// SDL2_03 [OpenGL Window].nova
// Minimal OpenGL ES window, just displaying a background colour.



// Using namespace declarations.
using library.emscripten;
using library.opengl;
using library.sdl2;



// The application class.
class SDL2_03_OpenGL_Window
{
   // Static data members.
   private static SDL_Window w;
   private static SDL_Renderer r;
   private static SDL_GLContext c;


   // Application class's "main" function.
   public static void main( String[] args )
   {
      Stream.writeLine( "SDL2_03 [OpenGL Window].nova" );


      // Disable the emscripten full-screen controls.
      Emscripten.disableControls( );

      // Setup SDL.
      SDL2.SDL_Init( SDL2.SDL_INIT_VIDEO );

      SDL2.SDL_GL_SetAttribute( SDL2.SDL_GL_CONTEXT_MAJOR_VERSION, 2 );
      SDL2.SDL_GL_SetAttribute( SDL2.SDL_GL_CONTEXT_MINOR_VERSION, 0 );
      SDL2.SDL_GL_SetAttribute( SDL2.SDL_GL_DOUBLEBUFFER, 1 );
      SDL2.SDL_GL_SetAttribute( SDL2.SDL_GL_DEPTH_SIZE, 24 );


      w = SDL2.SDL_CreateWindow( "SDL2_03_OpenGLWindow",
                                 SDL2.SDL_WINDOWPOS_CENTERED,
                                 SDL2.SDL_WINDOWPOS_CENTERED,
                                 640,
                                 480,
                                 SDL2.SDL_WINDOW_OPENGL | SDL2.SDL_WINDOW_RESIZABLE );

      // Check for a null reference.
      if ( w == null )
      {
         // Output an error message.
         Stream.writeLine( "Failed to create window: " + SDL2.SDL_GetError( ) );

         // Abort the application.
         return;
      }

      r = SDL2.SDL_CreateRenderer( w,
                                   -1,
                                   SDL2.SDL_RENDERER_ACCELERATED | SDL2.SDL_RENDERER_PRESENTVSYNC );

      c = SDL2.SDL_GL_CreateContext( w );

      // Set the background colour.
      OpenGL.glClearColor( 0.0f, 0.5f, 0.5f, 1.0f );


      // Check for the emscripten environment.
      if ( Emscripten.isActive( ) )
      {
         int simulate_infinite_loop = 1;  // Call the function repeatedly.
         int fps = -1;  // Call the function as fast as the browser wants to render (typically 60fps).
         Emscripten.setMainLoop( renderFrame, fps, simulate_infinite_loop );
      }
      else
      {
         // Rendering and event processing loop.
         do
         {
            SDL_Event e = SDL2.SDL_PollEvent( );
            if ( e != null )
               if ( e.id == SDL2.SDL_QUIT )
                  break;

            renderFrame( );
         }
         while( true );
      }


      // Shutdown app.
      SDL2.SDL_GL_DeleteContext( c );
      SDL2.SDL_DestroyRenderer( r );
      SDL2.SDL_DestroyWindow( w );
      SDL2.SDL_Quit( );
   }


   public static void renderFrame( )
   {
      OpenGL.glClear( OpenGL.GL_COLOR_BUFFER_BIT );

      SDL2.SDL_GL_SwapWindow( w );
   }
}