Added crosshair example

examples/crosshair.py

+import initExample ## Add path to library (just for examples; you do not need this)
+import numpy as np
+import pyqtgraph as pg
+from pyqtgraph.Qt import QtGui, QtCore
+from pyqtgraph.Point import Point
+
+#genearte layout
+app = QtGui.QApplication([])
+win = pg.GraphicsWindow()
+label = pg.LabelItem(justify='right')
+win.addItem(label)
+p1 = win.addPlot(row=1, col=0)
+p2 = win.addPlot(row=2, col=0)
+region = pg.LinearRegionItem()
+region.setZValue(10)
+p2.addItem(region)
+
+#create numpy arrays
+#make the numbers large to show that the xrange shows data from 10000 to all the way 0
+data1 = 10000 + 3000 * np.random.random(size=10000)
+data2 = 15000 + 3000 * np.random.random(size=10000)
+
+p1.plot(data1, pen="r")
+p1.plot(data2, pen="g")
+p2.plot(data1, pen="w")
+
+def update():
+    p1.setXRange(*region.getRegion())
+region.sigRegionChanged.connect(update)
+region.setRegion([1000, 2000])
+
+#cross hair
+vLine = pg.InfiniteLine(angle=90, movable=False)
+hLine = pg.InfiniteLine(angle=0, movable=False)
+p1.addItem(vLine, ignoreBounds=True)
+p1.addItem(hLine, ignoreBounds=True)
+vb = p1.vb
+
+def mouseMoved(evt):
+    pos = evt[0]  ## using signal proxy turns original arguments into a tuple
+    if p1.sceneBoundingRect().contains(pos):
+        mousePoint = vb.mapSceneToView(pos)
+        index = int(mousePoint.x())
+        if index > 0 and index < len(data1):
+            label.setText("<span style='font-size: 12pt'>x=%0.1f,   <span style='color: red'>y1=%0.1f</span>,   <span style='color: green'>y2=%0.1f</span>" % (mousePoint.x(), data1[index], data2[index]))
+        vLine.setPos(mousePoint.x())
+        hLine.setPos(mousePoint.y())
+proxy = pg.SignalProxy(p1.scene().sigMouseMoved, rateLimit=60, slot=mouseMoved)
+#p1.scene().sigMouseMoved.connect(mouseMoved)
+
+
+## Start Qt event loop unless running in interactive mode or using pyside.
+import sys
+if (sys.flags.interactive != 1) or not hasattr(QtCore, 'PYQT_VERSION'):
+    app.exec_()
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