Question

我正在试图弄清楚如何使用QCPLayer仅重新绘制图中的某些项目。

qcustomplot documentation声明：

如果您经常需要调用完整的QCustomPlot :: replot，因为非复杂对象（例如项目）在图中具有相对静态但复杂的图形时已更改，请考虑将定期更改的对象放置在自己的图层上并将其模式（QCPLayer :: setMode）设置为QCPLayer :: lmBuffered。这使得QCustomPlot为该层分配一个专用的绘制缓冲区，并允许使用QCPLayer :: replot单独重新绘制它，独立于包含可能复杂和慢速图形的其他层。有关详细信息，请参阅相应方法的文档。

我正在尝试在下面的示例中执行此操作：

我通过继承QCustomPlot来创建自定义 qcustomplot：

QCustomPlot_custom.h

#pragma once
#include "qcustomplot.h"    
#define USING_LAYER false

struct QCPCursor{
   QCPItemLine *hLine;
   QCPItemLine *vLine;
   QCPItemText* cursorText;
};

class QCustomPlot_custom :
   public QCustomPlot
{
   Q_OBJECT    
private slots:
   void mouseMove(QMouseEvent*);

public:
   QCustomPlot_custom(QWidget* parent = NULL);
   ~QCustomPlot_custom(){}
private:
   QCPLayer* cursorLayer;
   QCPCursor cursor;   
   void manageCursor(double x, double y, QPen pen);
public:
   void init(QVector<double> xdata, QVector<double> ydata);
};

此类初始化一些数据以进行绘图。它还会重载mouseMove事件以控制自定义光标。 USING_LAYER设置为true表示自定义光标已添加到其自己的图层（cursorLayer）。

通过将USING_LAYER设置为false，我得到了所需的效果，如下所示：

光标由水平和垂直线以及坐标显示。

如果我在图中有很多图形和/或每个图形中有很多点，我会在移动光标时看到延迟。（这就是我希望能够通过在图层中设置光标来重新绘制光标的原因。）

QCustomPlot_custom.cpp

QCustomPlot_custom::QCustomPlot_custom(QWidget* parent)
{
   connect(this, SIGNAL(mouseMove(QMouseEvent*)), this, SLOT(mouseMove(QMouseEvent*)));   
   QCustomPlot::setInteraction(QCP::iRangeDrag, true);
   QCustomPlot::setInteraction(QCP::iRangeZoom, true);
   if (USING_LAYER){
      this->addLayer("cursorLayer", 0, QCustomPlot::limAbove);
      cursorLayer = new QCPLayer(this, "cursorLayer");
      cursorLayer->setMode(QCPLayer::lmBuffered);
   }
}

void QCustomPlot_custom::init(QVector<double> xdata, QVector<double> ydata)
{   
   this->addGraph();
   this->graph(0)->setData(xdata, ydata);

   QColor colorPen(10, 25, 180, 255);
   QPen pen;
   pen.setWidth(50);
   pen.setColor(colorPen);
   this->graph()->setLineStyle(QCPGraph::lsLine);
   this->graph()->setPen(QPen(colorPen));
   this->xAxis->setLabel("X-axis");
   this->yAxis->setLabel("Y-axis");      
   this->rescaleAxes();
   this->replot();
}

void QCustomPlot_custom::mouseMove(QMouseEvent* event)
{
   //Cursor coordinates:
   double x = this->xAxis->pixelToCoord(event->pos().x());
   double y = this->yAxis->pixelToCoord(event->pos().y());
   manageCursor(x, y, QPen(Qt::DashDotLine));            
   if (USING_LAYER)
      cursorLayer->replot(); 
   else
      this->replot();
}

void QCustomPlot_custom::manageCursor(double x, double y, QPen pen)
{
   if (cursor.hLine)
      this->removeItem(cursor.hLine);
   cursor.hLine = new QCPItemLine(this);   
   cursor.hLine->setPen(pen);
   cursor.hLine->start->setCoords(-QCPRange::maxRange, y);
   cursor.hLine->end->setCoords(QCPRange::maxRange, y);

   if (cursor.vLine)
      this->removeItem(cursor.vLine);
   cursor.vLine = new QCPItemLine(this);   
   cursor.vLine->setPen(pen);
   cursor.vLine->start->setCoords(x, -QCPRange::maxRange);
   cursor.vLine->end->setCoords(x, QCPRange::maxRange);

   //Coordinates as text:   
   if (cursor.cursorText)
      this->removeItem(cursor.cursorText);
   cursor.cursorText = new QCPItemText(this);
   cursor.cursorText->setText(QString("(%1, %2)").arg(x).arg(y));
   cursor.cursorText->position->setCoords(QPointF(x, y));
   QPointF pp = cursor.cursorText->position->pixelPosition() + QPointF(50.0, -15.0);
   cursor.cursorText->position->setPixelPosition(pp);
   cursor.cursorText->setFont(QFont(font().family(), 8));

   //Add to layer:
   if (USING_LAYER){
      cursor.hLine->setLayer(cursorLayer); 
      cursor.vLine->setLayer(cursorLayer); 
      cursor.cursorText->setLayer(cursorLayer);
   }
}

