Cannot get smooth movement in SFML - c++

Question

I searched on this topic and found that using sf::Clock to implement frame independent update(using deltaTime) can help to solve it. However even after adding it the paddle movement stutters a bit. On the other hand when I shift the entire Playing case to the event polling loop without using deltatime the game seems to run smoothly.
How do I go about using sf::Clock properly in my code and why does my game seems to run smoothly when I shift the Playing case in event pool loop without even using deltatime?
Game initialization:
void Game::start() {
if (_gameState != Uninitialized) {
return;
}
//Creating window
_mainWindow.create(sf::VideoMode(SCREEN_WIDTH, SCREEN_HEIGHT, 32), "Pong");
_gameState = ShowingMenu;
//Adding game entities to the manager
VisibleGameObject *paddle1 = new PlayerPaddle("Player1", 1.0f, sf::Keyboard::Key::Up, sf::Keyboard::Key::Down);
VisibleGameObject *paddle2 = new PlayerPaddle("Player2", 1.0f, sf::Keyboard::Key::W, sf::Keyboard::Key::S);
VisibleGameObject *background = new Background("Background", 0.0f);
paddle1 -> setPosition(SCREEN_WIDTH - (paddle1 -> getWidth()), 0);
paddle2->setPosition(0, 0);
manager.addObject(paddle1);
manager.addObject(paddle2);
manager.addObject(background);
//Starting Clock
deltaTime = 0.0f;
frameClock.restart();
while (!isExiting()) {
gameLoop();
}
_mainWindow.close();
}
Game Loop :
void Game::gameLoop()
{
static bool firstPass = true;
sf::Event currentEvent;
//Event loop
while(_mainWindow.pollEvent(currentEvent) || firstPass)
{
if (firstPass) {
currentEvent = sf::Event();
currentEvent.type = sf::Event::GainedFocus;
firstPass = false;
}
if (currentEvent.type == sf::Event::Closed)
{
_gameState = Exiting;
}
switch (_gameState)
{
case ShowingMenu:
{
showingMenu();
break;
}
case Paused:
{
break;
}
default:
break;
}
}
//Extracting deltaTime to update game logic
deltaTime = frameClock.restart().asSeconds();
if(_gameState == Playing)
{
manager.updateAllLayers(deltaTime);
manager.drawAllLayers(_mainWindow);
_mainWindow.display();
}
}
Paddle Update Logic:
void PlayerPaddle::update(const float & elapsedTime)
{
sf::Vector2f currentPos = getPosition();
float displacement = 0.0f;
if (sf::Keyboard::isKeyPressed(controls.up))
{
displacement = -speed * elapsedTime;
}
else if (sf::Keyboard::isKeyPressed(controls.down))
{
displacement = speed * elapsedTime;
}
if (displacement + currentPos.y < 0.0f)
{
setPosition(currentPos.x, 0.0f);
return;
}
else if (displacement + currentPos.y + getHeight() > Game::SCREEN_HEIGHT)
{
setPosition(currentPos.x, Game::SCREEN_HEIGHT - getHeight());
return;
}
setPosition(currentPos.x, currentPos.y + displacement);
}

Answer 1

I don't have enough reputation to post a comment so I'll have to make this an answer...
You update (and draw) every frame. Your game loop doesn't make sense if you want to implement a fixed update time step.
This is how your game loop should look like. I use your variable names for your convenience:
// ...
sf::Clock frameClock;
const sf::Time timePerFrame = sf::seconds(1.0f / 60.0f);
sf::Time timeSinceLastUpdate = sf::Time::Zero;
while (_mainWindow.isOpen()) {
timeSinceLastUpdate += frameClock.restart();
// events
{
sf::Event evt;
while (_mainWindow.pollEvent(evt)) {
//...
}
}
// update
{
while (timeSinceLastUpdate > timePerFrame) {
timeSinceLastUpdate -= timePerFrame;
manager.updateAllLayers(timePerFrame);
}
}
// render
{
_mainWindow.clear();
// ...
_mainWindow.display();
}
}
// ...
This updates your game at a fixed rate (1/60s) and renders it whenever possible (you can use setFramerateLimit() to limit the FPS; this won't affect the fixed update interval, so no problem there).
You now pass sf::Time to your manager.updateAllLayers which is used like your elapsedTime (it has functions like .asSeconds() so essentially nothing changes but you'll obviously have to adjust the values for speed)