在SFML中使用精灵不显示图像

Question

我已经在Linux Mint 18.1上使用C ++ 17学习了SFML 2.3.2来学习使用GUI。作为继Hello World之后的第二个项目，我正在尝试重现Snake，那个游戏旧手机已预先安装。大多数东西到现在都有效，除了一些小的例外，我将不得不稍后处理，有些是因为游戏还没有完全完成。

只是为了确保我能正确理解这个问题，因为我之前从未使用过较低级语言的GUI和图像。首先将图像加载到纹理中，然后将纹理添加到精灵中，然后将该精灵绘制到窗口上？

该程序完美编译，正确初始化所有内容，并且没有任何重大的无法解释的问题。除了图像没有显示。精灵在那里并以默认的单色背景颜色显示，但不显示任何图像。

我做错了什么，我该如何解决？谢谢！

// HEADERS
#include <iostream>
#include <SFML/Graphics.hpp>
#include <SFML/Graphics/Color.hpp>
#include <SFML/Graphics/Font.hpp>
#include <SFML/Graphics/Image.hpp>
#include <SFML/Graphics/Rect.hpp>
#include <SFML/Graphics/Sprite.hpp>
#include <SFML/Graphics/Texture.hpp>
#include <SFML/System/String.hpp>
#include <SFML/Window/Keyboard.hpp>

// CREATE NEW FONT
sf::Font create_font()
{
    sf::Font f;
    bool id = f.loadFromFile("/usr/share/fonts/truetype/ubuntu-font-family/Ubuntu-B.ttf");

    if (id == false)
    {
        std::cerr << "Font:\tCould not be loaded." << std::endl;
    }
    else
    {
        std::cerr << "Font:\tLoaded successfully." << std::endl;
    }

    return f;

}

// CREATE NEW SPRITE USING TEXTURE, GIVEN ARE PATH WITH COORDINATES AND DIMENSIONS
sf::Sprite load_img(std::string path, long x, long y, long w, long h)
{
    sf::Texture t;
    bool id = t.loadFromFile(path);

    if (id == false)
    {
        std::cerr << "Texture:\t" << path << "\tFailed to load." << std::endl;
    }
    else
    {
        std::cerr << "Texture:\t" << path << "\tLoaded successfully." << std::endl;
    }

    sf::Sprite s(t);
    s.setTextureRect(sf::IntRect((int)x, (int)y, (int)w, (int)h));
    s.setPosition(x, y);
    return s;
}


// MAIN FUNCTION
int main()
{
    // DECLARING/DEFINING VARIABLES
    unsigned long window_width = 512;
    unsigned long window_height = 512;
    unsigned long score = 0;
    unsigned long head_old_position_x, head_old_position_y;
    std::string title = "Snek";
    std::string wdir = "/home/kate/Documents/coding/snek/";

    // WINDOW
    sf::RenderWindow window(sf::VideoMode(window_width, window_height), title);
    window.setFramerateLimit(60);

    // SPRITES
    sf::Sprite background = load_img(wdir + "img/background.png", 0, 0, 512, 512);
    sf::Sprite head = load_img(wdir + "img/head.png", 47, 39, 8, 8);
    sf::Sprite body = load_img(wdir + "img/body.png", 39, 39, 8, 8);
    sf::Sprite poison = load_img(wdir + "img/poison.png", 119, 119, 8, 8);
    sf::Sprite trap = load_img(wdir + "img/trap.png", 159, 159, 8, 8);
    sf::Sprite candy = load_img(wdir + "img/candy.png", 199, 199, 8, 8);

    // FONT
    sf::Font font = create_font();

    // TEXT
    sf::Text score_display(title, font, 20);
    sc// HEADERS
#include <iostream>
#include <SFML/Graphics.hpp>
#include <SFML/Graphics/Color.hpp>
#include <SFML/Graphics/Font.hpp>
#include <SFML/Graphics/Image.hpp>
#include <SFML/Graphics/Rect.hpp>
#include <SFML/Graphics/Sprite.hpp>
#include <SFML/Graphics/Texture.hpp>
#include <SFML/System/String.hpp>
#include <SFML/Window/Keyboard.hpp>

