id = tohash(id)
+	assert(screens[id], ("There is no screen registered with id %s"):format(tostring(id)))
+
+	if M.is_visible(id) then
+		log("You can't unload a visible screen")
+		return false
+	end
+
+	local screen = screens[id]
+	if not screen.preloaded and not screen.loaded then
+		log("unload() screen is not loaded", tostring(id))
+		if cb then cb() end
+		return true
+	end
+	local co
+	co = coroutine.create(function()
+		screen.co = co
+		change_context(screen)
+		unload(screen)
+		if cb then cb() end
+	end)
+	assert(coroutine.resume(co))
+	return true
 end
 
 

monarch/screen_factory.script

@@ -6,6 +6,7 @@ go.property("popup", false)
 go.property("popup_on_popup", false)
 go.property("transition_id", hash(""))
 go.property("focus_id", hash(""))
+go.property("preload", false)
 
 
 function init(self)
@@ -18,6 +19,7 @@ function init(self)
 		popup_on_popup = self.popup_on_popup,
 		transition_id = self.transition_id,
 		focus_id = self.focus_id,
+		auto_preload = self.preload,
 	}
 	monarch.register_factory(self.screen_id, self.screen_factory, settings)
 end

monarch/screen_proxy.script

@@ -7,6 +7,7 @@ go.property("popup_on_popup", false)
 go.property("timestep_below_popup", 1)
 go.property("transition_url", msg.url())
 go.property("focus_url", msg.url())
+go.property("preload", false)
 
 
 function init(self)
@@ -22,6 +23,7 @@ function init(self)
 		transition_url = self.transition_url ~= url and self.transition_url or nil,
 		focus_url = self.focus_url ~= url and self.focus_url or nil,
 		timestep_below_popup = self.timestep_below_popup,
+		auto_preload = self.preload,
 	}
 
 	monarch.register_proxy(self.screen_id, self.screen_proxy, settings)

test/data/background.collection

@@ -0,0 +1,22 @@
+name: "default"
+scale_along_z: 0
+embedded_instances {
+  id: "go"
+  data: ""
+  position {
+    x: 0.0
+    y: 0.0
+    z: 0.0
+  }
+  rotation {
+    x: 0.0
+    y: 0.0
+    z: 0.0
+    w: 1.0
+  }
+  scale3 {
+    x: 1.0
+    y: 1.0
+    z: 1.0
+  }
+}

test/data/screen_preload.collection

@@ -0,0 +1,37 @@
+name: "screen_preload"
+scale_along_z: 0
+embedded_instances {
+  id: "go"
+  data: "components {\n"
+  "  id: \"screen_preload\"\n"
+  "  component: \"/test/data/screen_preload.gui\"\n"
+  "  position {\n"
+  "    x: 0.0\n"
+  "    y: 0.0\n"
+  "    z: 0.0\n"
+  "  }\n"
+  "  rotation {\n"
+  "    x: 0.0\n"
+  "    y: 0.0\n"
+  "    z: 0.0\n"
+  "    w: 1.0\n"
+  "  }\n"
+  "}\n"
+  ""
+  position {
+    x: 0.0
+    y: 0.0
+    z: 0.0
+  }
+  rotation {
+    x: 0.0
+    y: 0.0
+    z: 0.0
+    w: 1.0
+  }
+  scale3 {
+    x: 1.0
+    y: 1.0
+    z: 1.0
+  }
+}

