I ran into a strange problem recently. I wrote an application class which uses a very simple renderer to draw some models on screen. The camera is movable.
I ran the program on my laptop. Initially I noticed that nothing was being drawn on screen (the screen was being cleared by the correct color, however). Then I noticed that the screen would update itself IF I clicked on the decoration frame and moved the window: this way, the models became visible, but would not move unless I clicked and moved the decoration frame again.
I tested my program on a desktop computer, and everything worked fine; the camera moved smoothly.
Eventually, I got the program to work on my laptop, but I have to set SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 0 );
and disable buffer swapping.
Below is the main application class. In the execution loop, I call the application state stack to loop & render (the application state actually owns the renderer).
In case it is of any consequence, my laptop has intel HD 4000 graphics, and the desktop has a GTX 670.
App::App() : _running( false ),
_deltaTime( 0u ),
_elapsedTime( 0u ),
_mainWindow( nullptr ),
_glContext(),
_stack() {
//ctor
}
App::~App() {
SDL_GL_DeleteContext( _glContext );
SDL_DestroyWindow( _mainWindow );
SDL_Quit();
}
void App::execute() {
_initialize();
static const float millisecondsPerFrame = 17;
while ( _running ) {
//get the delta time & update elapsed time
uint32_t oldTime = _elapsedTime;
_elapsedTime = SDL_GetTicks();
_deltaTime = _elapsedTime - oldTime;
_processEvents();
_loop( _deltaTime / 1000.0f );
_render();
//apply possible state changes made to the stack
_stack.applyPendingChanges();
int usedTime = SDL_GetTicks() - int ( _elapsedTime );
//sleep the remainder of the cycle if we didn't use the entire update cycle
if ( millisecondsPerFrame - usedTime > 0 ) {
SDL_Delay( uint32_t ( millisecondsPerFrame - usedTime ) );
}
}
}
void App::_initialize() {
//initialize random number generator
nge::srand();
_running = true;
_initializeSDL();
_initializeOpenGL();
SDL_GL_MakeCurrent( _mainWindow, _glContext );
//attempt to set late swap tearing
int res = SDL_GL_SetSwapInterval( -1 );
//returns 0 on success
//returns -1 if swap interval is not supported
if ( res == -1 ) {
std::cout << "App::_initializeSDL> " << SDL_GetError() << "\n\n";
SDL_GL_SetSwapInterval( 1 );
}
_stack.registerState<GameState>( AppStateID::Game );
_stack.pushState( AppStateID::Game );
_stack.applyPendingChanges();
}
void App::_initializeSDL() {
SDL_Init( SDL_INIT_VIDEO );
SDL_Init( SDL_INIT_TIMER );
SDL_GL_SetAttribute( SDL_GL_CONTEXT_MAJOR_VERSION, 3 );
SDL_GL_SetAttribute( SDL_GL_CONTEXT_MINOR_VERSION, 3 );
SDL_GL_SetAttribute( SDL_GL_CONTEXT_PROFILE_MASK,
SDL_GL_CONTEXT_PROFILE_CORE );
SDL_GL_SetAttribute( SDL_GL_ACCELERATED_VISUAL, 1 );
/**
For some reason, on my Samsung Series 9, double buffering does not
work.
*/
SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 0 );
SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 16 );
SDL_GL_SetAttribute( SDL_GL_STENCIL_SIZE, 8 );
//anti-aliasing
SDL_GL_SetAttribute( SDL_GL_MULTISAMPLEBUFFERS, 1 );
SDL_GL_SetAttribute( SDL_GL_MULTISAMPLESAMPLES, 4 );
_mainWindow = SDL_CreateWindow( "window",
SDL_WINDOWPOS_UNDEFINED,
SDL_WINDOWPOS_UNDEFINED,
800,
600,
SDL_WINDOW_OPENGL |
SDL_WINDOW_RESIZABLE |
SDL_WINDOW_MAXIMIZED |
SDL_WINDOW_SHOWN );
_glContext = SDL_GL_CreateContext( _mainWindow );
}
void App::_initializeOpenGL() {
//initialize GLEW
glewExperimental = GL_TRUE;
if ( glewInit() != GLEW_OK ) {
std::cerr << "glewInit failed." << std::endl;
std::exit( EXIT_FAILURE );
}
glEnable( GL_DEPTH_TEST );
//enable culling
glEnable( GL_CULL_FACE );
glCullFace( GL_BACK );
glDepthFunc( GL_LEQUAL );
glEnable( GL_TEXTURE_CUBE_MAP_SEAMLESS );
std::cout << "OpenGL version: " << glGetString( GL_VERSION ) << std::endl;
std::cout << "GLSL version: " << glGetString( GL_SHADING_LANGUAGE_VERSION ) << std::endl;
std::cout << "Vendor: " << glGetString( GL_VENDOR ) << std::endl;
std::cout << "Renderer: " << glGetString( GL_RENDERER ) << std::endl << std::endl;
//make sure OpenGL 3.3 is available
ASSERT( GLEW_VERSION_3_3, "OpenGL 3.3 API is not available" );
}
void App::_processEvents() {
SDL_Event event;
while ( SDL_PollEvent( &event ) ) {
if ( event.type == SDL_QUIT ) {
_running = false;
}
}
}
void App::_loop( float delta ) {
_stack.loop( delta );
}
void App::_render() {
_stack.render();
//SDL_GL_SwapWindow( _mainWindow );
}