// CREATE NEW FONT
sf::Font create_font()
{
    sf::Font f;
    bool id = f.loadFromFile("/usr/share/fonts/truetype/ubuntu-font-family/Ubuntu-B.ttf");

    if (id == false)
    {
        std::cerr << "Font:\tCould not be loaded." << std::endl;
    }
    else
    {
        std::cerr << "Font:\tLoaded successfully." << std::endl;
    }

    return f;

}

// CREATE NEW SPRITE USING TEXTURE, GIVEN ARE PATH WITH COORDINATES AND DIMENSIONS
sf::Sprite load_img(std::string path, long x, long y, long w, long h)
{
    sf::Texture t;
    bool id = t.loadFromFile(path);

    if (id == false)
    {
        std::cerr << "Texture:\t" << path << "\tFailed to load." << std::endl;
    }
    else
    {
        std::cerr << "Texture:\t" << path << "\tLoaded successfully." << std::endl;
    }

    sf::Sprite s(t);
    s.setTextureRect(sf::IntRect((int)x, (int)y, (int)w, (int)h));
    s.setPosition(x, y);
    return s;
}


// MAIN FUNCTION
int main()
{
    // DECLARING/DEFINING VARIABLES
    unsigned long window_width = 512;
    unsigned long window_height = 512;
    unsigned long score = 0;
    unsigned long head_old_position_x, head_old_position_y;
    std::string title = "Snek";
    std::string wdir = "/home/kate/Documents/coding/snek/";

    // WINDOW
    sf::RenderWindow window(sf::VideoMode(window_width, window_height), title);
    window.setFramerateLimit(60);

    // SPRITES
    sf::Sprite background = load_img(wdir + "/img/background.png", 0, 0, 512, 512);
    sf::Sprite head = load_img(wdir + "/img/head.png", 47, 39, 8, 8);
    sf::Sprite body = load_img(wdir + "/img/body.png", 39, 39, 8, 8);
    sf::Sprite poison = load_img(wdir + "/img/poison.png", 119, 119, 8, 8);
    sf::Sprite trap = load_img(wdir + "/img/trap.png", 159, 159, 8, 8);
    sf::Sprite candy = load_img(wdir + "/img/candy.png", 199, 199, 8, 8);

    // FONT
    sf::Font font = create_font();

    // TEXT
    sf::Text score_display(title, font, 20);
    score_display.setString(std::to_string(score));
    score_display.setPosition(5, 5);

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

            head_old_position_x = head.getPosition().x;
            head_old_position_y = head.getPosition().y;

            // MOVEMENT BASED ON KEYBOARD INPUT
            if (sf::Keyboard::isKeyPressed(sf::Keyboard::Left))
            {
                head.setPosition(head.getPosition().x - 8, head.getPosition().y);
                body.setPosition(head_old_position_x, head_old_position_y);
            }

            if (sf::Keyboard::isKeyPressed(sf::Keyboard::Up))
            {
                head.setPosition(head.getPosition().x, head.getPosition().y - 8);
                body.setPosition(head_old_position_x, head_old_position_y);
            }

            if (sf::Keyboard::isKeyPressed(sf::Keyboard::Right))
            {
                head.setPosition(head.getPosition().x + 8, head.getPosition().y);
                body.setPosition(head_old_position_x, head_old_position_y);
            }

            if (sf::Keyboard::isKeyPressed(sf::Keyboard::Down))
            {
                head.setPosition(head.getPosition().x, head.getPosition().y + 8);
                body.setPosition(head_old_position_x, head_old_position_y);
            }


            if (body.getPosition().x == candy.getPosition().x && body.getPosition().y == candy.getPosition().y)
            {
                score ++;
                score_display.setString(std::to_string(score));
            }


            // REFRESH WINDOW
            window.clear();
            window.draw(background);
            window.draw(head);
            window.draw(body);
            window.draw(poison);
            window.draw(trap);
            window.draw(candy);
            window.draw(score_display);
            window.display();
        }
    }

    return 0;
}
ore_display.setString(std::to_string(score));
    score_display.setPosition(5, 5);

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

            head_old_position_x = head.getPosition().x;
            head_old_position_y = head.getPosition().y;

