Revert "Platform: Move emscripten port of Sdl2Application to SDL2"

Size of all executables got inflated by *half a megabyte* because of
this. I'm not sure if the change is worth it, so reverting for now.

This reverts commits

    c01961ba6b
    5fb3f435dd
    fada6fba05

modules/FindMagnum.cmake

@@ -534,10 +534,6 @@ foreach(_component ${Magnum_FIND_COMPONENTS})
                 find_package(SDL2)
                 set_property(TARGET Magnum::${_component} APPEND PROPERTY
                     INTERFACE_LINK_LIBRARIES SDL2::SDL2)
-                if(CORRADE_TARGET_EMSCRIPTEN)
-                    # TODO: give me INTERFACE_LINK_OPTIONS or something, please
-                    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -s USE_SDL=2")
-                endif()
 
             # (Windowless) GLX application dependencies
             elseif(_component STREQUAL GlxApplication OR _component STREQUAL WindowlessGlxApplication)

src/Magnum/Platform/Sdl2Application.cpp

@@ -100,6 +100,7 @@ bool Sdl2Application::tryCreateContext(const Configuration& configuration) {
     SDL_GL_SetAttribute(SDL_GL_FRAMEBUFFER_SRGB_CAPABLE, configuration.isSRGBCapable());
     #endif
 
+    /** @todo Remove when Emscripten has proper SDL2 support */
     #ifndef CORRADE_TARGET_EMSCRIPTEN
     /* Set context version, if user-specified */
     if(configuration.version() != Version::None) {
@@ -146,7 +147,6 @@ bool Sdl2Application::tryCreateContext(const Configuration& configuration) {
         SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_ES);
         #endif
     }
-    #endif
 
     /* Create window. Hide it by default so we don't have distracting window
        blinking in case we have to destroy it again right away */
@@ -238,12 +238,23 @@ bool Sdl2Application::tryCreateContext(const Configuration& configuration) {
     SDL_GL_GetDrawableSize(_window, &drawableSize.x(), &drawableSize.y());
     glViewport(0, 0, drawableSize.x(), drawableSize.y());
     #endif
+    #else
+    /* Emscripten-specific initialization */
+    if(!(_glContext = SDL_SetVideoMode(configuration.size().x(), configuration.size().y(), 24, SDL_OPENGL|SDL_HWSURFACE|SDL_DOUBLEBUF))) {
+        Error() << "Platform::Sdl2Application::tryCreateContext(): cannot create context:" << SDL_GetError();
+        return false;
+    }
+    #endif
 
     /* Destroy everything also when the Magnum context creation fails */
     if(!_context->tryCreate()) {
+        #ifndef CORRADE_TARGET_EMSCRIPTEN
         SDL_GL_DeleteContext(_glContext);
         SDL_DestroyWindow(_window);
         _window = nullptr;
+        #else
+        SDL_FreeSurface(_glContext);
+        #endif
         return false;
     }
 
@@ -258,13 +269,21 @@ bool Sdl2Application::tryCreateContext(const Configuration& configuration) {
 }
 
 Vector2i Sdl2Application::windowSize() {
+    #ifndef CORRADE_TARGET_EMSCRIPTEN
     Vector2i size;
     SDL_GetWindowSize(_window, &size.x(), &size.y());
     return size;
+    #else
+    return {_glContext->w, _glContext->h};
+    #endif
 }
 
 void Sdl2Application::swapBuffers() {
+    #ifndef CORRADE_TARGET_EMSCRIPTEN
     SDL_GL_SwapWindow(_window);
+    #else
+    SDL_Flip(_glContext);
+    #endif
 }
 
 Int Sdl2Application::swapInterval() const {
@@ -291,8 +310,12 @@ bool Sdl2Application::setSwapInterval(const Int interval) {
 Sdl2Application::~Sdl2Application() {
     _context.reset();
 
+    #ifndef CORRADE_TARGET_EMSCRIPTEN
     SDL_GL_DeleteContext(_glContext);
     SDL_DestroyWindow(_window);
+    #else
+    SDL_FreeSurface(_glContext);
+    #endif
     SDL_Quit();
 }
 
@@ -503,7 +526,7 @@ void Sdl2Application::textInputEvent(TextInputEvent&) {}
 void Sdl2Application::textEditingEvent(TextEditingEvent&) {}
 
