Pan chart using mouse - Jfreechart

Question

Can we implement the pan functionality as a mouse drag event in JfreeChart? Right now I press CTRL and drag my mouse to pan a chart. I want to implement the pan functionality just by dragging the mouse. Is that possible ?

Eric Leibenguth Eric Leibenguth · Accepted Answer · 2015-07-05T12:41:56

It is apparently impossible to change the modifier key with the current JFreeChart API, as discussed here (but it is in the pipeline).

However, everything is there to pan a chart programmatically, so you could try the following:

Add a MouseMotionListener to your ChartPanel to track mouseDragged() events.
From these events, compute the requested movement of the chart.
Call directly XYPlot.panDomainAxes() and XYPlot.panRangeAxis() (API here).

Take inspiration from ChartPanel source code:

/** 
 * Temporary storage for the width and height of the chart 
 * drawing area during panning.
 */
private double panW, panH;

/** The last mouse position during panning. */
private Point panLast;

/**
 * The mask for mouse events to trigger panning.
 *
 * @since 1.0.13
 */
private int panMask = InputEvent.CTRL_MASK;

...

/**
 * Handles a 'mouse pressed' event.
 * <P>
 * This event is the popup trigger on Unix/Linux.  For Windows, the popup
 * trigger is the 'mouse released' event.
 *
 * @param e  The mouse event.
 */
@Override
public void mousePressed(MouseEvent e) {
    if (this.chart == null) {
        return;
    }
    Plot plot = this.chart.getPlot();
    int mods = e.getModifiers();
    if ((mods & this.panMask) == this.panMask) {
        // can we pan this plot?
        if (plot instanceof Pannable) {
            Pannable pannable = (Pannable) plot;
            if (pannable.isDomainPannable() || pannable.isRangePannable()) {
                Rectangle2D screenDataArea = getScreenDataArea(e.getX(),
                        e.getY());
                if (screenDataArea != null && screenDataArea.contains(
                        e.getPoint())) {
                    this.panW = screenDataArea.getWidth();
                    this.panH = screenDataArea.getHeight();
                    this.panLast = e.getPoint();
                    setCursor(Cursor.getPredefinedCursor(
                            Cursor.MOVE_CURSOR));
                }
            }
            // the actual panning occurs later in the mouseDragged() 
            // method
        }
    }
    else if (this.zoomRectangle == null) {
        ...
    }
}

...

/**
 * Handles a 'mouse dragged' event.
 *
 * @param e  the mouse event.
 */
@Override
public void mouseDragged(MouseEvent e) {

    // if the popup menu has already been triggered, then ignore dragging...
    if (this.popup != null && this.popup.isShowing()) {
        return;
    }

    // handle panning if we have a start point
    if (this.panLast != null) {
        double dx = e.getX() - this.panLast.getX();
        double dy = e.getY() - this.panLast.getY();
        if (dx == 0.0 && dy == 0.0) {
            return;
        }
        double wPercent = -dx / this.panW;
        double hPercent = dy / this.panH;
        boolean old = this.chart.getPlot().isNotify();
        this.chart.getPlot().setNotify(false);
        Pannable p = (Pannable) this.chart.getPlot();
        if (p.getOrientation() == PlotOrientation.VERTICAL) {
            p.panDomainAxes(wPercent, this.info.getPlotInfo(),
                    this.panLast);
            p.panRangeAxes(hPercent, this.info.getPlotInfo(),
                    this.panLast);
        }
        else {
            p.panDomainAxes(hPercent, this.info.getPlotInfo(),
                    this.panLast);
            p.panRangeAxes(wPercent, this.info.getPlotInfo(),
                    this.panLast);
        }
        this.panLast = e.getPoint();
        this.chart.getPlot().setNotify(old);
        return;
    }

    ...

}

...

/**
 * Handles a 'mouse released' event.  On Windows, we need to check if this
 * is a popup trigger, but only if we haven't already been tracking a zoom
 * rectangle.
 *
 * @param e  information about the event.
 */
@Override
public void mouseReleased(MouseEvent e) {

    // if we've been panning, we need to reset now that the mouse is 
    // released...
    if (this.panLast != null) {
        this.panLast = null;
        setCursor(Cursor.getDefaultCursor());
    }

    ...

}

EDIT: Noticing that the only problem with the current API is that panMask is private, why don't you try to hack the field with reflection:

Field mask = ChartPanel.class.getDeclaredField("panMask");
mask.setAccessible(true);
mask.set(yourChartPanel, Integer.valueOf(0)); // The "0" mask is equivalent to no mask. You could also set a different modifier.

Pan chart using mouse - Jfreechart

3 Answers