qt中使用鼠标绘制直线图元的例子

以下是一个简单的示例，演示如何在Qt中使用鼠标绘制直线图：

#include <QtGui>
#include <Widgets>

class Line : public QGraphicsLineItem
{
public:
    Line(const QLineF& line) : QGraphicsLineItem(line) {}
    QRectF boundingRect() const override { return pen().widthF() + 20.0 + QGraphicsLineItem::boundingRect(); }
    QPainterPath shape() const override
    {
        QPainterPath path = QGraphicsLineItem::shape();
        path.addRect(boundingRect());
        return path;
    }
    void paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget) override
    {
        if (option->state & QStyle::State_Selected)
        {
            painter->setPen(QPen(option->palette.windowText(), 0, Qt::DotLine));
            painter->drawRect(boundingRect());
        }
        QGraphicsLineItem::paint(painter, option, widget);
    }
};

class GraphicsView : public QGraphicsView
{
public:
    GraphicsView(QWidget* parent = nullptr) : QGraphicsView(parent), m_isDrawing(false), m_line(nullptr)
    {
        setRenderHint(QPainter::Antialiasing);
        setDragMode(QGraphicsView::RubberBandDrag);
        setOptimizationFlag(QGraphicsView::DontAdjustForAntialiasing);
        setViewportUpdateMode(QGraphicsView::SmartViewportUpdate);
        setSelectionMode(QGraphicsView::SingleSelection);
    }

protected:
    void mousePressEvent(QMouseEvent* event) override
    {
        if (event->button() == Qt::LeftButton)
        {
            m_startPos = mapToScene(event->pos());
            m_isDrawing = true;
        }
        QGraphicsView::mousePressEvent(event);
    }

    void mouseMoveEvent(QMouseEvent* event) override
    {
        if (m_isDrawing)
        {
            if (!m_line)
            {
                m_line = new Line(QLineF(m_startPos, mapToScene(event->pos())));
                scene()->addItem(m_line);
            }
            else
            {
                m_line->setLine(QLineF(m_startPos, mapToScene(event->pos())));
            }
        }
        QGraphicsView::mouseMoveEvent(event);
    }

    void mouseReleaseEvent(QMouseEvent* event) override
    {
        if (event->button() == Qt::LeftButton && m_isDrawing)
        {
            m_isDrawing = false;
            m_line = nullptr;
        }
        QGraphicsView::mouseReleaseEvent(event);
    }

private:
    bool m_isDrawing;
    QPointF m_startPos;
    Line* m_line;
};

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

    QGraphicsScene scene;
    GraphicsView view(&scene);
    view.setRenderHint(QPainter::Antialiasing);
    view.setScene(&scene);
    view.setDragMode(QGraphicsView::RubberBandDrag);

    QGraphicsLineItem* line = new QGraphicsLineItem(QLineF(0.0, 0.0, 100.0, 100.0));
    line->setPen(QPen(Qt::red, 2));
    scene.addItem(line);

    QGraphicsEllipseItem* ellipse = new QGraphicsEllipseItem(QRectF(0.0, 0.0, 100.0, 100.0));
    ellipse->setPen(QPen(Qt::blue, 2));
    ellipse->setBrush(QBrush(Qt::green));
    scene.addItem(ellipse);

    view.setSceneRect(-150, -150, 300, 300);
    view.setFixedSize(300, 300);
    view.show();

    return app.exec();
}

该示例演示了如何使用QGraphicsView和QGraphicsScene来绘制直线。在鼠标按下时，记录起始位置，并在鼠标移动时绘制直线。在鼠标释放时，停止绘制。该示例还演示了如何添加其他类型的图元，如椭圆和直线。