Hi,
I think there is a bug somewhere, where the first call to setData() doesn't
result in the view range being updated. Your code is working fine, the plot
is being updated with the correct data, but the axes scales aren't correct
on the first call.
Without spending time tracing through why the ranges aren't being updated,
a simple workaround would be to manually trigger the update by inserting
"self.plot.autoRange()" after your self.spectrum.setData(data) line. Not
ideal, but seems to work.
Patrick
On Tuesday, 18 September 2018 05:54:18 UTC+9:30, GR wrote:
>
>
> Hi,
>
> I am using the following code to generate png files with PyQtGraph.
>
> The code works quite well, but unfortunately, the first loop / picture
> ("0exported_image.png", that is: runner = 0) does not have any data in the
> output picture (respectively: has only default values in the exported
> graph).
> I additionally set a manual breakpoint in "update_data" and looked at the
> attributes of the class instance for runner = 0 and runner >0. It strikes
> that at several parts of the object tree the "picture" is set for runner
> >0, but is not for runner = 0:
>
> "picture": {
> "py/object": "PyQt5.QtGui.QPicture"
> },
>
>
>
> This is the code I use. Does anybody have an idea what could be the reason
> for this?
>
> Thanks in advance.
>
> import numpy as np
> from PyQt5 import QtWidgets
> from PyQt5.QtCore import pyqtSignal, pyqtSlot
> import pyqtgraph as pg
> import pyqtgraph.exporters
> from pyqtgraph.Qt import QtCore, QtGui
> from pyqtgraph import GraphicsLayoutWidget
> from threading import Thread, Event
> import time
>
>
> # Routine to acquire and serve data
> # This might be a camera driver, notifying when a new frame is available
> def generate_data(callback, threadkill):
> # while not threadkill.is_set():
> # width = 1600
> # data = np.zeros(width)
> # runner = int(np.random.random()*5)
> # data.fill(runner)
> # callback(data, runner)
> # time.sleep(0.01)
> for runner in range(5):
> width = 1600
> data = np.zeros(width)
> data.fill(runner)
> my_var = callback(data, runner)
> time.sleep(0.01)
> print("callback called")
>
> # threadkill.set()
> # # sys.exit(1)
>
>
> class PyQtGraphTest(GraphicsLayoutWidget):
> # Signal to indicate new data acquisition
> # Note: signals need to be defined inside a QObject class/subclass
> data_acquired = pyqtSignal(np.ndarray, int)
>
> def __init__(self):
> super().__init__()
> self.exporter = None
>
> self.setWindowTitle('Test pyqtgraph paint signals')
> self.resize(640, 400)
> self.plot = self.addPlot()
> self.spectrum = self.plot.plot()
> self.plot.enableAutoRange(pg.ViewBox.XYAxes)
>
> # Connect the signal
> self.data_acquired.connect(self.update_data)
>
> # Make and start the background thread to acquire data
> # Pass it the signal.emit as the callback function
> self.threadkill = Event()
> self.thread = Thread(target=generate_data,
> args=(self.data_acquired.emit, self.threadkill))
> self.thread.start()
>
> self.thread.join()
> # my_var = self.thread.isAlive()
> # print("my_var:", my_var)
> # self.threadkill.set()
> # print("fin")
>
> # Kill our data acquisition thread when shutting down
> def closeEvent(self, close_event):
> self.threadkill.set()
>
> # Slot to receive acquired data and update plot
> @pyqtSlot(np.ndarray, int)
> def update_data(self, data, runner):
> if not self.exporter:
> # Here we are passing the exporter the GraphicsLayout object that
> is
> # the central item (ci) inside this GraphicsLayoutWidget. That in
> # turn contains the two PlotItem objects.
> self.exporter = pg.exporters.ImageExporter(self.ci)
> self.exporter.parameters()['width'] = 640
>
> self.spectrum.setData(data)
> self.exporter.export(str(runner) + 'exported_image.png')
> print("exported image")
>
>
> if __name__ == '__main__':
> import sys
>
> app = QtWidgets.QApplication(sys.argv)
> window = PyQtGraphTest()
> window.show()
> if (sys.flags.interactive != 1) or not hasattr(QtCore, 'PYQT_VERSION'):
> sys.exit(app.exec_())
>
> print("fin2")
>
>
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