PyQtGraph PolyLineROI maxBounds Not Working

Question

I have a PolyLineROI in a PlotItem and am trying to limit the handles to moving only within the bounds of the plot. I have tried to use the maxBounds argument, but this does not work (the handles still move outside the graph):

Code:

import pyqtgraph as pg
from pyqtgraph.Qt import QtCore

app = pg.mkQApp('Plot')

window = pg.GraphicsLayoutWidget(show=True, size=(400,400), border=False, title='Plot')
plt = window.addPlot(title='Plot')

polyline = pg.PolyLineROI(
    [[0,0], [10,10], [10,30], [30,10]],
    closed=False,
    maxBounds=QtCore.QRectF(0,0,30,30)
)

plt.addItem(polyline)

plt.disableAutoRange('xy')
plt.autoRange()

if __name__ == "__main__":
    pg.exec()

Problem:

I have seen this question asked on these mailing lists:

1. Google Group
2. Mail Archive Google Group

but they don't have any answers and this has not been asked here.

How can I prevent the handles from moving outside the bounds of the graph?

Answer 1

To do this, you must subclass PolyLineROI and override checkPointMove:

Code:

import pyqtgraph as pg
from pyqtgraph.Qt import QtCore

class GraphPolyLine(pg.PolyLineROI):

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

    def checkPointMove(self, handle, pos, modifiers):
        if self.maxBounds is not None:
            pt = self.getViewBox().mapSceneToView(pos)
        
            if not self.maxBounds.contains(pt.x(), pt.y()):
                return False

        return True

app = pg.mkQApp("ROI Examples")

window = pg.GraphicsLayoutWidget(show=True, size=(400,400), border=False, title='Plot')

plt = window.addPlot(title="Plot")
plt.setMouseEnabled(False, False)  # Disable zoom and pan

polyline = GraphPolyLine(
    [[0,0], [10,10], [10,30], [30,10]],
    closed=False,
    maxBounds = QtCore.QRectF(0, 0, 30, 30)
)

plt.addItem(polyline)
plt.disableAutoRange('xy')
plt.autoRange()

if __name__ == "__main__":
    pg.exec()

Solution:

From pyqtgraph.graphicsItems.ROI, we see