Naive Center -> Mouse Position Projectile SFML Example

Projectile

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

sf::Vector2f unitVec(const sf::Vector2f& vec);

int main(int argc, char** argv)
{
	sf::RenderWindow window({800, 600}, "Line To Mouse");
	window.setVerticalSyncEnabled(true);

	const sf::Vector2f CENTER = static_cast<sf::Vector2f>(window.getSize() / 2u);
	constexpr float LENGTH = 35.f;
	constexpr float VELOCITY = 122.f;

	sf::VertexArray line(sf::Lines, 2);

	line[0].position = CENTER;
	line[0].color = sf::Color::Red;
	line[1].position = CENTER;
	line[1].color = sf::Color::Red;

	bool shot = false;
	bool update = false;

	sf::Clock clock;

	while(window.isOpen())
	{
		sf::Time dt = clock.restart();

		sf::Event event;
		while(window.pollEvent(event))
		{
			switch(event.type)
			{
				case sf::Event::Closed:
					window.close();
					break;

				case sf::Event::KeyPressed:
					if(event.key.code == sf::Keyboard::Escape)
						window.close();
					break;

				case sf::Event::MouseEntered:
					update = true;
					break;

				case sf::Event::MouseLeft:
					update = false;
					break;

				case sf::Event::MouseButtonReleased:
					if(update)
					{
						sf::Vector2f mousePos = {static_cast<float>(event.mouseButton.x),
												static_cast<float>(event.mouseButton.y)};

						sf::Vector2f projEndNorm = unitVec(mousePos - CENTER);
						line[0].position = CENTER + projEndNorm;	// offset from the center slightly so line[0].position - CENTER will != {0, 0}
						line[1].position = projEndNorm * LENGTH + CENTER;

						shot = true;
					}

				default:
					break;
			}
		}

		if(shot)
		{
			line[0].position += unitVec(line[0].position - CENTER) * VELOCITY * dt.asSeconds();
			line[1].position += unitVec(line[1].position - CENTER) * VELOCITY * dt.asSeconds();

			if(line[0].position.x < 0 || line[0].position.x > 800 && line[0].position.y < 0 || line[0].position.y > 600)
				shot = false;
		}

		window.clear();

		if(shot)
			window.draw(line);

		window.display();
	}

	return 0;
}

sf::Vector2f unitVec(const sf::Vector2f& vec)
{
	if(vec.x != 0 && vec.y != 0)
		return vec / std::sqrt(vec.x * vec.x + vec.y * vec.y);
	else
		return {0, 0};
}