**Course Title:** Qt 6 Application Development with C++ **Section Title:** Graphics and Animations in Qt **Topic:** Creating custom graphics items and rendering them on screen ### Overview In this topic, we'll delve into the world of custom graphics rendering in Qt 6. We'll explore how to create custom graphics items, render them on screen, and interact with them using the mouse and keyboard. By the end of this topic, you'll have a solid understanding of how to create complex, custom graphics applications using Qt 6. ### Creating Custom Graphics Items To create a custom graphics item in Qt 6, you need to subclass `QGraphicsItem` or one of its subclasses, such as `QGraphicsEllipseItem` or `QGraphicsRectItem`. Let's create a simple custom graphics item that displays a rectangle with a red border. ```cpp #include <QGraphicsItem> #include <QPainter> #include <QRectF> class CustomGraphicsItem : public QGraphicsItem { public: CustomGraphicsItem(QGraphicsItem *parent = nullptr) : QGraphicsItem(parent) { setRect(QRectF(0, 0, 100, 100)); } protected: void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget = nullptr) override { painter->setPen(Qt::red); painter->setBrush(Qt::transparent); painter->drawRect(boundingRect()); } }; ``` In this example, we create a custom graphics item called `CustomGraphicsItem` that inherits from `QGraphicsItem`. We override the `paint` function to draw a rectangle with a red border. ### Rendering Custom Graphics Items To render our custom graphics item on screen, we need to add it to a `QGraphicsScene` and display it using a `QGraphicsView`. Let's create a simple application that displays our custom graphics item. ```cpp #include <QApplication> #include <QGraphicsScene> #include <QGraphicsView> #include "customgraphicsitem.h" int main(int argc, char **argv) { QApplication app(argc, argv); QGraphicsScene scene; CustomGraphicsItem *item = new CustomGraphicsItem(); scene.addItem(item); QGraphicsView view(&scene); view.show(); return app.exec(); } ``` In this example, we create a `QApplication` and a `QGraphicsScene`. We then create an instance of our custom graphics item and add it to the scene using the `addItem` function. Finally, we create a `QGraphicsView` and display it using the `show` function. ### Interacting with Custom Graphics Items To interact with our custom graphics item using the mouse and keyboard, we need to override the `mousePressEvent` and `keyPressEvent` functions in our custom graphics item class. ```cpp void CustomGraphicsItem::mousePressEvent(QGraphicsSceneMouseEvent *event) { qDebug() << "Mouse pressed"; QGraphicsItem::mousePressEvent(event); } void CustomGraphicsItem::keyPressEvent(QKeyEvent *event) { qDebug() << "Key pressed"; QGraphicsItem::keyPressEvent(event); } ``` In this example, we override the `mousePressEvent` and `keyPressEvent` functions to print a debug message when the mouse or keyboard is pressed. ### Key Concepts * Creating custom graphics items by subclassing `QGraphicsItem` or its subclasses. * Rendering custom graphics items on screen using `QGraphicsScene` and `QGraphicsView`. * Interacting with custom graphics items using the mouse and keyboard. ### Practical Takeaways * Create custom graphics items by subclassing `QGraphicsItem` and overriding the `paint` function. * Add custom graphics items to a `QGraphicsScene` and display them using a `QGraphicsView`. * Interact with custom graphics items by overriding the `mousePressEvent` and `keyPressEvent` functions. ### Conclusion In this topic, we explored how to create custom graphics items and render them on screen using Qt 6. We also interacted with our custom graphics item using the mouse and keyboard. By following these steps, you can create complex, custom graphics applications using Qt 6. For more information on custom graphics items in Qt 6, you can refer to the following resources: * [Qt 6 Graphics View Framework Documentation](https://doc.qt.io/qt-6/graphicsview.html) * [Qt 6 Graphics Item Documentation](https://doc.qt.io/qt-6/qgraphicsitem.html) Leave a comment below if you have any questions or need further clarification on any of the concepts covered in this topic. We'll be covering animations in the next topic, 'Using QPropertyAnimation and QSequentialAnimationGroup for animations.'