[vtkusers] How to put vtkImagePlaneWidget behind actors ?

Istvan Matis i_matis at yahoo.de
Wed Aug 9 14:46:11 EDT 2006

Hello Charl and Dean,

thanks for the comments.

I tried out PassAlphaToOutputOff and it seems to work. 
Unfortunately I also use transparent colors in the LUT of the IPW in order
to "cut" the image data outside the region of interest, which is fully
transparent, and leaving only the ROI with full opacity.
But anyway it is good for a short term solution.

What would you recommend to use in such a situation (transparent actors with
transparent - as described above - cutting planes) instead of IPW ?

Since I already made a demo tcl script for reproducing the problem here it
I paste it here, since I found that the mailing list doesn't handle emails
with attachments properly.

I modified the IPW demo: \Examples\GUI\Tcl\ImagePlaneWidget.tcl by adding a
transparent sphere actor in the "middle" of the scene.

Thanks a lot,


package require vtk
package require vtkinteraction

# This example demonstrates how to use the vtkImagePlaneWidget 
# to probe a 3D image dataset with three orthogonal planes.  
# Buttons are provided to:
# a) capture the render window display to a tiff file
# b) x,y,z buttons reset the widget to orthonormal 
#    positioning, set the horizontal slider to move the
#    associated widget along its normal, and set the
#    camera to face the widget  
# c) right clicking on x,y,z buttons pops up a menu to set 
#    the associated widget's reslice interpolation mode 

# Start by loading some data.
vtkVolume16Reader v16
  v16 SetDataDimensions 64 64
  v16 SetDataByteOrderToLittleEndian
  v16 SetFilePrefix "$VTK_DATA_ROOT/Data/headsq/quarter"
  v16 SetImageRange 1 93
  v16 SetDataSpacing 3.2 3.2 1.5
  v16 Update

scan [[v16 GetOutput] GetWholeExtent] "%d %d %d %d %d %d" \
        xMin xMax yMin yMax zMin zMax

set spacing [[v16 GetOutput] GetSpacing]
set sx [lindex $spacing 0]
set sy [lindex $spacing 1]
set sz [lindex $spacing 2]

set origin [[v16 GetOutput] GetOrigin]
set ox [lindex $origin 0]
set oy [lindex $origin 1]
set oz [lindex $origin 2]

# An outline is shown for context.
vtkOutlineFilter outline
  outline SetInput [v16 GetOutput]

vtkPolyDataMapper outlineMapper
  outlineMapper SetInput [outline GetOutput]

vtkActor outlineActor
  outlineActor SetMapper outlineMapper

# The shared picker enables us to use 3 planes at one time
# and gets the picking order right
vtkCellPicker picker
  picker SetTolerance 0.005

# The 3 image plane widgets are used to probe the dataset.
vtkImagePlaneWidget planeWidgetX
  planeWidgetX DisplayTextOn
  planeWidgetX SetInput [v16 GetOutput]
  planeWidgetX SetPlaneOrientationToXAxes
  planeWidgetX SetSliceIndex 32
  planeWidgetX SetPicker picker
  planeWidgetX SetKeyPressActivationValue "x"
  set prop1 [planeWidgetX GetPlaneProperty]
  $prop1 SetColor 1 0 0  

vtkImagePlaneWidget planeWidgetY
  planeWidgetY DisplayTextOn
  planeWidgetY SetInput [v16 GetOutput]
  planeWidgetY SetPlaneOrientationToYAxes
  planeWidgetY SetSliceIndex 32
  planeWidgetY SetPicker picker
  planeWidgetY SetKeyPressActivationValue "y"
  set prop2 [planeWidgetY GetPlaneProperty]
  $prop2 SetColor 1 1 0
  planeWidgetY SetLookupTable [planeWidgetX GetLookupTable]

# for the z-slice, turn off texture interpolation:
# interpolation is now nearest neighbour, to demonstrate
# cross-hair cursor snapping to pixel centers
vtkImagePlaneWidget planeWidgetZ
  planeWidgetZ DisplayTextOn
  planeWidgetZ SetInput [v16 GetOutput]
  planeWidgetZ SetPlaneOrientationToZAxes
  planeWidgetZ SetSliceIndex 46
  planeWidgetZ SetPicker picker
  planeWidgetZ SetKeyPressActivationValue "z"
  set prop3 [planeWidgetZ GetPlaneProperty]
  $prop3 SetColor 0 0 1
  planeWidgetZ SetLookupTable [planeWidgetX GetLookupTable]

