Platform: provide range-based-for access to application screens.

Similar reasoning as in previous commit for deprecation of frontScreen()
etc.

src/Magnum/Platform/ScreenedApplication.h

@@ -62,15 +62,21 @@ application gets an event, they are propagated to the screens:
     @ref BasicScreen::PropagatedEvent::Input enabled. If any screen sets the
     event as accepted, it is not propagated further.
 
-Traversing through the list of screens is done like following:
+Uses @ref Corrade::Containers::LinkedList for efficient screen management.
+Traversing front-to-back through the list of screens can be done using
+range-based for:
 @code
-// front-to-back
+MyApplication app;
-for(Screen* s = app.frontScreen(); s; s = s->nextFartherScreen()) {
+for(Screen& screen: app.screens()) {
     // ...
 }
+@endcode
 
-// back-to-front
+Or, if you need more flexibility, like in the following code. Traversing
-for(Screen* s = app.backScreen(); s; s = s->nextNearerScreen()) {
+back-to-front can be done using @ref Corrade::Containers::LinkedList::last()
+and @ref BasicScreen::nextNearerScreen().
+@code
+for(Screen* s = app.screens().first(); s; s = s->nextFartherScreen()) {
     // ...
 }
 @endcode
@@ -148,30 +154,46 @@ template<class Application> class BasicScreenedApplication: public Application,
         BasicScreenedApplication<Application>& focusScreen(BasicScreen<Application>& screen);
 
         /**
-         * @brief Front screen
+         * @brief Application screens
          *
-         * @see @ref BasicScreen::nextFartherScreen(), @ref BasicScreen::nextNearerScreen()
+         * The screens are sorted front-to-back.
+         * @see @ref BasicScreen::application(),
+         *      @ref BasicScreen::nextFartherScreen(),
+         *      @ref BasicScreen::nextNearerScreen()
          */
-        BasicScreen<Application>* frontScreen() {
+        Containers::LinkedList<BasicScreen<Application>>& screens() {
-            return Containers::LinkedList<BasicScreen<Application>>::first();
+            return static_cast<Containers::LinkedList<BasicScreen<Application>>&>(*this);
         }
+
         /** @overload */
-        const BasicScreen<Application>* frontScreen() const {
+        const Containers::LinkedList<BasicScreen<Application>>& screens() const {
-            return Containers::LinkedList<BasicScreen<Application>>::first();
+            return static_cast<const Containers::LinkedList<BasicScreen<Application>>&>(*this);
         }
 
+        #ifdef MAGNUM_BUILD_DEPRECATED
+        /**
+         * @brief Front screen
+         * @deprecated Use `screens().first()` instead.
+         */
+        CORRADE_DEPRECATED("use screens().first() instead") BasicScreen<Application>* frontScreen() { return screens().first(); }
+
+        /** @overload
+         * @deprecated Use `screens().first()` instead.
+         */
+        CORRADE_DEPRECATED("use screens().first() instead") const BasicScreen<Application>* frontScreen() const { return screens().first(); }
+
         /**
          * @brief Back screen
-         *
+         * @deprecated Use `screens().last()` instead.
-         * @see @ref BasicScreen::nextFartherScreen(), @ref BasicScreen::nextNearerScreen()
          */
-        BasicScreen<Application>* backScreen() {
+        CORRADE_DEPRECATED("use screens().back() instead") BasicScreen<Application>* backScreen() { return screens().last(); }
-            return Containers::LinkedList<BasicScreen<Application>>::last();
+
-        }
+        /**
-        /** @overload */
+         * @overload
-        const BasicScreen<Application>* backScreen() const {
+         * @deprecated Use `screens().last()` instead.
-            return Containers::LinkedList<BasicScreen<Application>>::last();
+         */
-        }
+        CORRADE_DEPRECATED("use screens().back() instead") const BasicScreen<Application>* backScreen() const { return screens().last(); }
+        #endif
 
     protected:
         /* Nobody will need to have (and delete) ScreenedApplication*, thus

src/Magnum/Platform/ScreenedApplication.hpp

@@ -49,7 +49,7 @@ template<class Application> BasicScreenedApplication<Application>::~BasicScreene
 
 template<class Application> BasicScreenedApplication<Application>& BasicScreenedApplication<Application>::addScreen(BasicScreen<Application>& screen) {
     Containers::LinkedList<BasicScreen<Application>>::insert(&screen);
-    if(frontScreen() == &screen) screen.focusEvent();
+    if(screens().first() == &screen) screen.focusEvent();
     Application::redraw();
     return *this;
 }
@@ -63,10 +63,10 @@ template<class Application> BasicScreenedApplication<Application>& BasicScreened
 
 template<class Application> BasicScreenedApplication<Application>& BasicScreenedApplication<Application>::focusScreen(BasicScreen<Application>& screen) {
     /* Already focused, nothing to do */
-    if(frontScreen() == &screen) return *this;
+    if(screens().first() == &screen) return *this;
 
