qcodes.plots.pyqtgraph.QtPlot.update_plot() not compatible with pyqtgraph==0.13.1

[Robert Sokolewicz]

I'm one of the developers of quantify and our package heavily depends on qcodes. The latest pyqtgraph release (0.13.1) brought a few changes that we needed to address and unfortunately one issue actually stems from within qcodes.

I don't have nice minimal working example, but I think the issue should be clear. We have a PlotMonitor class that launches multiple instances of QtPlot which right after running update_plot raises an AttributeError with the following traceback

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/quantify-quantify-core/envs/382/lib/python3.8/site-packages/quantify_core/visualization/pyqt_plotmon_remote.py", line 158, in _exec_queue
    getattr(self, attr_name)(*args)
  File "/home/docs/checkouts/readthedocs.org/user_builds/quantify-quantify-core/envs/382/lib/python3.8/site-packages/quantify_core/visualization/pyqt_plotmon_remote.py", line 664, in update
    self.secondary_QtPlot.update_plot()
  File "/home/docs/checkouts/readthedocs.org/user_builds/quantify-quantify-core/envs/382/lib/python3.8/site-packages/qcodes/plots/pyqtgraph.py", line 468, in update_plot
    self._update_image(plot_object, config)
  File "/home/docs/checkouts/readthedocs.org/user_builds/quantify-quantify-core/envs/382/lib/python3.8/site-packages/qcodes/plots/pyqtgraph.py", line 307, in _update_image
    img.translate(scales['x'].translate, scales['y'].translate)
AttributeError: 'ImageItem' object has no attribute 'translate'

(secondary_QtPlot is assigned to an instance of QtPlot)

Looking at the documentation of pyqtgraph, the "new" way of applying transforms is via QtGui.QTransform(). The example they give is

tr = QtGui.QTransform()  # prepare ImageItem transformation:
tr.scale(6.0, 3.0)       # scale horizontal and vertical axes
tr.translate(-1.5, -1.5) # move 3x3 image to locate center at axis origin

img = pg.ImageItem( image=np.eye(3), levels=(0,1) ) # create example image
img.setTransform(tr) # assign transform

I think the issue is resolved when we replace all lines containing img.translate and img.scale with img.setTransform.

The issue arose with qcodes==0.33.0 and pyqtgraph==0.13.1.

[Jens Hedegaard Nielsen]

@rsokolewicz thanks for reaching out. Honestly that code sees very little use for us internally. I am happy to merge a pr that fixes this but it might take a bit of time before we get to it otherwise