QCustomPlot Scale Bar Component

ScaleBar.cc

#include "ScaleBar.h"

ScaleBar::ScaleBar(QCustomPlot *plot)
    : QObject{plot},
      mPlot(plot)
{
    mScaleBar = new QCPItemLine(mPlot);

    QPen p(Qt::NoBrush, 1.5F);
    p.setColor(Qt::red);
    mScaleBar->setPen(p);
    mScaleBar->setHead(QCPLineEnding::esBar);
    mScaleBar->setTail(QCPLineEnding::esBar);
    mScaleBar->setLayer("overlay");

    mScaleLabel = new QCPItemText(mPlot);
    mScaleLabel->setTextAlignment(Qt::AlignCenter);
    mScaleLabel->setColor(Qt::red);
    mScaleLabel->setText(tr("10 um"));
    mScaleLabel->position->setType(QCPItemPosition::ptAbsolute);

    connect(mPlot, &QCustomPlot::beforeReplot, this, &ScaleBar::onBeforePlot);
}

void ScaleBar::setVisible(bool visible)
{
    mScaleBar->setVisible(visible);
    mScaleLabel->setVisible(visible);
    mPlot->replot(QCustomPlot::rpQueuedReplot);
}

const bool ScaleBar::visible() const
{
    return mVisible;
}

void ScaleBar::setScale(uint32_t scale)
{
    if (scale > 0) {
        mScale = scale;
        mPlot->replot(QCustomPlot::rpQueuedReplot);
    }
}

uint32_t ScaleBar::scale() const
{
    return mScale;
}

void ScaleBar::updateScaleBar()
{
    if (!mVisible) {
        return;
    }
    const QPoint btLeft = mPlot->xAxis->axisRect()->bottomLeft();
    const QPoint btRight = mPlot->xAxis->axisRect()->bottomRight();
    const QPoint tpLeft = mPlot->xAxis->axisRect()->topLeft();

    const int x = btRight.x() - btLeft.x();
    const int y = btLeft.y() - tpLeft.y();
    mScaleBar->start->setType(QCPItemPosition::ptAbsolute);
    mScaleBar->end->setType(QCPItemPosition::ptAbsolute);
    const double range = mScale;
    QPointF start = QPointF(btLeft) + QPointF(x * 0.05, -y * 0.05);
    QPointF coordStart = QPointF(mPlot->xAxis->pixelToCoord(start.x()), mPlot->yAxis->pixelToCoord(start.y()));
    QPointF coordEnd = coordStart + QPointF(range, 0);
    const int sx = start.x();
    const int sy = start.y();
    const int ex = mPlot->xAxis->coordToPixel(coordEnd.x());
    const int ey = mPlot->yAxis->coordToPixel(coordEnd.y());

    mScaleBar->start->setPixelPosition(start);
    mScaleBar->end->setPixelPosition(QPoint(ex, start.y()));

    mScaleLabel->setText(tr("%1 um").arg(QString::number(mScale)));
    QFontMetrics metric(mScaleLabel->font());
    mScaleLabel->position->setPixelPosition(QPoint((ex + sx) / 2, ey - metric.height() / 2 - 2));
}

void ScaleBar::onBeforePlot()
{
    updateScaleBar();
}

ScaleBar.h

#ifndef SCALEBAR_H
#define SCALEBAR_H

#include <QObject>
#include "qcustomplot.h"

class ScaleBar : public QObject
{
    Q_OBJECT
public:
    explicit ScaleBar(QCustomPlot *plot);

    void setVisible(bool visible);
    const bool visible() const;

    void setScale(uint32_t scale);
    uint32_t scale() const;

Q_SIGNALS:

private:
    QCustomPlot* mPlot{nullptr};
    QCPItemLine* mScaleBar{nullptr};
    QCPItemText* mScaleLabel{nullptr};
    bool mVisible{true};
    uint32_t mScale{10};

    void updateScaleBar();

private Q_SLOTS:
    void onBeforePlot();

};

#endif // SCALEBAR_H