-    frontScreen()->blurEvent();
+    screens().first()->blurEvent();
-    Containers::LinkedList<BasicScreen<Application>>::move(&screen, frontScreen());
+    Containers::LinkedList<BasicScreen<Application>>::move(&screen, screens().first());
     screen.focusEvent();
     Application::redraw();
     return *this;
@@ -78,13 +78,12 @@ template<class Application> void BasicScreenedApplication<Application>::viewport
     /* Call viewport event after all other (because of framebuffer resizing) */
     globalViewportEvent(size);
 
-    for(BasicScreen<Application>* s = Containers::LinkedList<BasicScreen<Application>>::first(); s; s = s->next())
+    for(BasicScreen<Application>& s: *this) s.viewportEvent(size);
-        s->viewportEvent(size);
 }
 
 template<class Application> void BasicScreenedApplication<Application>::drawEvent() {
     /* Back-to-front rendering */
-    for(BasicScreen<Application>* s = backScreen(); s; s = s->nextNearerScreen())
+    for(BasicScreen<Application>* s = screens().last(); s; s = s->nextNearerScreen())
         if(s->propagatedEvents() & Implementation::PropagatedScreenEvent::Draw) s->drawEvent();
 
     /* Call global event after all other (because of buffer swapping) */
@@ -93,7 +92,7 @@ template<class Application> void BasicScreenedApplication<Application>::drawEven
 
 template<class Application> void BasicScreenedApplication<Application>::keyPressEvent(typename Application::KeyEvent& event) {
     /* Front-to-back event propagation, stop when the event gets accepted */
-    for(BasicScreen<Application>* s = frontScreen(); s; s = s->nextFartherScreen()) {
+    for(BasicScreen<Application>* s = screens().first(); s; s = s->nextFartherScreen()) {
         if(s->propagatedEvents() & Implementation::PropagatedScreenEvent::Input) {
             s->keyPressEvent(event);
             if(event.isAccepted()) break;
@@ -103,7 +102,7 @@ template<class Application> void BasicScreenedApplication<Application>::keyPress
 
 template<class Application> void BasicScreenedApplication<Application>::keyReleaseEvent(typename Application::KeyEvent& event) {
     /* Front-to-back event propagation, stop when the event gets accepted */
-    for(BasicScreen<Application>* s = frontScreen(); s; s = s->nextFartherScreen()) {
+    for(BasicScreen<Application>* s = screens().first(); s; s = s->nextFartherScreen()) {
         if(s->propagatedEvents() & Implementation::PropagatedScreenEvent::Input) {
             s->keyReleaseEvent(event);
             if(event.isAccepted()) break;
@@ -113,7 +112,7 @@ template<class Application> void BasicScreenedApplication<Application>::keyRelea
 
 template<class Application> void BasicScreenedApplication<Application>::mousePressEvent(typename Application::MouseEvent& event) {
     /* Front-to-back event propagation, stop when the event gets accepted */
-    for(BasicScreen<Application>* s = frontScreen(); s; s = s->nextFartherScreen()) {
+    for(BasicScreen<Application>* s = screens().first(); s; s = s->nextFartherScreen()) {
         if(s->propagatedEvents() & Implementation::PropagatedScreenEvent::Input) {
             s->mousePressEvent(event);
             if(event.isAccepted()) break;
@@ -123,7 +122,7 @@ template<class Application> void BasicScreenedApplication<Application>::mousePre
 
 template<class Application> void BasicScreenedApplication<Application>::mouseReleaseEvent(typename Application::MouseEvent& event) {
     /* Front-to-back event propagation, stop when the event gets accepted */
-    for(BasicScreen<Application>* s = frontScreen(); s; s = s->nextFartherScreen()) {
+    for(BasicScreen<Application>* s = screens().first(); s; s = s->nextFartherScreen()) {
         if(s->propagatedEvents() & Implementation::PropagatedScreenEvent::Input) {
             s->mouseReleaseEvent(event);
             if(event.isAccepted()) break;
@@ -133,7 +132,7 @@ template<class Application> void BasicScreenedApplication<Application>::mouseRel
 
 template<class Application> void BasicScreenedApplication<Application>::mouseMoveEvent(typename Application::MouseMoveEvent& event) {
     /* Front-to-back event propagation, stop when the event gets accepted */
-    for(BasicScreen<Application>* s = frontScreen(); s; s = s->nextFartherScreen()) {
+    for(BasicScreen<Application>* s = screens().first(); s; s = s->nextFartherScreen()) {
         if(s->propagatedEvents() & Implementation::PropagatedScreenEvent::Input) {
             s->mouseMoveEvent(event);
             if(event.isAccepted()) break;