Scrolling plots: when symbol arg is passed to plot(), scrolling left does not work

[Mark]

Hi Luke - 

Thanks for all your work in pyqtgraph.

I'm using 0.10.0 with PyQT 5.7 on Windows 7.

I have built a scrolling chart that loads data from a pandas dataframe that is populated from another process. It creates PlotDataItems with 500 data points each. Then applies np.empty() to the numpy array it and loads it again with new data, etc.

I have found that when I add a 'symbol' argument to the plot() method (see below), the previous PlotDataItems do not get shifted left during the shift process. However, the current PlotDataItem shifts to the left, correctly, in this situation. (See the attached screenshot: 'top_symbol_curve_does_not_shift_left.PNG' - you'll note lime green lines at the left of the screenshot where the top symbol-based plotdataitems get out of sync with the 'white line' plotdataitem.

However, when I take out the symbol argument, the second line scrolls to the left perfectly (as you probably know - this a modification from one of your samples). See 'both_curves_shift_left.PNG' screenshot for how this works correctly.

<SNIPPET>

       for index,row in pandas_df.iterrows():

            move_value = move_position(0.15) # THIS IS A CALL TO A FUNCTION THAT GENERATES AN INCREMENTED VALUE INSTEAD OF USING NOW() TIMESTAMP

            shift = (move_value * -1)

            for c in curves:

                c.setPos(shift, 0) # moves the curve

            for c2 in curves2:

                c2.setPos(shift,0)

            i = ptr5 % 500

            if i==0:

                curve = p5.plot()

                curves.append(curve)

                curve2 = p5.plot(pen=(32,178,170))  #<- WORKS FINE

                #curve2 = p5.plot(pen=None,symbol='d', symbolBrush=(32,178,170)) <- ONLY THE CURRENT PLOTDATA ITEM SHIFTS. PREVIOUS ONES DO NOT

                curves2.append(curve2)

               

                last = data5[-1] #return last item in the list 

                last2 = pyqt_dot_np[-1]

                data5 = np.empty([501,2]) #Return a new array of given shape and type, without initializing entries.

                pyqt_dot_np = np.empty([501,2])

                data5[0] = last

                pyqt_dot_np[0] = last2

            else:

               curve = curves[-1] #return last item in the list

               curve2 = curves2[-1]

            vb = curve.getViewBox()

            xrange = vb.viewRange()[0]  

            data5[i+1,0] = move_value

            pyqt_dot_np[i+1,0] = move_value

            data5[i+1,1] = row['Zscores'] # 2-D array - y values

            curve.setData(x=data5[:i+2, 0], y=data5[:i+2, 1])

            pyqt_dot_np[i+1,1] = row['Zscores'] + 0.5

            curve2.setData(x=pyqt_dot_np[:i+2, 0], y=pyqt_dot_np[:i+2, 1])

</SNIPPET>

Is this a bug?

Do I need to do something differently to scroll previously added symbol objects. 

Thanks kindly,

Mark

[Luke Campagnola]

It's a bug! Would you mind opening a new issue on github?

Here's a workaround:

    curve.scatter.updateSpots()

    curve.scene().update()

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[Mark]

Thanks Luke and thanks for the work-around.

I will post a new issue this weekend.

Mark

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[Mark]

Luke - the work-around fixed it.

Thanks!