set current_widget planeWidgetZ
set mode_widget  planeWidgetZ

# Create the RenderWindow and Renderer
vtkRenderer ren1
vtkRenderWindow renWin
  renWin AddRenderer ren1
#### New (by Istvan)
# Add a semi transparent sphere Actor

vtkSphereSource sphere
    sphere SetThetaResolution 8 
    sphere SetPhiResolution 8
    sphere SetRadius 100
vtkPolyDataMapper sphereMapper
    sphereMapper SetInput [sphere GetOutput]

vtkProperty property
  property SetColor 1.0 0.3882 0.2784
  property SetOpacity 0.99
vtkActor sphereActor
    sphereActor SetMapper sphereMapper
    sphereActor SetProperty property
    sphereActor SetPosition 99 99 99
ren1 AddActor sphereActor

# Add the outline actor to the renderer, set the background color and size
ren1 AddActor outlineActor
renWin SetSize 600 600
ren1 SetBackground  0.1 0.1 0.2

# Create the GUI
wm withdraw .
toplevel .top
wm title .top "vtkImagePlaneWidget Example"
wm protocol .top WM_DELETE_WINDOW ::vtk::cb_exit

set popm [menu .top.mm -tearoff 0]
set mode 1
$popm add radiobutton -label "nearest" -variable mode -value 0  \
           -command SetInterpolation
$popm add radiobutton -label "linear" -variable mode -value 1  \
           -command SetInterpolation
$popm add radiobutton -label "cubic" -variable mode -value 2  \
           -command SetInterpolation

set display_frame [frame .top.f1]

set ctrl_buttons [frame .top.btns]

pack $display_frame $ctrl_buttons \
        -side top -anchor n \
        -fill both -expand f

set quit_button [button $ctrl_buttons.btn1  \
        -text "Quit" \
        -command  ::vtk::cb_exit]

set capture_button [button $ctrl_buttons.btn2  \
        -text "Tif" \
        -command CaptureImage]

set x_button [button $ctrl_buttons.btn3  \
        -text "x" \
        -command AlignXaxis]

set y_button [button $ctrl_buttons.btn4  \
        -text "y" \
        -command AlignYaxis]

set z_button [button $ctrl_buttons.btn5  \
        -text "z" \
        -command AlignZaxis]

set last_btn -1
bind $x_button <Button-3> "set last_btn 0; configMenu; $popm post %X %Y"
bind $y_button <Button-3> "set last_btn 1; configMenu; $popm post %X %Y"
bind $z_button <Button-3> "set last_btn 2; configMenu; $popm post %X %Y"

# Share the popup menu among buttons, keeping
# track of associated widget's interpolation mode
proc configMenu { } {
  global last_btn popm mode mode_widget
  if { $last_btn == 0 } {
    set mode_widget planeWidgetX
  } elseif { $last_btn == 1 } {
    set mode_widget planeWidgetY
  } else {
    set mode_widget planeWidgetZ
  set mode [$mode_widget GetResliceInterpolate]    
  $popm entryconfigure $last_btn -variable mode   

pack $quit_button $capture_button $x_button $y_button $z_button \
        -side left \
        -expand t -fill both

# Create the render widget
set renderer_frame [frame $display_frame.rFm]

pack $renderer_frame \
        -padx 3 -pady 3 \
        -side left -anchor n \
        -fill both -expand f

set render_widget [vtkTkRenderWidget $renderer_frame.r \
        -width 600 \
        -height 600 \
        -rw renWin]

pack $render_widget $display_frame  \
        -side top -anchor n \
        -fill both -expand f

# Add a slice scale to browse the current slice stack

set slice_number [$current_widget GetSliceIndex]

scale .top.slice \
        -from $zMin \
        -to $zMax \
        -orient horizontal \
        -command SetSlice \
        -variable slice_number \
        -label "Slice"

pack .top.slice \
        -fill x -expand f

proc SetSlice {slice} {
  global current_widget 
  $current_widget SetSliceIndex $slice
  ren1 ResetCameraClippingRange
  renWin Render

::vtk::bind_tk_render_widget $render_widget
# Set the interactor for the widgets
set iact [[$render_widget GetRenderWindow] GetInteractor]
planeWidgetX SetInteractor $iact
planeWidgetX On
planeWidgetY SetInteractor $iact
planeWidgetY On
planeWidgetZ SetInteractor $iact
planeWidgetZ On

