QtCharts图形移动和缩放

功能

实现QtCharts曲线图移动和缩放：

1. 按住鼠标左键拖动曲线可移动曲线；
2. 滚动鼠标滚轮实现图形X轴方向的缩放；
3. 安装Ctrl，滚动鼠标滚轮实现图形Y轴方向的缩放；
4. 按鼠标右键恢复图形初始状态;
5. 缩放过程以鼠标当前位置为缩放中心；
6. 鼠标移动过程中会在左上角显示当前坐标。

实现

继承QChartView，主要重新实现鼠标事件和键盘事件。

1. 移动图形利用QChart的scroll函数；
   void scroll(qreal dx, qreal dy, const QRectF &rect = QRectF());
   鼠标按下时，记录按下状态，并记录当前坐标位置，在移动事件内计算鼠标移动的距离，以此设置图形滚动的距离，即可实现移动
2. 缩放则设置当前坐标轴的显示范围；
   void setRange(const QVariant &min, const QVariant &max);

代码

1. 实现移动

void ChartView::mousePressEvent(QMouseEvent *event)
{
    
    
	if (event->button() == Qt::LeftButton)
	{
    
    
        m_lastPoint = event->pos();
        m_isPress = true;
	}
}

void ChartView::mouseMoveEvent(QMouseEvent *event)
{
    
    
	if (!m_coordItem)
	{
    
    
		m_coordItem = new QGraphicsSimpleTextItem(this->chart());
		m_coordItem->setZValue(5);
		m_coordItem->setPos(100, 60);
		m_coordItem->show();
	}
	const QPoint curPos = event->pos();
	QPointF curVal = this->chart()->mapToValue(QPointF(curPos));
	QString coordStr = QString("X = %1, Y = %2").arg(curVal.x()).arg(curVal.y());
	m_coordItem->setText(coordStr);

	if (m_isPress)
	{
    
    
		QPoint offset = curPos - m_lastPoint;
		m_lastPoint = curPos;
		if (!m_alreadySaveRange)
		{
    
    
			this->saveAxisRange();
			m_alreadySaveRange = true;
		}
		this->chart()->scroll(-offset.x(), offset.y());
	}
}

void ChartView::mouseReleaseEvent(QMouseEvent *event)
{
    
    
	m_isPress = false;
	if (event->button() == Qt::RightButton)
	{
    
    
		if (m_alreadySaveRange)
		{
    
    
			this->chart()->axisX()->setRange(m_xMin, m_xMax);
			this->chart()->axisY()->setRange(m_yMin, m_yMax);
		}
	}
}

2. 实现缩放

void ChartView::wheelEvent(QWheelEvent *event)
{
    
    
   const QPoint curPos = event->pos();
   QPointF curVal = this->chart()->mapToValue(QPointF(curPos));

   if (!m_alreadySaveRange)
   {
    
    
   	this->saveAxisRange();
   	m_alreadySaveRange = true;
   }

   const double factor = 1.5;//缩放比例
   if (m_ctrlPress)
   {
    
    //Y轴
   	QValueAxis *axisY = dynamic_cast<QValueAxis*>(this->chart()->axisY());
   	const double yMin = axisY->min();
   	const double yMax = axisY->max();
   	const double yCentral = curVal.y();

   	double bottomOffset;
   	double topOffset;
   	if (event->delta() > 0)
   	{
    
    //放大
   		bottomOffset = 1.0 / factor * (yCentral - yMin);
   		topOffset = 1.0 / factor * (yMax - yCentral);
   	}
   	else
   	{
    
    //缩小
   		bottomOffset = 1.0 * factor * (yCentral - yMin);
   		topOffset = 1.0 * factor * (yMax - yCentral);
   	}

   	this->chart()->axisY()->setRange(yCentral - bottomOffset, yCentral + topOffset);
   }
   else
   {
    
    //X轴
   	QValueAxis *axisX = dynamic_cast<QValueAxis*>(this->chart()->axisX());
   	const double xMin = axisX->min();
   	const double xMax = axisX->max();
   	const double xCentral = curVal.x();

   	double leftOffset;
   	double rightOffset;
   	if (event->delta() > 0)
   	{
    
    //放大
   		leftOffset = 1.0 / factor * (xCentral - xMin);
   		rightOffset = 1.0 / factor * (xMax - xCentral);
   	}
   	else
   	{
    
    //缩小
   		leftOffset = 1.0 * factor * (xCentral - xMin);
   		rightOffset = 1.0 * factor * (xMax - xCentral);
   	}

   	this->chart()->axisX()->setRange(xCentral - leftOffset, xCentral + rightOffset);
   }
}

完整代码和示例程序请在QtCharts图形移动和缩放下载。