问当一个角色在屏幕上移动时，window.clear()在SFML中是如何工作的？

EN

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

int main() {
    sf::RenderWindow window(sf::VideoMode(1920, 1080), "Screen", sf::Style::Default);
    sf::RectangleShape player(sf::Vector2f(100.0f, 100.0f));
    player.setFillColor(sf::Color::Green);

    //run as long as the window is open
    while (window.isOpen()) {
        // check all the window's events that were triggered since the last iteration of the loop
        sf::Event evnt;
        while (window.pollEvent(evnt)) {
            switch (evnt.type) {
            case sf::Event::Closed:
                window.close();
                break;
            case sf::Event::Resized:
                printf("New window width: %i New window height: %i\n", evnt.size.width, evnt.size.height);
                break;
            case sf::Event::TextEntered:
                if (evnt.text.unicode < 128) {
                    printf("%c", evnt.text.unicode);
                }
            }
            // "close requested" event: we close the window
            if (evnt.type == sf::Event::Closed)
                window.close();
        }
        if (sf::Keyboard::isKeyPressed(sf::Keyboard::Key::W)){
            player.move(0.0f, -0.1f);
        }
        if (sf::Keyboard::isKeyPressed(sf::Keyboard::Key::A)) {
            player.move(-0.1f, 0.0f);
        }
        if (sf::Keyboard::isKeyPressed(sf::Keyboard::Key::S)) {
            player.move(0.0f, 0.1f);
        }
        if (sf::Keyboard::isKeyPressed(sf::Keyboard::Key::D)) {
            player.move(0.1f, 0.0f);
        }
        window.clear();
        window.draw(player);
        window.display();
    }
    return 0;
}