Cheap way to color lots of segments of a PlotDataItem?

[Preston Hinkle]

Hello,

As the title suggests, I'm looking for a way to change the color of discrete segments of a PlotDataItem. My current method creates a PlotDataItem for every segment and plots it over the background with a different pen, but this is apparently very expensive when the number of segments accumulates to around a 1000. Instead, is it possible to draw segments of a single PlotDataItem with different pens? I looked through the documentation but couldn't find anything.

Thanks!

[Luke Campagnola]

PyQtGraph doesn't provide anything like this, but it's pretty easy to write as a QGraphicsItem class. As long as you don't need the data to update rapidly, you can "bake" all of your line segments into a single QPicture. This should be very quick to redraw:

import pyqtgraph as pg

from pyqtgraph.Qt import QtGui, QtCore

import numpy as np

class Segments(QtGui.QGraphicsItem):

    def __init__(self, pos, color):

        QtGui.QGraphicsItem.__init__(self)

        self.pic = QtGui.QPicture()

        painter = QtGui.QPainter()

        painter.begin(self.pic)

        for i in range(len(pos)-1):

            painter.setPen(QtGui.QPen(QtGui.QColor(*color[i])))

            p1 = QtCore.QPointF(*pos[i])

            p2 = QtCore.QPointF(*pos[i+1])

            painter.drawLine(p1, p2)

        painter.end()

    def paint(self, p, *args):

        p.drawPicture(0, 0, self.pic)

    def boundingRect(self):

        return QtCore.QRectF(self.pic.boundingRect())

pos = np.empty((10000,2))

pos[:,0] = np.linspace(0, 10, 10000)

pos[:,1] = np.random.normal(size=(10000))

color = np.random.random(size=(9999,3)) * 255

p = pg.plot()

seg = Segments(pos, color)

p.addItem(seg)

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[Preston Hinkle]

Great, I'll try to implement it.

Thanks! Really loving pyqtgraph btw.

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