Platform: implement Sdl2Application::windowSize() on Emscripten.

src/Magnum/Platform/Sdl2Application.cpp

@@ -268,13 +268,15 @@ bool Sdl2Application::tryCreateContext(const Configuration& configuration) {
     return true;
 }
 
-#ifndef CORRADE_TARGET_EMSCRIPTEN
 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
 }
-#endif
 
 void Sdl2Application::swapBuffers() {
     #ifndef CORRADE_TARGET_EMSCRIPTEN

src/Magnum/Platform/Sdl2Application.h

@@ -458,17 +458,14 @@ class Sdl2Application {
 
         /** @{ @name Screen handling */
 
-        #ifndef CORRADE_TARGET_EMSCRIPTEN
         /**
          * @brief Window size
          *
          * Window size to which all input event coordinates can be related.
          * Note that especially on HiDPI systems the reported window size might
          * not be the same as framebuffer size.
-         * @note Not available in @ref CORRADE_TARGET_EMSCRIPTEN "Emscripten".
          */
         Vector2i windowSize();
-        #endif
 
         /**
          * @brief Swap buffers