bezier_curve.cpp

#include <SFML/Graphics.hpp>
// #define CATCH_CONFIG_MAIN
// #include <catch.hpp>

void draw_lines(const std::vector<sf::Vector2f>& vector, sf::RenderWindow& window, sf::Color color = sf::Color::White)
{
	for (auto it{vector.cbegin()}; it != vector.cend();)
	{
		auto current_it{it};
		if (++it != vector.cend())
		{
			sf::Vertex line[2]
			{
				{*current_it, color},
				{*it, color}
			};

			window.draw(line, 2, sf::Lines);
		}
	}
}

float interpolate(float t, float a, float b)
{
	return (b - a) * t + a;
}

sf::Vector2f vinterpolate(float t, sf::Vector2f a, sf::Vector2f b)
{
	return {interpolate(t, a.x, b.x), interpolate(t, a.y, b.y)};
}

// TEST_CASE("Interpolation")
// {
// 	CHECK(interpolate(.1f, 0, 100) == 10);
// 	CHECK(interpolate(.1f, 0, 200) == 20);
// 	CHECK(interpolate(.1f, 100, 200) == 110);
// }

int main()
{
	sf::RenderWindow window({350, 350}, "SFML", sf::Style::Default, sf::ContextSettings{0, 0, 8});

	std::vector<sf::Vector2f> points;

	while (true)
	{
		sf::Event event;
		while (window.pollEvent(event))
		{
			if (event.type == sf::Event::Closed || (event.type == sf::Event::KeyPressed && event.key.code == sf::Keyboard::Escape))
				return 0;

			if (event.type == sf::Event::MouseButtonPressed)
				points.emplace_back(event.mouseButton.x, event.mouseButton.y);
		}

		std::vector<sf::Vector2f> curve;
		for (float n{50}, t{0}; t <= 1.01; t += 1 / n)
		{
			std::vector<sf::Vector2f> remaining_points{points};

			while (remaining_points.size() > 1)
			{
				std::vector<sf::Vector2f> current_remaining_points;
				for (auto it{remaining_points.cbegin()}; it != remaining_points.cend();)
				{
					auto current_it{it};
					if (++it != remaining_points.cend())
						current_remaining_points.push_back(vinterpolate(t, *current_it, *it));
				}
				remaining_points = current_remaining_points;
			}

			if (!remaining_points.empty())
				curve.push_back(remaining_points[0]);
		}

		window.clear();
		draw_lines(points, window, {100, 100, 100});
		draw_lines(curve, window);
		window.display();
	}   
}