【发布时间】：2018-02-26 16:33:22
【问题描述】：
我有一个包含许多 QwtPlotCurve 的 QwtPlot 视图，我想突出显示/放大（目前只是尝试更改颜色）离鼠标位置最近的点（因为我将显示一些关于这一点的信息用户按下鼠标按钮时的测量值，我想让他知道当前的“目标”是什么点）。
所以我使用QwtPlotPicker 来获取鼠标位置，然后我设置了一个额外的QwtPlotCurve 曲线，这个单点（“目标”）在其他点之上用不同的颜色绘制。
它可以工作，但我可以完成这项工作的唯一方法是调用QwtPlot::replot()，每次移动鼠标时都要调用它（因为我可能要绘制数千个点）。
我只想重绘之前高亮点所在的区域（以恢复默认显示），然后只重绘新高亮点所在的区域。但是当我这样做时，这个（调用repaint(QRect)而不是replot()），什么也没有发生（没有突出显示点），但是，如果我停用窗口，我看到该点被突出显示，所以看起来repaint确实一些工作，但不足以让最终用户看到它......
请注意，我禁用了 Qwt 后备存储功能。
这是我的 MCVE：
widget.h:
#include <QDialog>
class QLabel;
class QwtPlotCurve;
class QwtPlot;
class Dialog : public QDialog
{
Q_OBJECT
public:
Dialog();
public slots:
void onHovered( const QPointF& pt );
private:
std::vector<QwtPlotCurve*> curves;
QwtPlotCurve* highlight;
std::tuple<QwtPlotCurve*,int,QRect> highlighted;
QLabel* closestLabel;
QwtPlot* plot;
};
widget.cpp：
#include "widget.h"
#include <QVBoxLayout>
#include <QLabel>
#include <qwt_plot.h>
#include <qwt_plot_curve.h>
#include <qwt_plot_picker.h>
#include <qwt_plot_canvas.h>
#include <qwt_picker_machine.h>
#include <sstream>
Dialog::Dialog()
{
setLayout( new QVBoxLayout() );
plot = new QwtPlot(this);
layout()->addWidget( plot );
layout()->addWidget( closestLabel = new QLabel( this ) );
for ( int i = 0; i != 5; ++i )
{
QwtPlotCurve* curve = new QwtPlotCurve();
QVector<double> x, y;
for ( int i = 0; i != 10; ++i )
{
x.push_back( std::rand() );
y.push_back( std::rand() );
}
curve->setSamples( x, y );
curve->setStyle( QwtPlotCurve::Dots );
curve->setPen( Qt::black, 5 );
curve->attach(plot);
curves.push_back( curve );
}
highlight = new QwtPlotCurve();
highlight->setSamples( {}, {} );
highlight->setStyle( QwtPlotCurve::Dots );
highlight->setPen( Qt::red, 5 );
highlight->attach(plot);
QwtPlotCanvas* canvas = dynamic_cast<QwtPlotCanvas*>( plot->canvas() );
if ( canvas )
canvas->setPaintAttribute( QwtPlotCanvas::BackingStore, false );
plot->replot();
QwtPlotPicker* picker = new QwtPlotPicker( plot->canvas() );
picker->setStateMachine(new QwtPickerTrackerMachine());
connect(picker, SIGNAL(moved(const QPointF&)), this, SLOT(onHovered(const QPointF&)));
}
// inspired from QwtPlotCurve::closestPoint
int closestPoint( QwtPlotCurve& curve, const QPoint &pos, double *dist )
{
const size_t numSamples = curve.dataSize();
if ( curve.plot() == NULL || numSamples <= 0 )
return -1;
const QwtSeriesData<QPointF> *series = curve.data();
const QwtScaleMap xMap = curve.plot()->canvasMap( curve.xAxis() );
const QwtScaleMap yMap = curve.plot()->canvasMap( curve.yAxis() );
const double xPos = xMap.transform( pos.x() );
const double yPos = yMap.transform( pos.y() );
int index = -1;
double dmin = DBL_MAX;
for ( uint i = 0; i < numSamples; i++ )
{
const QPointF sample = series->sample( i );
const double cx = xMap.transform( sample.x() ) - xPos;
const double cy = yMap.transform( sample.y() ) - yPos;
const double dist = sqrt( pow(cx,2) + pow(cy,2) );
if ( dist < dmin )
{
index = i;
dmin = dist;
}
}
if ( dist )
*dist = dmin;
return index;
}
void Dialog::onHovered( const QPointF& pt )
{
// mouse moved!
QwtPlotCurve* closest = NULL;
int closestIndex = -1;
double minDist = DBL_MAX;
for ( auto curve : curves )
{
double dist;
int index = closestPoint( *curve, pt.toPoint(), &dist );
if ( dist < minDist )
{
minDist = dist;
closestIndex = index;
closest = curve;
}
}
if ( !closest )
return;
std::stringstream str;
QPointF closestPoint = closest->sample(closestIndex);
str << "Closest point is " << closestPoint.rx() << "," << closestPoint.ry();
closestLabel->setText( str.str().c_str() );
if ( std::get<0>( highlighted ) == closest &&
std::get<1>( highlighted ) == closestIndex )
{
// highlighted point is unchanged
return;
}
else
{
// highlighted point changed
const QwtScaleMap xMap = plot->canvasMap( QwtPlot::xBottom );
const QwtScaleMap yMap = plot->canvasMap( QwtPlot::yLeft );
const int rectSize = highlight->pen().width() * 2;
const int x = xMap.transform( closestPoint.rx() );
const int y = xMap.transform( closestPoint.ry() );
const QRect cr = plot->canvas()->contentsRect();
highlight->setSamples( { closestPoint.rx() }, { closestPoint.ry() } );
QRect smallCR( x - rectSize/2, y - rectSize/2, rectSize, rectSize );
std::tuple<QwtPlotCurve*,int,QRect> newHighlighted{ closest, closestIndex, smallCR };
QwtPlotCanvas* canvas = dynamic_cast<QwtPlotCanvas*>( plot->canvas() );
if ( canvas )
{
if ( std::get<2>( highlighted ) != QRect() )
{
// repaint previously highlighted area:
canvas->repaint( std::get<2>( highlighted ) );
}
// repaint newly highlighted area:
canvas->repaint( std::get<2>( newHighlighted ) );
// if you replace lines above by this one, it works!
//canvas->replot();
}
highlighted = newHighlighted;
}
}
main.cpp:
#include <QApplication>
#include "widget.h"
int main( int argc, char* argv[] )
{
QApplication app( argc, argv );
Dialog dlg;
dlg.show();
return app.exec();
}
编辑：
如果我将highlight = new QwtPlotCurve(); 替换为highlight = new MyCurve(); 与MyCurve 定义为：
class MyCurve : public QwtPlotCurve
{
public:
void drawSeries( QPainter *painter,
const QwtScaleMap &xMap, const QwtScaleMap &yMap,
const QRectF &canvasRect, int from, int to ) const override
{
static int i = 0;
if ( dataSize() != 0 )
std::cout << "PAINTING " << i++ << std::endl;
QwtPlotCurve::drawSeries( painter, xMap, yMap, canvasRect, from, to );
}
};
然后我看到控制台在调用每个canvas->repaint 时显示一个新的“PAINTING”，但是红点不可见。现在，如果我将另一个窗口移到我的上方（或按 Alt），则会报告一个新的“PAINTING”，这次最近的点变为红色。正如我所提到的，该方法看起来不错，但不足以让视图按预期重新绘制......
【问题讨论】：