Panning Tool

New Feature

QwtPlotPicker is a completely refactored real-time interactive plot picker, providing a more intuitive user experience than the original QwtPlotPicker which implemented panning through caching.

The Qwt6 version of QwtPlotPicker was based on a cache-based panning mechanism, which had two main issues:

• During panning, a cached bitmap was displayed instead of real-time updated plot content
• Users could not see real-time data changes during panning, preventing smooth interactive data exploration

Although in some aspects, the Qwt6 QwtPlotPicker greatly reduced plot refreshes, it was very unfriendly to the visual experience. Therefore, Qwt7 refactored QwtPlotPicker with the goal of achieving smooth interactive data exploration.

Refactored QwtPlotPicker Improvements

The new QwtPlotPicker is based on the QwtPicker state machine mechanism, implementing real-time panning and zooming:

The effect is as follows:

The new QwtPlotPicker provides complete axis support:

• ✅ Linear Scale
• ✅ Logarithmic Scale
• ✅ DateTime Scale
• ✅ Multiple axes

Using the Original Cache-Based Picker

If you want to use the original cache-based picker, you can use QwtPlotCachePicker.

Class Changes	Property	Base Class
QwtPanner -> QwtCachePanner	Renamed	QWidget
Original QwtPlotPanner -> QwtPlotCachePanner	Renamed	QwtCachePanner
Original QwtPolarPanner -> QwtPolarCachePanner	Renamed	QwtCachePanner
QwtPlotPanner	Refactored	QwtPicker

The Qwt6 QwtPlotPanner has been completely refactored, but the interface remains unchanged, so existing code basically requires no modifications.

Basic Usage

#include "qwt_plot_panner.h"
#include "qwt_plot.h"
#include "qwt_plot_curve.h"

// Create plot and curve
QwtPlot* plot = new QwtPlot;
QwtPlotCurve* curve = new QwtPlotCurve("Sine Wave");
curve->attach(plot);

// Create real-time panner
QwtPlotPanner* panner = new QwtPlotPanner(plot->canvas());
// Configure mouse button
panner->setMouseButton(Qt::MiddleButton);  // Middle button panning
// panner->setMouseButton(Qt::LeftButton); // Or left button panning

// Enable picker
panner->setEnabled(true);

// Connect signal (optional)
connect(picker, &QwtPlotPicker::panned,
        [](int dx, int dy) {
            qDebug() << "Canvas panned by:" << dx << dy;
        });

You can set the panning direction to restrict movement to a single direction:

// 1. Set panning direction
panner->setOrientations(Qt::Horizontal | Qt::Vertical); // Default: horizontal and vertical
// panner->setOrientations(Qt::Horizontal);            // Horizontal only
// panner->setOrientations(Qt::Vertical);              // Vertical only

Note

QwtPlotPanner differs from QwtPlotPicker in that it does not need to bind to axes, because the movement applies to the entire canvas. During canvas movement, all axes are moved.