当我在 C++/SFML 中按下鼠标按钮时如何绘制球

Question

我正在使用 SFML 在 C++ 中做一个游戏，我想在屏幕上绘制一个冰球，然后在按下鼠标左键时在屏幕上看到它 "walking"。但是当我按下按钮时，它并没有画出冰球。你有解决问题的答案吗？

主要：

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

int main(int argc, char* argv[])
{

    sf::RenderWindow window;
    window.create(sf::VideoMode(1320, 840), "Game");
    window.setFramerateLimit(60);
    window.setVerticalSyncEnabled(true);
    sf::Color color(255, 255, 255, 100);

    sf::Time time = sf::seconds(2);
    sf::Clock clock;
    sf::Time time2 = clock.getElapsedTime();

    std::cout << time.asSeconds() << std::endl;
    std::cout << time2.asSeconds() << std::endl;
    //clock.restart();

    //TEXTURE
    sf::Texture bgTexture;
    if (!bgTexture.loadFromFile("file", sf::IntRect(0, 0, 1320, 840)))
    { std::cout << "Error: background not loaded" << std::endl; }

    sf::Texture pTexture;
    if (!pTexture.loadFromFile("file", sf::IntRect(0, 0, 32, 32)))
    { std::cout << "Error: player not loaded" << std::endl; }

    sf::Texture ibTexture;
    if (!ibTexture.loadFromFile("file"))
    { std::cout << "Error: ice-ball not loaded" << std::endl; }

    //SPRITE
    sf::Sprite background;
    background.setTexture(bgTexture);

    sf::Sprite player;
    player.setTexture(pTexture);
    player.setScale(2, 2);
    player.setPosition(628, 388);

    sf::Sprite iceBall;
    iceBall.setTexture(ibTexture);
    iceBall.setScale(1.5, 1.5);

    //FONT
    sf::Font font;
    if (!font.loadFromFile("file"))
    { std::cout << "Error: font not loaded" << std::endl; }

    //TEXT
    sf::Text commands;
    commands.setFont(font);
    commands.setCharacterSize(54);
    commands.setColor(sf::Color::Black);
    commands.setString("D=Right \nA=Left \nW=Up \nS=DWON \n(also the arrows)");
    commands.setPosition(213, 123);

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

            if (event.type == sf::Event::KeyPressed) {
                if (event.key.code == sf::Keyboard::D || event.key.code == sf::Keyboard::Right)
                { player.move(10, 0); }
                else if (event.key.code == sf::Keyboard::A || event.key.code == sf::Keyboard::Left)
                { player.move(-10, 0); }
                else if (event.key.code == sf::Keyboard::W || event.key.code == sf::Keyboard::Up)
                { player.move(0, -10); }
                else if (event.key.code == sf::Keyboard::S || event.key.code == sf::Keyboard::Down)
                { player.move(0, 10); }
            }

            /*if (event.type == sf::Event::MouseMoved)
            {
                std::cout << "X: " << event.mouseMove.x << " y: " << event.mouseMove.y << std::endl;
            }*/

            if (event.type == sf::Event::MouseButtonPressed) {
                if (sf::Mouse::isButtonPressed(sf::Mouse::Left)) {
                    std::cout << "Left mouse button pressed" << std::endl;
                    iceBall.setPosition(event.mouseMove.x, event.mouseMove.y);
                    window.draw(iceBall);
                    iceBall.move(event.mouseMove.x++, event.mouseMove.y++);

                }
            }
        }
        window.clear(color);

        window.draw(background);
        window.draw(player);
        window.draw(commands);

        window.display();
    }

    return 0;
}

Answer 1

让我们看看您的程序的工作流程：

你处理事件，根据左键状态画冰球。
然后，在事件处理之后，您清空屏幕并绘制更多内容。

因此，你永远不会真正展示球。

相反，按如下方式构建您的程序：

while (window.isOpen) {
    sf::Event event;
    while (window.pollEvent(event)) {
        // Handle event & game *logic* here -- not drawing
        // e.g. move entities

        if (event.type == sf::Event::MouseButtonPressed && event.mouseButton.button == sf::Mouse::Left) {
            iceBall.setPosition(event.mouseButton.x, event.mouseButton.y);
            // CAREFUL HERE: you mixed wrong element of the union event.
        }
    }

    // Draw everything here
    window.clear();
    window.draw(background);
    window.draw(player);
    window.draw(iceBall);
    window.draw(command);
    window.display();
}

补充说明：在您的代码中您使用了 event.mouseMove 而 event 的类型不是鼠标移动。这是无效的。查看 tutorial，尤其是这条注释：

Read the above paragraph once again and make sure that you fully understand it, the sf::Event union is the cause of many problems for inexperienced programmers.

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