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我的应用程序有一个 QMdiArea，其中显示了包含 QGraphicsView 派生视图 (GfxInteractiveView) 实例的子窗口，这些视图反过来可视化包含自定义 QGraphicsItem 派生项的场景。

/// 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);
};

到目前为止一切都很好，但我还有另一个项目 GfxPointItem，它是完全自定义的，它具有实际执行某些操作的 paint()，当我将它添加到场景中时，CPU 使用率在其中一个核心上像所有项目一样跳到满在层次结构中输入一个重绘循环，只要窗口可见或场景中存在自定义项，该循环就会持续。发生这种情况时查看堆栈表明我的函数都不负责调用paint()，事件是在事件循环上生成的。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重新绘制项目。我什至不会注意到这一点，但是我在显示标准 QFileDialog::getExistingDirectory() 时遇到了问题，当带有图形项的窗口可见时，它甚至无法绘制，因为重绘偷走了所有执行时间主线程远离它，导致冻结。之后，我在绘制函数中添加了跟踪语句，并在几秒钟后在日志文件中找到了数万条条目，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%，当我关闭它时它降至 0。

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

谢谢！

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

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1 回答 1

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在我看来，当调用它时setScale，paint它连接到setPaintScale，然后调用 QWidget 的update函数，然后使该区域无效，并且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。

于 2013-06-27T09:01:17.023 回答