 Sdl2Application::Configuration::Configuration():
-    #ifndef CORRADE_TARGET_IOS
+    #if !defined(CORRADE_TARGET_EMSCRIPTEN) && !defined(CORRADE_TARGET_IOS)
     _title("Magnum SDL2 Application"),
     #endif
     #ifdef CORRADE_TARGET_EMSCRIPTEN

src/Magnum/Platform/Sdl2Application.h

@@ -227,10 +227,6 @@ file contains event listeners which print loading status on the page. The
 status displayed in the remaining two `<div>`s, if they are available.
 The CSS file contains rudimentary style to avoid eye bleeding.
 
-The document `<title>` can be overriden by calling
-@ref Configuration::setTitle(), but that of course happens only after the app
-fully loads.
-
 The application redirects all output (thus also @ref Corrade::Utility::Debug "Debug",
 @ref Corrade::Utility::Warning "Warning" and @ref Corrade::Utility::Error "Error")
 to JavaScript console. It's possible to pass command-line arguments to `main()`
@@ -419,6 +415,7 @@ class Sdl2Application {
          */
         void mainLoopIteration();
 
+        #ifndef CORRADE_TARGET_EMSCRIPTEN
         /**
          * @brief Underlying window handle
          *
@@ -426,6 +423,7 @@ class Sdl2Application {
          * @note Not available in @ref CORRADE_TARGET_EMSCRIPTEN "Emscripten".
          */
         SDL_Window* window() { return _window; }
+        #endif
 
     protected:
         /* Nobody will need to have (and delete) Sdl2Application*, thus this is
@@ -728,10 +726,12 @@ class Sdl2Application {
         typedef Containers::EnumSet<Flag> Flags;
         CORRADE_ENUMSET_FRIEND_OPERATORS(Flags)
 
+        #ifndef CORRADE_TARGET_EMSCRIPTEN
         SDL_Window* _window;
         SDL_GLContext _glContext;
-        #ifndef CORRADE_TARGET_EMSCRIPTEN
         UnsignedInt _minimalLoopPeriod;
+        #else
+        SDL_Surface* _glContext;
         #endif
 
         std::unique_ptr<Platform::Context> _context;
@@ -830,11 +830,12 @@ class Sdl2Application::Configuration {
         /*implicit*/ Configuration();
         ~Configuration();
 
-        #ifndef CORRADE_TARGET_IOS
+        #if !defined(CORRADE_TARGET_EMSCRIPTEN) && !defined(CORRADE_TARGET_IOS)
         /**
          * @brief Window title
          *
-         * @note Not available in @ref CORRADE_TARGET_IOS "iOS".
+         * @note Not available in @ref CORRADE_TARGET_EMSCRIPTEN "Emscripten"
+         *      and @ref CORRADE_TARGET_IOS "iOS".
          */
         std::string title() const { return _title; }
         #endif
@@ -844,13 +845,12 @@ class Sdl2Application::Configuration {
          * @return Reference to self (for method chaining)
          *
          * Default is `"Magnum SDL2 Application"`.
-         * @note In @ref CORRADE_TARGET_IOS "iOS" this function does nothing and
+         * @note In @ref CORRADE_TARGET_EMSCRIPTEN "Emscripten" and
-         *      is included only for compatibility. You need to set the title
+         *      @ref CORRADE_TARGET_IOS "iOS" this function does nothing and is
+         *      included only for compatibility. You need to set the title
          *      separately in platform-specific configuration file.
-         *      In @ref CORRADE_TARGET_EMSCRIPTEN "Emscripten" this title will
-         *      be used to set `document.title`.
          */
-        #ifndef CORRADE_TARGET_IOS
+        #if !defined(CORRADE_TARGET_EMSCRIPTEN) && !defined(CORRADE_TARGET_IOS)
         Configuration& setTitle(std::string title) {
             _title = std::move(title);
             return *this;
@@ -975,7 +975,7 @@ class Sdl2Application::Configuration {
         #endif
 
     private:
-        #ifndef CORRADE_TARGET_IOS
+        #if !defined(CORRADE_TARGET_EMSCRIPTEN) && !defined(CORRADE_TARGET_IOS)
         std::string _title;
         #endif
         Vector2i _size;