pyQtGraph detect widget bounds and start scrolling - arrays

Question

I'm trying to plot a live graph (a graph about the evolution of a stock trading) with pyQtGraph and have some questions I haven't been able to solve checking the examples:
I want the graph to start painting from left to right (this is what happens by default) and when it reaches right side of bounding box instead of resize it to make all new data fit I would like it to scroll making new data enter from the right and old data dissapearing to the left.
I know that appending data to a numpy array creates a new instance of the array. I don't want this. Is there any way to tell pyQtGraph plot to just get data in a range of the numpy array? For exmaple could I instantiate initially an array of 10000 floats and tell pyQtGraph to just plot the first 100 floats?
On the other hand I have come across that I could just modify the array in-place and shift the numbers to simulate the scrolling. Is there any way to make pyQtGraph use a numpy array as a ring? This way I would only need to tell that the graph starts at an index and everything would work without allocations, etc...
Here the code I have so far, pretty simple:
class Grapher(QtWidgets.QMainWindow, Ui_MainWindow):
def __init__(self):
QtWidgets.QMainWindow.__init__(self)
Ui_MainWindow.__init__(self)
self.setupUi(self)
self.graphicsView.setTitle('My Graph')
self.graphicsView.setLabel('bottom', 'X axis')
self.graphicsView.setLabel('left', 'Y axis')
self.graphicsView.setLimits(xMin=0, yMin=0)
self.graphicsView.showGrid(x=True, y=True)
self.x=np.array();
self.y=np.array();
self._timer=QtCore.QTimer()
self._timer.timeout.connect(self.update)
self._timer.start(1000)
self._timerCounter=0;
def update(self):
self.x=np.append(self.x, [self._timerCounter]);
self.y=np.append(self.y, [math.sin(self._timerCounter)])
self.graphicsView.plot(self.x, self.y)
self._timerCounter+=1;
Thanks in advance.

Answer 1

This is how I would do it. If, say, you have an array of 1000 points but you only want to plot 200 points:
class Grapher(QtWidgets.QMainWindow, Ui_MainWindow):
def __init__(self):
QtWidgets.QMainWindow.__init__(self)
Ui_MainWindow.__init__(self)
self.setupUi(self)
self.graphicsView.setTitle('My Graph')
self.graphicsView.setLabel('bottom', 'X axis')
self.graphicsView.setLabel('left', 'Y axis')
self.graphicsView.setLimits(xMin=0, yMin=0)
self.graphicsView.showGrid(x=True, y=True)
self.plot = self.graphicsView.plot()
self.ptr = 0
self.x = np.zeros(1000)
self.y = np.zeros(1000)
self.xPlot = np.zeros(200)
self.yPlot = np.zeros(200)
self._timer = QtCore.QTimer()
self._timer.timeout.connect(self.update)
self._timer.start(1000)
self._timerCounter = 0
def update(self):
xNew = self._timerCounter
yNew = math.sin(xNew)
self.y[self.ptr] = math.sin(self._timerCounter)
self.x[self.ptr] = self._timerCounter
if self.ptr < 200:
# Normal assignment
self.yPlot[self.ptr] = self.y[self.ptr]
self.xPlot[self.ptr] = self.x[self.ptr]
self.plot.setData(self.xPlot[1:self.ptr + 1],
self.yPlot[1:self.ptr + 1])
else:
# Shift arrays and then assign
self.yPlot[:-1] = self.yPlot[1:]
self.yPlot[-1] = self.y[self.ptr]
self.xPlot[:-1] = self.xPlot[1:]
self.xPlot[-1] = self.x[self.ptr]
self.plot.setData(self.xPlot, self.yPlot)
self.ptr += 1