test/data/screen_preload.gui

@@ -0,0 +1,131 @@
+script: "/test/data/screen_preload.gui_script"
+fonts {
+  name: "example"
+  font: "/assets/example.font"
+}
+background_color {
+  x: 0.0
+  y: 0.0
+  z: 0.0
+  w: 0.0
+}
+nodes {
+  position {
+    x: 320.0
+    y: 697.0
+    z: 0.0
+    w: 1.0
+  }
+  rotation {
+    x: 0.0
+    y: 0.0
+    z: 0.0
+    w: 1.0
+  }
+  scale {
+    x: 1.0
+    y: 1.0
+    z: 1.0
+    w: 1.0
+  }
+  size {
+    x: 200.0
+    y: 100.0
+    z: 0.0
+    w: 1.0
+  }
+  color {
+    x: 1.0
+    y: 1.0
+    z: 1.0
+    w: 1.0
+  }
+  type: TYPE_BOX
+  blend_mode: BLEND_MODE_ALPHA
+  texture: ""
+  id: "box"
+  xanchor: XANCHOR_NONE
+  yanchor: YANCHOR_NONE
+  pivot: PIVOT_CENTER
+  adjust_mode: ADJUST_MODE_FIT
+  layer: ""
+  inherit_alpha: true
+  slice9 {
+    x: 0.0
+    y: 0.0
+    z: 0.0
+    w: 0.0
+  }
+  clipping_mode: CLIPPING_MODE_NONE
+  clipping_visible: true
+  clipping_inverted: false
+  alpha: 1.0
+  template_node_child: false
+  size_mode: SIZE_MODE_AUTO
+}
+nodes {
+  position {
+    x: 0.0
+    y: 0.0
+    z: 0.0
+    w: 1.0
+  }
+  rotation {
+    x: 0.0
+    y: 0.0
+    z: 0.0
+    w: 1.0
+  }
+  scale {
+    x: 1.0
+    y: 1.0
+    z: 1.0
+    w: 1.0
+  }
+  size {
+    x: 200.0
+    y: 100.0
+    z: 0.0
+    w: 1.0
+  }
+  color {
+    x: 0.0
+    y: 0.0
+    z: 0.0
+    w: 1.0
+  }
+  type: TYPE_TEXT
+  blend_mode: BLEND_MODE_ALPHA
+  text: "PRELOAD"
+  font: "example"
+  id: "text"
+  xanchor: XANCHOR_NONE
+  yanchor: YANCHOR_NONE
+  pivot: PIVOT_CENTER
+  outline {
+    x: 1.0
+    y: 1.0
+    z: 1.0
+    w: 1.0
+  }
+  shadow {
+    x: 1.0
+    y: 1.0
+    z: 1.0
+    w: 1.0
+  }
+  adjust_mode: ADJUST_MODE_FIT
+  line_break: false
+  parent: "box"
+  layer: ""
+  inherit_alpha: true
+  alpha: 1.0
+  outline_alpha: 1.0
+  shadow_alpha: 1.0
+  template_node_child: false
+  text_leading: 1.0
+  text_tracking: 0.0
+}
+material: "/builtins/materials/gui.material"
+adjust_reference: ADJUST_REFERENCE_PARENT
+max_nodes: 512

test/data/screen_preload.gui_script

@@ -0,0 +1,5 @@
+function init(self)
+	local monarch = require "monarch.monarch"
+	local data = monarch.data(hash("screen_preload"))
+	data.count = data.count + 1
+end

test/data/screens.collection

@@ -350,3 +350,124 @@ embedded_instances {
     z: 1.0
   }
 }
+embedded_instances {
+  id: "background"
+  data: "components {\n"
+  "  id: \"screen_factory\"\n"
+  "  component: \"/monarch/screen_factory.script\"\n"
+  "  position {\n"
+  "    x: 0.0\n"
+  "    y: 0.0\n"
+  "    z: 0.0\n"
+  "  }\n"
+  "  rotation {\n"
+  "    x: 0.0\n"
+  "    y: 0.0\n"
+  "    z: 0.0\n"
+  "    w: 1.0\n"
+  "  }\n"
+  "  properties {\n"
+  "    id: \"screen_id\"\n"
+  "    value: \"background\"\n"
+  "    type: PROPERTY_TYPE_HASH\n"
+  "  }\n"
+  "}\n"
+  "embedded_components {\n"
+  "  id: \"collectionfactory\"\n"
+  "  type: \"collectionfactory\"\n"
+  "  data: \"prototype: \\\"/test/data/background.collection\\\"\\n"
+  "load_dynamically: false\\n"
+  "\"\n"
+  "  position {\n"
+  "    x: 0.0\n"
+  "    y: 0.0\n"
+  "    z: 0.0\n"
+  "  }\n"
+  "  rotation {\n"
+  "    x: 0.0\n"
+  "    y: 0.0\n"
+  "    z: 0.0\n"
+  "    w: 1.0\n"
+  "  }\n"
+  "}\n"
+  ""
+  position {
+    x: 0.0
+    y: 0.0
+    z: 0.0
+  }
+  rotation {
+    x: 0.0
+    y: 0.0
+    z: 0.0
+    w: 1.0
+  }
+  scale3 {
+    x: 1.0
+    y: 1.0
+    z: 1.0
+  }
+}
+embedded_instances {
+  id: "screen_preload"
+  data: "components {\n"
+  "  id: \"screen\"\n"
+  "  component: \"/monarch/screen_factory.script\"\n"
+  "  position {\n"
+  "    x: 0.0\n"
+  "    y: 0.0\n"
+  "    z: 0.0\n"
+  "  }\n"
+  "  rotation {\n"
+  "    x: 0.0\n"
+  "    y: 0.0\n"
+  "    z: 0.0\n"
+  "    w: 1.0\n"
+  "  }\n"
+  "  properties {\n"
+  "    id: \"screen_id\"\n"
+  "    value: \"screen_preload\"\n"
+  "    type: PROPERTY_TYPE_HASH\n"
+  "  }\n"
+  "  properties {\n"
+  "    id: \"preload\"\n"
+  "    value: \"true\"\n"
+  "    type: PROPERTY_TYPE_BOOLEAN\n"
+  "  }\n"
+  "}\n"
+  "embedded_components {\n"
+  "  id: \"collectionfactory\"\n"
+  "  type: \"collectionfactory\"\n"
+  "  data: \"prototype: \\\"/test/data/screen_preload.collection\\\"\\n"
+  "load_dynamically: false\\n"
+  "\"\n"
+  "  position {\n"
+  "    x: 0.0\n"
+  "    y: 0.0\n"
+  "    z: 0.0\n"
+  "  }\n"
+  "  rotation {\n"
+  "    x: 0.0\n"
+  "    y: 0.0\n"
+  "    z: 0.0\n"
+  "    w: 1.0\n"
+  "  }\n"
+  "}\n"
+  ""
+  position {
+    x: 0.0
+    y: 0.0
+    z: 0.0
+  }
+  rotation {
+    x: 0.0
+    y: 0.0
+    z: 0.0
+    w: 1.0
+  }
+  scale3 {
+    x: 1.0
+    y: 1.0
+    z: 1.0
+  }
+}

