c++ - 为什么我的自定义图形项在基于 Qt 的 C++ GUI 应用程序中不断重新绘制？

Question

我的应用程序有一个 QMdiArea，在其中显示子窗口，其中包含 QGraphicsView 派生 View (GfxInteractiveView) 的实例，这反过来可视化包含自定义 QGraphicsItem 派生项目的场景。

/// An image item which is displayed as the background of a scene.
class GfxImageItem : public QObject, public QGraphicsPixmapItem
{
    Q_OBJECT

protected:
    GfxInteractiveImgView *view_;
    QPixmap pixmap_;

    QList<GfxPointItem *> pointItems_;

public:
    GfxImageItem(GfxInteractiveImgView *view);

    // set the pixmap to the image loaded from this path
    bool load(const QString &path);

    // normally not overriden, here just for tracing 
    virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
    {
        QLOG("Painting image"); // homebrew macro for tracing
        QGraphicsPixmapItem::paint(painter, option, widget);
    }
};

/// A generated image drawn at the foreground of a scene. 
class GfxMapItem : public QGraphicsPixmapItem
{

public:
    GfxMapItem(QGraphicsItem *item);

    void regenerateMap();

    // same as GfxMapItem, here just for tracing
    virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
};

到目前为止一切顺利，但我还有另一个项目 GfxPointItem，它是完全自定义的，具有实际执行某些操作的 paint()，当我将其添加到场景中时，其中一个内核的 CPU 使用率跳升至满所有层次结构中的项目进入重绘循环，只要窗口可见或场景中存在自定义项目，该循环就会继续。发生这种情况时看一下堆栈表明我的函数都不负责调用 paint()，事件是在事件循环中生成的。这是 GfxPointItem 的代码:

/// A draggable item representing an analysis point on the map, drawn on top of the map.
class GfxPointItem : public QGraphicsObject
{
    Q_OBJECT

protected:
    GfxImageItem *imgParent_;
    GfxInteractiveImgView *view_;
    int size_, fontSize_;
    QColor color_, oldColor_;
    qreal paintScale_;
    QRectF boundingRect_;
    bool active_, static_;
    QStaticText pointText_, valueText_;

public:
    GfxPointItem(GfxImageItem *parent, GfxInteractiveImgView *view, const QPointF &pos);

    void setActive(bool arg);
    void setStatic(bool arg);
    void setColor(const QColor &color) { color_ = color; update(); }

    virtual QRectF boundingRect() const { return boundingRect_; }
    virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);

signals:
    void changedPos(int index, QPointF newpos);

public slots:
    void setPaintScale(qreal value);
    void setPointText(const QString &text);
    void setValueText(const QString &text);

protected:
    void updateBoundRect();
    void updatePointText();
    QPoint valueTextPos() const;
    QPoint pointTextPos() const;
};


GfxPointItem::GfxPointItem(GfxImageItem *parent, GfxInteractiveImgView *view, const QPointF &pos, int index) : QGraphicsObject(parent),
    imgParent_(parent),
    view_(view),
    index_(index), size_(8), fontSize_(8), 
    color_(Qt::black),
    paintScale_(view->invscale()),
    drawLabel_(true), active_(false), static_(false), floatPrec_(false)
{
    QLOGX("Creating new at " << pos.x() << "," << pos.y() << ", index: " << index);
    setPos(pos);
    updatePointText();
    connect(view, SIGNAL(scaleChanged(qreal)), this, SLOT(setPaintScale(qreal)));
}

/// An inactive point wil not respond to hover events and will not be movable.
void GfxPointItem::setActive(bool arg)
{
    QLOGX("Setting active state: " << arg);
    active_ = arg;
    setAcceptHoverEvents(arg);
    setFlag(QGraphicsItem::ItemIsMovable, arg);
}

/// Set or disable static mode on point. In static mode, the point text is not updated when changing position, so it can retain a constant label.
void GfxPointItem::setStatic(bool arg)
{
    QLOGX("Setting static mode: " << arg);
    static_ = arg;
}

void GfxPointItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    QLOGX("Painting point");
    static const int margin = 2;
    setScale(paintScale_);
    QPen pen;
    pen.setWidth(1);
    pen.setColor(color_);
    painter->setPen(pen);

