Dynamic matplotlib pyside widget not displaying - matplotlib

Question

I'm writing a python application using pyside and matplotlib. Following a combination of this tutorial and this SO post, I have created a matplotlib widget that I can successfully add to a parent. However when I go to actually add data to it, nothing seems to get displayed.
If I add static data like the SO post had, it shows up, but when I change it to update on the fly (currently every second on a timer, but it will eventually be using a signal from another class), I never get anything but the empty axes to appear. I suspect that I'm missing a call to force a draw or invalidate or that there is something wrong with the way I'm calling update_datalim (though the values that get passed to it seem correct).
from PySide import QtCore, QtGui
import matplotlib
import random
matplotlib.use('Qt4Agg')
matplotlib.rcParams['backend.qt4']='PySide'
from matplotlib import pyplot as plt
from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.figure import Figure
from matplotlib.patches import Rectangle
from collections import namedtuple
DataModel = namedtuple('DataModel', ['start_x', 'start_y', 'width', 'height'])
class BaseWidget(FigureCanvas):
def __init__(self, parent=None, width=5, height=4, dpi=100):
fig = Figure(figsize=(width, height), dpi=dpi)
self.axes = fig.add_subplot(111)
# We want the axes cleared every time plot() is called
self.axes.hold(False)
self.axes.set_xlabel('X Label')
self.axes.set_ylabel('Y Label')
self.axes.set_title('My Data')
FigureCanvas.__init__(self, fig)
self.setParent(parent)
FigureCanvas.setSizePolicy(self,
QtGui.QSizePolicy.Expanding,
QtGui.QSizePolicy.Expanding)
FigureCanvas.updateGeometry(self)
class DynamicWidget(BaseWidget):
def set_data(self, the_data):
self.axes.clear()
xys = list()
cmap = plt.cm.hot
for datum in the_data:
bottom_left = (datum.start_x, datum.start_y)
top_right = (bottom_left[0] + datum.width, bottom_left[1] + datum.height)
rect = Rectangle(
xy=bottom_left,
width=datum.width, height=datum.height, color=cmap(100)
)
xys.append(bottom_left)
xys.append(top_right)
self.axes.add_artist(rect)
self.axes.update_datalim(xys)
self.axes.figure.canvas.draw_idle()
class RandomDataWidget(DynamicWidget):
def __init__(self, *args, **kwargs):
DynamicWidget.__init__(self, *args, **kwargs)
timer = QtCore.QTimer(self)
timer.timeout.connect(self.generate_and_set_data)
timer.start(1000)
def generate_and_set_data(self):
fake_data = [DataModel(
start_x=random.randint(1, 100),
width=random.randint(20, 40),
start_y=random.randint(80, 160),
height=random.randint(20, 90)
) for i in range(100)]
self.set_data(fake_data)
Edit: I'm suspecting that there's an issue with updating the limits of the plot. When running the above code, the plot opens with limits of 0 and 1 on both the x and y axis. Since none of my generated data falls into that range, I created another subclass of DynamicWidget that plots only data between 0 and 1 (the same data from the linked SO post). When instantiating the class below, the data shows up successfully. Do I need to do something more than calling update_datalim to get the graph to re-bound itself?
class StaticWidget(DynamicWidget):
def __init__(self):
DynamicWidget.__init__(self)
static_data = [
DataModel(0.5, 0.05, 0.2, 0.05),
DataModel(0.1, 0.2, 0.7, 0.2),
DataModel(0.3, 0.1, 0.8, 0.1)
]
self.set_data(static_data)

Answer 1

Yes, update_datalim only updates the bounding box that is kept internally by the axes. You also need to enable auto scaling for it to be used. Add self.axes.autoscale(enable=True) after the self.axes.clear() statement and it will work. Or you can set the axes' range to a fixed value by using self.axes.set_xlim and self.axes.set_ylim.
edit: here is my code, which works for me
from PySide import QtCore, QtGui
import matplotlib
import random, sys
matplotlib.use('Qt4Agg')
matplotlib.rcParams['backend.qt4']='PySide'
from matplotlib import pyplot as plt
from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.figure import Figure
from matplotlib.patches import Rectangle
from collections import namedtuple
DataModel = namedtuple('DataModel', ['start_x', 'start_y', 'width', 'height'])
class BaseWidget(FigureCanvas):
def __init__(self, parent=None, width=5, height=4, dpi=100):
fig = Figure(figsize=(width, height), dpi=dpi)
self.axes = fig.add_subplot(111)
# We want the axes cleared every time plot() is called
self.axes.hold(False)
#self.axes.autoscale(enable=True)
self.axes.set_xlabel('X Label')
self.axes.set_ylabel('Y Label')
self.axes.set_title('My Data')
FigureCanvas.__init__(self, fig)
self.setParent(parent)
FigureCanvas.setSizePolicy(self,
QtGui.QSizePolicy.Expanding,
QtGui.QSizePolicy.Expanding)
FigureCanvas.updateGeometry(self)
class DynamicWidget(BaseWidget):
def set_data(self, the_data):
self.axes.clear()
self.axes.autoscale(enable=True)
#self.axes.set_xlim(0, 300)
#self.axes.set_ylim(0, 300)
xys = list()
cmap = plt.cm.hot
for datum in the_data:
print datum
bottom_left = (datum.start_x, datum.start_y)
top_right = (bottom_left[0] + datum.width, bottom_left[1] + datum.height)
rect = Rectangle(
xy=bottom_left,
width=datum.width, height=datum.height, color=cmap(100)
)
xys.append(bottom_left)
xys.append(top_right)
self.axes.add_artist(rect)
self.axes.update_datalim(xys)
self.axes.figure.canvas.draw_idle()
class RandomDataWidget(DynamicWidget):
def __init__(self, *args, **kwargs):
DynamicWidget.__init__(self, *args, **kwargs)
timer = QtCore.QTimer(self)
timer.timeout.connect(self.generate_and_set_data)
timer.start(1000)
def generate_and_set_data(self):
fake_data = [DataModel(
start_x=random.randint(1, 100),
width=random.randint(20, 40),
start_y=random.randint(80, 160),
height=random.randint(20, 90)) for i in range(100)]
self.set_data(fake_data)
print "done:...\n\n"
def main():
qApp = QtGui.QApplication(sys.argv)
aw = RandomDataWidget()
aw.show()
aw.raise_()
sys.exit(qApp.exec_())
if __name__ == "__main__":
main()