test/test_monarch.lua

@@ -6,6 +6,8 @@ local monarch = require "monarch.monarch"
 local SCREEN1_STR = hash("screen1")
 local SCREEN1 = hash(SCREEN1_STR)
 local SCREEN2 = hash("screen2")
+local SCREEN_PRELOAD = hash("screen_preload")
+local BACKGROUND = hash("background")
 local POPUP1 = hash("popup1")
 local POPUP2 = hash("popup2")
 local FOOBAR = hash("foobar")
@@ -16,11 +18,11 @@ return function()
 	local screens_instances = {}
 
 	local function is_shown(screen_id)
-		return monarch.is_top(screen_id)
+		return monarch.is_visible(screen_id)
 	end
 
 	local function is_hidden(screen_id)
-		return not monarch.is_top(screen_id)
+		return not monarch.is_visible(screen_id)
 	end
 
 	local function wait_timeout(fn, ...)
@@ -31,7 +33,10 @@ return function()
 		end)
 		return fn(...)
 	end
-		
+
+	local function wait_until_visible(screen_id)
+		return wait_timeout(is_visible, screen_id)
+	end
 	local function wait_until_shown(screen_id)
 		return wait_timeout(is_shown, screen_id)
 	end
@@ -60,6 +65,7 @@ return function()
 			mock_msg.mock()
 			monarch = require "monarch.monarch"
 			screens_instances = collectionfactory.create("#screensfactory")
+			monarch.debug()
 		end)
 
 		after(function()
@@ -103,6 +109,64 @@ return function()
 			assert_stack({ })
 		end)
 