初始化类成员的函数：

void Qt_PlotTest::testPlot(){
   //Create some data and initalize plot:
   QVector<double> yData, xData;
   int imax = 100000;
   for (int i = 0; i < imax; i++){
      double x = double(i) / imax;
      xData.push_back(x);
      yData.push_back(pow(x, 2)*( 1.0 + 0.5*cos(20*x) + 0.1*sin(500*x - 0.1)));
   }
   ui.custom_QWidgetPlot->init(xData, yData);
}

使用图层方法时，光标不会渲染。我尝试了解文档，但我不清楚如何正确使用QCPLayer s。

我该怎么做？

Answer 1

添加图层后

this->addLayer("cursorLayer", 0, QCustomPlot::limAbove);

不要调用QCPLayer构造函数来获取图层指针。使用提供的getter包含图层或索引的名称：

QCPLayer * QCustomPlot::layer ( const QString & name) const

QCPLayer * QCustomPlot::layer ( int index) const

cursorLayer = this->layer("cursorLayer");

此外，每个图表和项目都会添加到currentLayer，在您的情况下，cursorLayer不是main。您需要更改当前图层

bool QCustomPlot::setCurrentLayer ( const QString & name)

bool QCustomPlot::setCurrentLayer ( QCPLayer * layer)

即：

this->setCurrentLayer("cursorLayer");
this->addGraph();
...
this->setCurrentLayer("main");

或者您可以为每个QCPLayerable

指定图层

bool QCPLayerable::setLayer ( QCPLayer * layer)

bool QCPLayerable::setLayer ( const QString & layerName)

someGraph->setLayer("cursorLayer);

Answer 2

正如@EligijusPupeikis提醒我的那样，每次移动光标时我都会删除并重新创建光标。

我认为这不会对我的问题产生任何影响，但显然是这样，因为重新绘制一个包含新项目的图层需要首先重新绘制该图（ source：将检查qcustomplot doc并添加链接）。

所以我的代码现在看起来像这样：

QCustomPlot_custom::QCustomPlot_custom(QWidget* parent)
{
   connect(this, SIGNAL(mouseMove(QMouseEvent*)), this, SLOT(mouseMove(QMouseEvent*)));   
   QCustomPlot::setInteraction(QCP::iRangeDrag, true);
   QCustomPlot::setInteraction(QCP::iRangeZoom, true);
}

void QCustomPlot_custom::init(QVector<double> xdata, QVector<double> ydata)
{   
   this->addGraph();
   this->graph(0)->setData(xdata, ydata);

   QColor colorPen(10, 25, 180, 255);
   QPen pen;
   pen.setWidth(50);
   pen.setColor(colorPen);
   this->graph()->setLineStyle(QCPGraph::lsLine);
   this->graph()->setPen(QPen(colorPen));
   this->xAxis->setLabel("X-axis");
   this->yAxis->setLabel("Y-axis");      
   this->rescaleAxes();
   this->replot();

   if (USING_LAYER){
      this->addLayer("cursorLayer", 0, QCustomPlot::limAbove);
      cursorLayer = this->layer("cursorLayer");
      //cursorLayer = new QCPLayer(this, "cursorLayer");
      cursorLayer->setMode(QCPLayer::lmBuffered);
   }

   //Cursor:
   QPen qpen = QPen(Qt::DashDotLine);
   cursor.hLine = new QCPItemLine(this);
   cursor.hLine->setPen(qpen);
   cursor.vLine = new QCPItemLine(this);
   cursor.vLine->setPen(qpen);
   cursor.cursorText = new QCPItemText(this);
   cursor.cursorText->setFont(QFont(font().family(), 8));

   //Add to layer:
   if (USING_LAYER){
      cursor.hLine->setLayer("cursorLayer");  //"cursorLayer"
      cursor.vLine->setLayer("cursorLayer");
      cursor.cursorText->setLayer("cursorLayer");
   }

}

void QCustomPlot_custom::mouseMove(QMouseEvent* event)
{
   //Cursor coordinates:
   double x = this->xAxis->pixelToCoord(event->pos().x());
   double y = this->yAxis->pixelToCoord(event->pos().y());
   manageCursor(x, y);            
   if (USING_LAYER)
      this->layer("cursorLayer")->replot();
   else
      this->replot();
}

void QCustomPlot_custom::manageCursor(double x, double y)
{
   cursor.hLine->start->setCoords(-QCPRange::maxRange, y);
   cursor.hLine->end->setCoords(QCPRange::maxRange, y);

   cursor.vLine->start->setCoords(x, -QCPRange::maxRange);
   cursor.vLine->end->setCoords(x, QCPRange::maxRange);

   cursor.cursorText->setText(QString("(%1, %2)").arg(x).arg(y));
   cursor.cursorText->position->setCoords(QPointF(x, y));
   QPointF pp = cursor.cursorText->position->pixelPosition() + QPointF(50.0, -15.0);      
 cursor.cursorText->position->setPixelPosition(pp);
}

作为测试，如果我绘制10 000 000个点，并将USING_LAYER设置为false，我会注意到移动鼠标时光标有明显的滞后。将其设置为true时，将导致光标移动平稳。

QCustomPlot重新绘制QCPLayer

2 个答案: