QCustomPlot 重新绘制 QCPLayer

Question

我正在尝试弄清楚如何使用 QCPLayer 仅重新绘制绘图中的某些项目。

qcustomplot documentation 指出：

If you often need to call a full QCustomPlot::replot only because a non-complex object (e.g. an item) has changed while having relatively static but complex graphs in the plot, consider placing the regularly changing objects onto an own layer and setting its mode (QCPLayer::setMode) to QCPLayer::lmBuffered. This makes QCustomPlot allocate a dedicated paint buffer for this layer, and allows it to be replotted individually with QCPLayer::replot, independent of the other layers containing the potentially complex and slow graphs. See the documentation of the respective methods for details.

这就是我在下面的示例中尝试做的事情：

我正在通过继承 QCustomPlot:

创建一个 custom 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 class 使用一些要绘制的数据进行初始化。它还会重载 mouseMove 事件以控制自定义光标。 USING_LAYER 设置为 true 意味着自定义光标被添加到它自己的层 (cursorLayer)。

通过将 USING_LAYER 设置为 false，我得到了如下所示的预期效果：

光标以横竖线和坐标显示。

如果绘图中有很多图 and/or 每个图中有很多点，移动光标时我会看到延迟。（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class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);
}

使用层方法时，光标不呈现。我试着理解文档，但我不清楚如何正确使用 QCPLayers.

我应该怎么做？

Answer 1

添加图层后

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

不要调用 QCPLayer 构造函数来获取层指针。将提供的吸气剂与层或索引的名称一起使用：

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

QCPLayer * QCustomPlot::layer ( int index) const

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

每个图表和项目也被添加到 currentLayer，在您的情况下它不是 cursorLayer，而是 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，我每次移动光标时都会删除 re-creating 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，因为重新绘制其中包含新项目的图层需要先重新绘制绘图（来源：将检查 qcustomplot 文档并添加 link).

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明显滞后。将其设置为 true 时，将导致光标移动平滑。

QCustomPlot 重新绘制 QCPLayer

QCustomPlot replot QCPLayer

c++

qt

qcustomplot