Platform: make it possible to run main loop iterations manually.

src/Magnum/Platform/Sdl2Application.cpp

@@ -319,10 +319,10 @@ Sdl2Application::~Sdl2Application() {
 
 int Sdl2Application::exec() {
     #ifndef CORRADE_TARGET_EMSCRIPTEN
-    while(!(_flags & Flag::Exit)) mainLoop();
+    while(!(_flags & Flag::Exit)) mainLoopIteration();
     #else
     emscripten_set_main_loop_arg([](void* arg) {
-        static_cast<Sdl2Application*>(arg)->mainLoop();
+        static_cast<Sdl2Application*>(arg)->mainLoopIteration();
     }, this, 0, true);
     #endif
     return 0;
@@ -336,7 +336,7 @@ void Sdl2Application::exit() {
     #endif
 }
 
-void Sdl2Application::mainLoop() {
+void Sdl2Application::mainLoopIteration() {
     #ifndef CORRADE_TARGET_EMSCRIPTEN
     const UnsignedInt timeBefore = _minimalLoopPeriod ? SDL_GetTicks() : 0;
     #endif

src/Magnum/Platform/Sdl2Application.h

@@ -389,13 +389,29 @@ class Sdl2Application {
          * @brief Execute main loop
          * @return Value for returning from `main()`
          *
-         * See @ref MAGNUM_SDL2APPLICATION_MAIN() for usage information.
+         * Calls @ref mainLoopIteration() in a loop until @ref exit() is
+         * called. See @ref MAGNUM_SDL2APPLICATION_MAIN() for usage
+         * information.
          */
         int exec();
 
-        /** @brief Exit application main loop */
+        /**
+         * @brief Exit application main loop
+         *
+         * Stops main loop started by @ref exec().
+         */
         void exit();
 
+        /**
+         * @brief Run one iteration of application main loop
+         *
+         * Called internally from @ref exec(). If you want to have better
+         * control over how the main loop behaves, you can call this function
+         * yourself from your own `main()` function instead of it being called
+         * automatically from @ref exec() / @ref MAGNUM_SDL2APPLICATION_MAIN().
+         */
+        void mainLoopIteration();
+
         #ifndef CORRADE_TARGET_EMSCRIPTEN
         /**
          * @brief Underlying window handle
@@ -710,8 +726,6 @@ class Sdl2Application {
         typedef Containers::EnumSet<Flag> Flags;
         CORRADE_ENUMSET_FRIEND_OPERATORS(Flags)
 
-        void mainLoop();
-
         #ifndef CORRADE_TARGET_EMSCRIPTEN
         SDL_Window* _window;
         SDL_GLContext _glContext;