PyQtGraph's coordinate system is inherited from Qt's GraphicsView (
http://doc.qt.io/qt-4.8/graphicsview.html). Basically, it uses a scenegraph
where each item in the scene is assigned a 2D matrix transform, and the
final transform used to draw each item is generated on-demand by
multiplying the item's transform with the transforms of its parents. This
system is efficient but not very flexible (and it's maybe the thing I
dislike the most about using Qt GraphicsView).
So the PyQtGraph equivalent just involves manually updating the position of
each curve whenever the view range has changed:
import pyqtgraph as pg
import numpy as np
plt = pg.plot()
curves = [plt.plot(np.random.normal(size=100)) for i in range(5)]
# Don't try to scale the y-axis automatically
plt.enableAutoRange(x=True, y=False)
plt.setYRange(-30, 30)
def updateCurves():
# Set a good y position for each curve
vb = plt.plotItem.vb
height = vb.height()
for i,curve in enumerate(curves):
y = vb.mapToView(pg.Point(0, (i+1) * height / (len(curves)+1))).y()
curve.setPos(0, y)
plt.plotItem.vb.sigRangeChanged.connect(updateCurves)
updateCurves()
Luke
On Wed, Nov 8, 2017 at 9:44 AM, Brad Buran <[email protected]> wrote:
> I'm updating some code that was written in Chaco to use PyQtGraph instead.
> I'm working with relatively low-level primitives from PyQtGraph to maximize
> my control over the various components. For example, I am creating a
> GraphicsLayout, inserting a ViewBox and then adding the PlotCurveItem to
> the ViewBox.
>
> One thing I would like to accomplish in a single ViewBox is to have
> multiple PlotCurveItems. However, each curve needs to be offset vertically
> relative to the axes coordinates. For example, if I have three plots, the
> plots would be spaced equally along the vertical axis. However, when I use
> the mouse wheel to scale the Y-axis, it should scale the plot (but not the
> position of the plot).
>
> This is easy to accomplish in Matplotlib using their transform system. For
> example, I would do:
>
> import matplotlib as mp
> import pylab as pl
> import numpy as np
>
> ax = pl.gca()
>
> x = np.arange(100)
> y = np.random.uniform(-1, 1, size=100)
>
> offset_transform = mp.transforms.Affine2D().translate(0, 0.25)
> new_transform = ax.transLimits + offset_transform + ax.transAxes
> ax.plot(x, y, 'ro-', transform=new_transform)
>
> offset_transform = mp.transforms.Affine2D().translate(0, 0.5)
> new_transform = ax.transLimits + offset_transform + ax.transAxes
> ax.plot(x, y, 'go-', transform=new_transform)
>
> offset_transform = mp.transforms.Affine2D().translate(0, 0.75)
> new_transform = ax.transLimits + offset_transform + ax.transAxes
> ax.plot(x, y, 'bo-', transform=new_transform)
>
> #ax.axis(ymin=0, ymax=5)
> pl.show()
>
> Does PyQtGraph have a similar system?
>
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