[vtkusers] Problem with vtkPiecewiseFunction (0x1c4d430): Index out of range! (test case included)

[Elvis Stansvik]

Hi all,

I'd like to use a vtkCompositeTransferFunctionItem +
vtkCompositeControlPointsItem combo inside a vtkChartXY, for editing a
color transfer function (and visualizing the opacity transfer function at
the same time).

I want to use
SetPointsFunction(vtkCompositeControlPointsItem.ColorPointsFunction) on the
vtkCompositeControlPointsItem, to enable editing only of the color transfer
function (while still showing the opacity transfer function). But if I do
so, I get a

ERROR: In
/build/vtk7-0qbNHX/vtk7-7.0.0/Common/DataModel/vtkPiecewiseFunction.cxx,
line 349
vtkPiecewiseFunction (0x277bc50): Index out of range!

when I double a certain point in the plot to edit it.

Here's a minimal test case:

from vtk import vtkRenderWindow
from vtk import vtkRenderWindowInteractor
from vtk import vtkColorTransferFunction
from vtk import vtkPiecewiseFunction
from vtk import vtkContextView
from vtk import vtkChartXY
from vtk import vtkAxis
from vtk import vtkCompositeTransferFunctionItem
from vtk import vtkCompositeControlPointsItem
from vtk import vtkControlPointsItem

# Create a render window and interactor
renderWindow = vtkRenderWindow()
interactor = vtkRenderWindowInteractor()

# Create a color transfer function
colorFunction = vtkColorTransferFunction()
colorFunction.AddHSVSegment(0., 0., 1., 1., 1./3, 1./3, 1., 1.)
colorFunction.AddHSVSegment(1./3, 1./3, 1., 1., 2./3, 2./3, 1., 1.)
colorFunction.AddHSVSegment(2./3, 2./3, 1., 1., 1., 0., 1., 1.)

# Create an opacity transfer function
opacityFunction = vtkPiecewiseFunction()
opacityFunction.AddPoint(0.2, 0.)
opacityFunction.AddPoint(0.5, 0.5)
opacityFunction.AddPoint(1., 1.)

# Create an item for showing the transfer functions
functionsItem = vtkCompositeTransferFunctionItem()
functionsItem.SetColorTransferFunction(colorFunction)
functionsItem.SetOpacityFunction(opacityFunction)
functionsItem.SetMaskAboveCurve(True)

# Create an item for showing/controlling the color
# transfer function points
pointsItem = vtkCompositeControlPointsItem()
pointsItem.SetPointsFunction(
    vtkCompositeControlPointsItem.ColorPointsFunction)
pointsItem.SetColorTransferFunction(colorFunction)
pointsItem.SetOpacityFunction(opacityFunction)
pointsItem.SetUseOpacityPointHandles(True)
pointsItem.SetEndPointsXMovable(False)
pointsItem.SetEndPointsRemovable(False)
pointsItem.SetShowLabels(True)
pointsItem.SetLabelFormat("%.3f : %.3f")

def editPoint(sender, event):
    print('TODO: edit point')

pointsItem.AddObserver(
    vtkControlPointsItem.CurrentPointEditEvent, editPoint)

# Create an XY chart to hold the items
chart = vtkChartXY()
chart.AddPlot(functionsItem)
chart.AddPlot(pointsItem)

# Create a context view to show the chart
view = vtkContextView()
view.GetScene().AddItem(chart)
view.SetRenderWindow(renderWindow)
view.SetInteractor(interactor)

interactor.Start()

Launch the program and then double click the third point. You will get

TODO: edit point
ERROR: In
/build/vtk7-0qbNHX/vtk7-7.0.0/Common/DataModel/vtkPiecewiseFunction.cxx,
line 349
vtkPiecewiseFunction (0x1c4d430): Index out of range!

printed. The first printout ("TODO: edit point") is from my editPoint(...)
function, while the ERROR message comes from inside VTK. After having made
the first double click these error messages keeps spewing on the console as
soon as you move the mouse over the chart. This only happens when
doubleclicking the third point (at index 2), not when doubleclicking point
0, 1 or 3.

Anyone know what is going on? I also noticed that if I remove the line

pointsItem.SetPointsFunction(
    vtkCompositeControlPointsItem.ColorPointsFunction)

The problem disappears. But this will not give me the kind of editor I want.

Elvis
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