沿QPainterPath设置椭圆动画

Question

我有一堆椭圆，它们最初排在路径的顶部，应该沿着QPainterPath移动。我让它在第一个椭圆上工作，但我不知道如何得到其他椭圆的正确位置。

有没有一种方法可以检查它是否通过了路径的末端并将其移回起点？

class Animation : public QAbstractAnimation
{
  public:
    Animation(const QPainterPath& path, QObject *parent = Q_NULLPTR);
    virtual void updateCurrentTime(int ms) override;
    virtual int duration() const override;
    QPainterPath mPath;
    QVector<EllipseGraphicsItem*> mAnimationElements;
};


Animation::Animation (const QPainterPath& path, QObject *parent) : QAbstractAnimation(parent)
, mPath(path)
{
    qreal pos = 0;
    qreal length = mPath.length();
    while (pos < length)
    {
        qreal percent = path.percentAtLength(pos);
        QPointF pointAtPercent = path.pointAtPercent(percent);
        pos += 40;
        EllipseGraphicsItem * item = new EllipseGraphicsItem(parentItem());
        mAnimationElements.append(item);
        item->setPos(pointAtPercent);
    }
}

void Animation::updateCurrentTime(int ms)
{
     QPointF point = mPath.pointAtPercent(qreal(ms) / 6000);

     if (mAnimationElements.size() > 0)
          mAnimationElements[0]->setPos(point);

     for (int i = 0; i < mAnimationElements.size(); i++) {
         // how to update each circle's position?
     }
}

开始动画：

QPainterPath path;
path.moveTo(10, 10);
path.lineTo(QPointF(500, 10));
path.lineTo(QPointF(500, 700));
path.lineTo(QPointF(10, 700));
Animation *animation = new Animation(path, this);
animation->setLoopCount(-1);
animation->start();

Answer 1

Imho，使用带有QPropertyAnimation的QGraphicsObject会更容易

使用在0和路径长度之间变化的属性，并通过根据元素的值及其在列表中的位置来计算元素的位置来放置元素。

一个简单的例子：

class AnimatedEllipses: public QGraphicsObject
{
    Q_OBJECT
    Q_PROPERTY(int progress READ progress WRITE setProgress)
private:
    QGraphicsPathItem path;
    QList<QGraphicsEllipseItem*> ellipses;
    int propProgress;
public:
    int progress() const { return propProgress;}
    void setProgress(int value)
    {
        propProgress = value;
        int index = 0;
        for (QGraphicsEllipseItem* ellipse: ellipses)
        {
            // Keep value between 0 and length.
            int lgt = (propProgress + index * 40) % int(path.path().length());
            qreal percent = path.path().percentAtLength(lgt);
            ++index;
            ellipse->setPos(path.path().pointAtPercent(percent));
        }
    }
    AnimatedEllipses(QPainterPath const& path): QGraphicsObject(), path(path), propProgress(0)
    {
        qreal pos = 0;
        qreal length = path.length();
        while (pos < length)
        {
            qreal percent = path.percentAtLength(pos);
            QPointF pointAtPercent = path.pointAtPercent(percent);
            pos += 40;
            QGraphicsEllipseItem * item = new QGraphicsEllipseItem(-10, -10, 20, 20, this);
            item->setPos(pointAtPercent);
            ellipses << item;
        }

        QPropertyAnimation* animation = new QPropertyAnimation(this, "progress");
        animation->setStartValue(0);
        animation->setEndValue(length);
        animation->setDuration(10000);
        animation->setLoopCount(-1);
        animation->start();
    }



    // QGraphicsItem interface
public:
    QRectF boundingRect() const { return path.boundingRect();}
    void paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget){}
};

模使您可以为每个椭圆创建一个无限循环。