Making a Qt Widget Fullscreen: Code Examples

Making a Widget Fullscreen

In Qt, the QWidget::showFullScreen() member function is the primary way to enter fullscreen mode for a widget. It expands the widget to fill the entire screen, excluding the system taskbar or menu bar (depending on the platform).

#include <QApplication>
#include <QWidget>

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

  QWidget myWidget;
  myWidget.showFullScreen(); // Make the widget fullscreen

  return app.exec();
}

Key Points

• Platform Considerations
  While showFullScreen() generally removes window decorations (title bar, borders), the exact behavior might vary slightly across platforms due to differences in window management.
• Applies to Top-Level Widgets
  showFullScreen() is typically used with top-level widgets like QMainWindow or custom widget classes that inherit from QWidget and set the Qt::WA_ לנווט בכל החלונות (Window) flag. This flag tells Qt to treat the widget as a separate window, enabling fullscreen behavior.

Alternative Approach (Less Common)

In some rare cases, you might want to achieve a fullscreen effect for a child widget within a top-level window. While not directly supported by QWidget, you can combine techniques like setting Qt::WindowStaysOnTopHint and Qt::FramelessWindowHint flags along with manual positioning and sizing to create a visually similar effect. However, this approach can be less reliable and have compatibility issues across platforms.

• For more complex fullscreen behavior, explore platform-specific APIs or third-party libraries.
• Fullscreen mode might interact with system events like task switching or notifications. Consider handling these events appropriately in your application logic.

---

Simple Fullscreen Toggle (Top-Level Widget)

#include <QApplication>
#include <QPushButton>
#include <QWidget>

class FullscreenWidget : public QWidget {
  Q_OBJECT

public:
  FullscreenWidget(QWidget *parent = nullptr) : QWidget(parent) {
    QPushButton* fullscreenButton = new QPushButton("Toggle Fullscreen", this);
    connect(fullscreenButton, &QPushButton::clicked, this, &FullscreenWidget::toggleFullscreen);
  }

private slots:
  void toggleFullscreen() {
    if (isFullScreen()) {
      // Exit fullscreen
      showNormal();
    } else {
      // Enter fullscreen
      showFullScreen();
    }
  }
};

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

  FullscreenWidget fullscreenWidget;
  fullscreenWidget.show();

  return app.exec();
}

This example creates a custom FullscreenWidget class that inherits from QWidget. It has a button labeled "Toggle Fullscreen" that emits a signal when clicked. The toggleFullscreen slot checks if the widget is currently fullscreen and resizes it accordingly.

Fullscreen with Exit on Escape (Child Widget)

#include <QApplication>
#include <QKeyEvent>
#include <QLabel>
#include <QWidget>

class MyWindow : public QWidget {
  Q_OBJECT

public:
  MyWindow(QWidget *parent = nullptr) : QWidget(parent) {
    fullscreenLabel = new QLabel("Press Esc to Exit Fullscreen", this);
    fullscreenLabel->setAlignment(Qt::AlignCenter);
  }

protected:
  void keyPressEvent(QKeyEvent *event) override {
    if (event->key() == Qt::Key_Escape) {
      // Exit fullscreen when Esc is pressed
      showNormal();
    }
  }

private:
  QLabel* fullscreenLabel;
};

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

  MyWindow window;
  // Assuming window is a top-level widget
  window.showFullScreen();

  return app.exec();
}

This example demonstrates a child widget (MyWindow) with a label displayed in fullscreen mode. It overrides the keyPressEvent to listen for the Esc key and exits fullscreen when pressed.

---

QWidget::showMaximized()

• Usage:
• May be a good choice if you still want users to interact with the system tray or other elements outside your application.
• Fills the entire screen area excluding the taskbar or menu bar (similar to showFullScreen()).

myWidget.showMaximized();

Manual Sizing and Positioning

• This approach offers more granular control but requires handling window decorations (title bar, borders) manually.
• Set the widget's size and position to cover the entire screen area you desire.
• Get the screen dimensions using QApplication::desktop()->screenGeometry().

Platform-Specific APIs

• Be aware of potential compatibility issues.
• Qt doesn't offer a unified interface for this, so research is needed for each platform (Windows, macOS, Linux).
• Explore APIs provided by the underlying operating system for more fine-grained fullscreen control.

Third-Party Libraries

• Evaluate their benefits and potential dependencies before integrating them.

Choosing the Right Alternative

The best alternative depends on your specific requirements:

• Third-party libraries can offer additional functionality but might introduce complexity.
• For more control over window decorations or fullscreen behavior, consider manual sizing or platform-specific APIs.
• If you just need the widget to fill the available screen space, showFullScreen() or showMaximized() might suffice.

• Fullscreen mode can interact with system events like task switching or notifications. Manage these events in your application logic.
• Remember to handle exiting fullscreen appropriately (e.g., toggle button, Esc key handling).