SFML中叠加透明视图无法绘制问题求助

Hey there, let's dig into why your overlay view isn't showing up and get it working properly! I've gone through your code and spotted a few key mistakes that are causing the problem.

Key Issues in Your Original Code #

• Incorrect Viewport Setup: sf::View::setViewport() expects normalized coordinates (values between 0 and 1) that represent a fraction of the window's size/position. You passed in projectsBox.getGlobalBounds() which uses pixel coordinates—this pushes your viewport completely outside the window, so nothing drawn to it ever appears.
• Misconfigured Origin: Using negative values for setOrigin() was shoving your randomBox outside the viewable area of your overlay view.
• Missing Event Handling: You didn't include an event loop to handle window closure (small but important for usability!).

Fixed Code with Explanations #

Here's the corrected version of your code, with comments breaking down each change:

#include <SFML/Graphics.hpp>

int main() {
    sf::RenderWindow mainWindow;
    // Removed the invalid 300 parameter in VideoMode (it's bits per pixel, optional and usually 32)
    mainWindow.create(sf::VideoMode(800, 900), "SFML Works", sf::Style::Close);

    // Visual border for our overlay area (only for reference)
    sf::RectangleShape projectsBox(sf::Vector2f(400, 225));
    // Use setPosition() instead of negative setOrigin() to place the box
    projectsBox.setPosition(10, 130);
    projectsBox.setOutlineColor(sf::Color::Black);
    projectsBox.setOutlineThickness(10);
    projectsBox.setFillColor(sf::Color::Transparent);

    // Create our overlay view
    sf::View projectsView;
    // Convert pixel coordinates to normalized viewport values
    float winWidth = mainWindow.getSize().x;
    float winHeight = mainWindow.getSize().y;
    sf::FloatRect viewport(
        projectsBox.getPosition().x / winWidth,
        projectsBox.getPosition().y / winHeight,
        projectsBox.getSize().x / winWidth,
        projectsBox.getSize().y / winHeight
    );
    projectsView.setViewport(viewport);
    // Set the view's visible area to match our projectsBox size/position
    projectsView.setSize(projectsBox.getSize());
    projectsView.setCenter(projectsBox.getPosition() + projectsBox.getSize() / 2.f);

    // Box to draw inside the overlay view
    sf::RectangleShape randomBox(sf::Vector2f(100, 100));
    // Set origin to the center so positioning is intuitive
    randomBox.setOrigin(randomBox.getSize() / 2.f);
    // Place it at the center of our overlay view
    randomBox.setPosition(projectsView.getCenter());
    randomBox.setOutlineColor(sf::Color::Black);
    randomBox.setOutlineThickness(10);
    randomBox.setFillColor(sf::Color::Yellow);

    while (mainWindow.isOpen()) {
        sf::Event event;
        // Handle window events (like closing the window)
        while (mainWindow.pollEvent(event)) {
            if (event.type == sf::Event::Closed)
                mainWindow.close();
        }

        mainWindow.clear(sf::Color::White);

        // First draw default view content (our border box)
        mainWindow.setView(mainWindow.getDefaultView());
        mainWindow.draw(projectsBox);

        // Switch to overlay view and draw its content
        mainWindow.setView(projectsView);
        mainWindow.draw(randomBox);

        mainWindow.display();
    }

    return 0;
}

Why This Works #

• Normalized Viewport: By dividing the box's pixel position/size by the window's dimensions, we tell SFML exactly where on the window the overlay view should appear.
• Proper View Configuration: setSize() and setCenter() ensure the view's coordinate space matches our overlay area, so content drawn to it aligns correctly with the border box.
• Intuitive Positioning: Setting randomBox's origin to its center makes it easy to place the box exactly where we want it in the overlay.
• Transparent Empty Areas: Since we only draw content within the overlay view's viewport, any empty space in the view stays transparent (showing the default view's content behind it).

内容的提问来源于stack exchange，提问作者Jacob