    // paint the centerpoint marker (two crossed lines)
    painter->drawLine(QPointF(-size_, 0), QPointF( size_, 0));
    painter->drawLine(QPointF(0, -size_), QPointF(0,  size_));

    // the label box and the two static text lines inside
    pen.setWidth(0);
    painter->setPen(pen);

    QFont font;
    font.setPointSize(fontSize_);
    painter->setFont(font);

    QBrush brush(Qt::SolidPattern);
    brush.setColor(QColor(255, 255, 127)); // sand yellow
    painter->setBrush(brush);

    // point text size, value text size
    QSizeF pts = pointText_.size(), 
           vts = valueText_.size();

    // point text position, value text position
    QPoint vtp = valueTextPos(),
           ptp = pointTextPos();

    // point id and position label and value indicator label in a rectangular box
    int shift = (valueText_.text().isEmpty()) ? 0 : vts.height();
    QRectF rect(ptp.x()-margin, ptp.y(), std::max(pts.width(), vts.width())+margin, pts.height() + shift);
    painter->drawRect(rect);
    painter->drawStaticText(ptp, pointText_);
    painter->drawStaticText(vtp, valueText_);
}

void GfxPointItem::setPaintScale(qreal value) 
{ 
    QLOGX("Updating scale: " << value);
    paintScale_ = value; 
    update(); 
}

void GfxPointItem::setPointText(const QString &text)
{
    QLOGX("Setting text: " << text);
    pointText_.setText(text);
    updateBoundRect(); 
    update();
}

void GfxPointItem::setValueText(const QString &text) 
{ 
    QLOGX("Setting value text: " << text);
    valueText_.setText(text); 
    updateBoundRect(); 
    update();
}

void GfxPointItem::updateBoundRect()
{
    QLOGX("Updating bounding rect");
    boundingRect_.setRect(- size_, pointTextPos().y(), 
        (2 * size_) + std::max(pointText_.size().width(), valueText_.size().width()), 
        (2 * size_) + pointText_.size().height() + valueText_.size().height());
}

void GfxPointItem::updatePointText()
{
    QLOGX("Updating point text");
    pointText_.setText("P" + QString::number(index_ + 1) + " (" 
        + (floatPrec_ ? QString::number(pos().x()) : QString::number(std::floor(pos().x()))) + "," 
        + (floatPrec_ ? QString::number(pos().y()) : QString::number(std::floor(pos().y()))) + ")");

    updateBoundRect();
    update();
}

void GfxPointItem::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
{
    QLOGX("Mouse move");
    QPointF p = pos();
    QPointF ep = event->pos();

    QGraphicsItem::mouseMoveEvent(event);

    if (!static_) updatePointText();
    emit changedPos(index_, pos());
}

我不知道为什么事件循环不断地重新绘制项目。我什至没有注意到这一点，但我在显示标准 QFileDialog::getExistingDirectory() 时遇到了问题，当带有图形项目的窗口可见时，它甚至无法绘制，因为重新绘制偷走了所有执行时间主线程远离它，导致卡住。之后，我向绘制函数添加了跟踪语句，并在几秒钟后在日志文件中发现了数万个条目，而应用程序似乎什么也没做。在任务管理器中，当窗口可见时(在 4 核处理器上)CPU 使用率约为 25%，当我关闭它时它下降到 0。

我的代码都没有强制这些重绘，那是什么？我如何调试事件循环以找到此行为的根源，这会减慢我的应用程序并导致卡住？

谢谢!

Qt 版本是最新的 5.0.2 二进制包，应用程序是使用 Visual C++ 2012 for x64 编译的。

Answer 1

在我看来，当在 paint 中调用 setScale 时，它连接到 setPaintScale，然后调用 QWidget 的 update 函数，然后使该区域无效，当它返回到主事件循环时会导致 repaint .

因此，每次调用 paint 方法时，您最终都会获得 1 个 paint required 事件。