            // MOVEMENT BASED ON KEYBOARD INPUT
            if (sf::Keyboard::isKeyPressed(sf::Keyboard::Left))
            {
                head.setPosition(head.getPosition().x - 8, head.getPosition().y);
                body.setPosition(head_old_position_x, head_old_position_y);
            }

            if (sf::Keyboard::isKeyPressed(sf::Keyboard::Up))
            {
                head.setPosition(head.getPosition().x, head.getPosition().y - 8);
                body.setPosition(head_old_position_x, head_old_position_y);
            }

            if (sf::Keyboard::isKeyPressed(sf::Keyboard::Right))
            {
                head.setPosition(head.getPosition().x + 8, head.getPosition().y);
                body.setPosition(head_old_position_x, head_old_position_y);
            }

            if (sf::Keyboard::isKeyPressed(sf::Keyboard::Down))
            {
                head.setPosition(head.getPosition().x, head.getPosition().y + 8);
                body.setPosition(head_old_position_x, head_old_position_y);
            }


            if (body.getPosition().x == candy.getPosition().x && body.getPosition().y == candy.getPosition().y)
            {
                score ++;
                score_display.setString(std::to_string(score));
            }


            // REFRESH WINDOW
            window.clear();
            window.draw(background);
            window.draw(head);
            window.draw(body);
            window.draw(poison);
            window.draw(trap);
            window.draw(candy);
            window.draw(score_display);
            window.display();
        }
    }

    return 0;
}

Answer 1

纹理超出范围，有关详细信息，请参阅When is an object "out of scope"?。你在load_img函数中声明了纹理，但在退出load_img并返回精灵后删除了sf::Texture t;。

所以这是一个更新的函数，在其中将纹理存储在load_img函数之外并通过引用传递它。仅显示相关部件。首先将纹理传递给load_img函数。删除sf::Texture t;。

sf::Sprite load_img(std::string path, long x, long y, long w, long h, sf::Texture& t)
{
    bool id = t.loadFromFile(path);
    [...]
}

声明一个纹理并将其传递给load_img函数。

sf::Texture headtexture;
sf::Sprite head = load_img(wdir + "img/head.png", 47, 39, 8, 8, headtexture);

如果你为所有精灵执行此操作，它会正常工作并正确显示图像/精灵。

修改 2017年9月25日

根据评论，这里是一个没有函数的最小工作示例：

// HEADERS
#include <iostream>
#include <SFML/Graphics.hpp>
#include <SFML/Graphics/Color.hpp>
#include <SFML/Graphics/Font.hpp>
#include <SFML/Graphics/Image.hpp>
#include <SFML/Graphics/Rect.hpp>
#include <SFML/Graphics/Sprite.hpp>
#include <SFML/Graphics/Texture.hpp>
#include <SFML/System/String.hpp>
#include <SFML/Window/Keyboard.hpp>

// MAIN FUNCTION
int main()
{
    // DECLARING/DEFINING VARIABLES
    unsigned long window_width = 512;
    unsigned long window_height = 512;
    std::string title = "Snek";
    std::string wdir = "/home/kate/Documents/coding/snek/";

    // WINDOW
    sf::RenderWindow window(sf::VideoMode(window_width, window_height), title);
    window.setFramerateLimit(60);

    // SPRITES
    sf::Texture headtexture;
    sf::Sprite head;

    headtexture.loadFromFile(wdir + "img/head.png");
    head.setTexture(headtexture);
    head.setTextureRect(sf::IntRect(47, 39, 8, 8));
    head.setPosition(30, 30);

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

            // REFRESH WINDOW
            window.clear();
            window.draw(head);
            window.display();
        }
    }

    return 0;
}

Answer 2

您遗失了对纹理的引用。在您的情况下，纹理是load_img()函数中的局部变量。

当任何精灵使用它时，你应该保持你的纹理加载和可用。

我建议您阅读解释此问题的SFML教程的this部分。

Answer 3

好的，我想我已经得到了它。

可能没有显示任何内容，因为您在事件循环中拥有所有绘图内容

尝试将这些内容放在while(window.isOpen())循环范围内。