test_jerk.cpp

#include <SFML/Graphics.hpp>
#include <cmath>

// Program parameters.
const float TICK_PER_SEC = 60.f;
const float MAX_JERK_LENGTH = 100.f;

// Computed constants.
const sf::Time TICK_TIME = sf::seconds(1.f / TICK_PER_SEC);

class Player
{
  public:
    explicit Player()
      : position {0.f, 0.f}
      , velocity {0.f, 0.f}
      , acceleration {0.f, 0.f}
      , jerk {0.f, 0.f} 
    {
      shape.setFillColor(sf::Color::Red);
      shape.setSize({20.f, 20.f});
    } 

    void update(const sf::Time &dt)
    {
      // Reset jerk.
      jerk = {0.f, 0.f};

      // Reset player ?
      if (sf::Keyboard::isKeyPressed(sf::Keyboard::Space))
      {
        position = velocity = acceleration = {0.f, 0.f}; 
      }

      // Input reading.
      if (sf::Keyboard::isKeyPressed(sf::Keyboard::Right))
      {
        jerk.x += 1.f;
      }
      else if (sf::Keyboard::isKeyPressed(sf::Keyboard::Left))
      {
        jerk.x -= 1.f;
      }

      if (sf::Keyboard::isKeyPressed(sf::Keyboard::Up))
      {
        jerk.y -= 1.f;
      }
      else if (sf::Keyboard::isKeyPressed(sf::Keyboard::Down))
      {
        jerk.y += 1.f;
      }

      // Normalize jerk and multiply by max jerk length.
      float jerkLength = std::sqrt(std::pow(jerk.x, 2.f) + std::pow(jerk.y, 2.f));
      if (std::fabs(jerkLength) > std::numeric_limits<float>::epsilon())
      {
        jerk *= MAX_JERK_LENGTH / jerkLength;
      }

      // Integration.
      acceleration += jerk * dt.asSeconds();
      velocity += acceleration * dt.asSeconds();
      position += velocity * dt.asSeconds();

      // Update shape.
      shape.setPosition(position);
    }

    void render(sf::RenderWindow &window) const
    {
      window.draw(shape);
    }

  private:
    sf::Vector2f position, velocity, acceleration, jerk;
    sf::RectangleShape shape;
};

int main()
{
  sf::RenderWindow window {sf::VideoMode {1280, 720}, "Jerk"};
  auto view = window.getView();
  view.setCenter(0, 0);
  window.setView(view);

  Player player;

  sf::Clock clock;
  sf::Time elapsed {sf::Time::Zero};
  while (window.isOpen())
  {
    elapsed += clock.restart();

    sf::Event event;
    while (window.pollEvent(event))
    { 
      if (event.type == sf::Event::Closed)
        window.close();
    }

    if (elapsed >= TICK_TIME)
    {
      elapsed -= TICK_TIME;
      player.update(TICK_TIME);
    }

    window.clear();
    player.render(window);
    window.display();
  }

  return 0;
}