+		it("should be able to tell if a screen is visible or not", function()
+			assert(not monarch.is_visible(SCREEN1))
+			monarch.show(SCREEN1)
+			assert(wait_until_shown(SCREEN1), "Screen1 was never shown")
+			assert_stack({ SCREEN1 })
+			assert(monarch.is_visible(SCREEN1))
+			
+			monarch.show(SCREEN2)
+			assert(wait_until_hidden(SCREEN1), "Screen1 was never hidden")
+			assert(wait_until_shown(SCREEN2), "Screen2 was never shown")
+			assert_stack({ SCREEN1, SCREEN2 })
+			assert(not monarch.is_visible(SCREEN1))
+			assert(monarch.is_visible(SCREEN2))
+			
+			monarch.show(POPUP1)
+			assert(wait_until_shown(POPUP1), "Popup1 was never shown")
+			assert_stack({ SCREEN1, SCREEN2, POPUP1 })
+			assert(not monarch.is_visible(SCREEN1))
+			assert(monarch.is_visible(SCREEN2))
+			assert(monarch.is_visible(POPUP1))
+		end)
+
+		it("should be able to show a screen without adding it to the stack", function()
+			monarch.show(BACKGROUND, { no_stack = true })
+			assert(wait_until_shown(BACKGROUND), "Background was never shown")
+			assert_stack({ })
+
+			monarch.show(SCREEN1)
+			assert(wait_until_shown(SCREEN1), "Screen1 was never shown")
+			assert_stack({ SCREEN1 })
+		end)
+
+		it("should be able to hide a screen not added to the stack", function()
+			monarch.show(BACKGROUND, { no_stack = true })
+			assert(wait_until_shown(BACKGROUND), "Background was never shown")
+			assert_stack({ })
+
+			monarch.hide(BACKGROUND)
+			assert(wait_until_hidden(BACKGROUND), "Background was never hidden")
+			assert_stack({ })
+		end)
+
+		it("should be able to hide the top screen", function()
+			monarch.show(SCREEN1)
+			assert(wait_until_shown(SCREEN1), "Screen1 was never shown")
+			assert_stack({ SCREEN1 })
+
+			monarch.show(SCREEN2)
+			assert(wait_until_hidden(SCREEN1), "Screen1 was never hidden")
+			assert(wait_until_shown(SCREEN2), "Screen2 was never shown")
+			assert_stack({ SCREEN1, SCREEN2 })
+
+			assert(monarch.hide(SCREEN1) == false)
+			assert(monarch.hide(SCREEN2) == true)
+			assert(wait_until_hidden(SCREEN2), "Screen2 was never hidden")
+			assert(wait_until_shown(SCREEN1), "Screen1 was never shown")
+			assert_stack({ SCREEN1 })
+		end)
 
 		it("should be able to pass data to a screen when showning it or going back to it", function()
 			local data1 = { foo = "bar" }
@@ -147,7 +211,7 @@ return function()
 		end)
 		
 
-		it("should be able to show one popup on top of another the Popup On Popup flag is set", function()
+		it("should be able to show one popup on top of another if the Popup On Popup flag is set", function()
 			monarch.show(SCREEN1)
 			assert(wait_until_shown(SCREEN1), "Screen1 was never shown")
 			assert_stack({ SCREEN1 })
@@ -238,6 +302,14 @@ return function()
 			assert(wait_until_not_busy())
 		end)
 
+		it("should ignore any preload calls while busy", function()
+			monarch.show(TRANSITION1)
+			-- previously a call to preload() while also showing a screen would
+			-- lock up monarch. See issue #32
+			monarch.preload(TRANSITION1)
+			assert(wait_until_shown(TRANSITION1), "Transition1 was never shown")
+		end)
+		
 		it("should be able to notify listeners of navigation events", function()
 			local URL1 = msg.url(screens_instances[hash("/listener1")])
 			local URL2 = msg.url(screens_instances[hash("/listener2")])
@@ -284,5 +356,31 @@ return function()
 			assert(mock_msg.messages(URL1)[10].message_id == monarch.SCREEN_TRANSITION_IN_FINISHED)
 			assert(mock_msg.messages(URL1)[10].message.screen == SCREEN1)
 		end)
+
+
+		it("should be able to preload a screen and always keep it loaded", function()
+			monarch.show(SCREEN_PRELOAD, nil, { count = 1 })
+			assert(wait_until_shown(SCREEN_PRELOAD), "Screen_preload was never shown")
+			-- first time the screen gets loaded it will increment the count
+			assert(monarch.data(SCREEN_PRELOAD).count == 2)
+
+			monarch.show(SCREEN_PRELOAD, { clear = true }, { count = 1 })
+			assert(wait_until_shown(SCREEN_PRELOAD), "Screen_preload was never shown")
+			-- second time the screen gets shown it will already be loaded and not increment the count
+			assert(monarch.data(SCREEN_PRELOAD).count == 1)
+		end)
+
+
+		it("should be able to reload a preloaded screen", function()
+			monarch.show(SCREEN_PRELOAD, nil, { count = 1 })
+			assert(wait_until_shown(SCREEN_PRELOAD), "Screen_preload was never shown")
+			-- first time the screen gets loaded it will increment the count
+			assert(monarch.data(SCREEN_PRELOAD).count == 2)
+
+			monarch.show(SCREEN_PRELOAD, { clear = true, reload = true }, { count = 1 })
+			assert(wait_until_shown(SCREEN_PRELOAD), "Screen_preload was never shown")
+			-- second time the screen gets shown it will be reloaded and increment the count
+			assert(monarch.data(SCREEN_PRELOAD).count == 2)
+		end)
 	end)
 end