# Create an initial interesting view
set cam1 [ren1 GetActiveCamera]
$cam1 Elevation 110
$cam1 SetViewUp 0 0 -1
$cam1 Azimuth 45
ren1 ResetCameraClippingRange

# Render it
$render_widget Render

# Supporting procedures

# Align the camera so that it faces the desired widget
proc AlignCamera { } {
  global ox oy oz sx sy sz xMax xMin yMax yMin zMax zMin slice_number
  global current_widget
  set cx [expr $ox + (0.5*($xMax - $xMin))*$sx]
  set cy [expr $oy + (0.5*($yMax - $yMin))*$sy]
  set cz [expr $oy + (0.5*($zMax - $zMin))*$sz]
  set vx 0
  set vy 0
  set vz 0
  set nx 0
  set ny 0
  set nz 0
  set iaxis [$current_widget GetPlaneOrientation]
  if { $iaxis == 0 } {
    set vz -1
    set nx [expr $ox + $xMax*$sx]
    set cx [expr $ox + $slice_number*$sx]
  }  elseif  { $iaxis == 1 } {
    set vz -1
    set ny [expr $oy + $yMax*$sy]
    set cy [expr $oy + $slice_number*$sy]
  } else {
    set vy 1
    set nz [expr $oz + $zMax*$sz]
    set cz [expr $oz + $slice_number*$sz]
  set px [expr $cx + $nx*2]
  set py [expr $cy + $ny*2]
  set pz [expr $cz + $nz*3]

  set camera [ ren1 GetActiveCamera ]
  $camera SetViewUp $vx $vy $vz
  $camera SetFocalPoint $cx $cy $cz
  $camera SetPosition $px $py $pz
  $camera OrthogonalizeViewUp
  ren1 ResetCameraClippingRange 
  renWin Render

# Capture the display and place in a tiff
proc CaptureImage { } {
  vtkWindowToImageFilter w2i
  vtkTIFFWriter writer

  w2i SetInput renWin
  w2i Update
  writer SetInput [w2i GetOutput]
  writer SetFileName image.tif
  renWin Render
  writer Write

  writer Delete
  w2i Delete

# Align the widget back into orthonormal position,
# set the slider to reflect the widget's position,
# call AlignCamera to set the camera facing the widget
proc AlignXaxis { } {
  global xMax xMin current_widget slice_number
  set po [ planeWidgetX GetPlaneOrientation ]
  if { $po == 3 } {
    planeWidgetX SetPlaneOrientationToXAxes
    set slice_number [expr ($xMax - $xMin)/2]
    planeWidgetX SetSliceIndex $slice_number
  } else {
    set slice_number [planeWidgetX GetSliceIndex]
  set current_widget planeWidgetX
  .top.slice config -from $xMin -to $xMax 
  .top.slice set $slice_number

proc AlignYaxis { } {
  global yMin yMax current_widget slice_number
  set po [ planeWidgetY GetPlaneOrientation ]
  if { $po == 3 } {
    planeWidgetY SetPlaneOrientationToYAxes
    set slice_number [expr ($yMax - $yMin)/2]
    planeWidgetY SetSliceIndex $slice_number
  } else {
    set slice_number [planeWidgetY GetSliceIndex]
  set current_widget planeWidgetY
  .top.slice config -from $yMin -to $yMax
  .top.slice set $slice_number

proc AlignZaxis { } {
  global zMin zMax current_widget slice_number
  set po [ planeWidgetZ GetPlaneOrientation ]
  if { $po == 3 } {
    planeWidgetZ SetPlaneOrientationToZAxes
    set slice_number [expr ($zMax - $zMin)/2]
    planeWidgetZ SetSliceIndex $slice_number
  } else {
    set slice_number [planeWidgetZ GetSliceIndex]
  set current_widget planeWidgetZ
  .top.slice config -from $zMin -to $zMax 
  .top.slice set $slice_number

# Set the widget's reslice interpolation mode
# to the corresponding popup menu choice
proc SetInterpolation { } {
  global mode_widget mode 
  if { $mode == 0 } {
    $mode_widget TextureInterpolateOff
  } else {
    $mode_widget TextureInterpolateOn
  $mode_widget SetResliceInterpolate $mode
  renWin Render


-----Original Message-----
From: cpbotha at gmail.com [mailto:cpbotha at gmail.com] On Behalf Of Charl P.
Sent: Tuesday, August 08, 2006 7:58 PM
To: Dean Inglis
Cc: vtkusers archive; istvanmatis at gmail.com
Subject: Re: [vtkusers] How to put vtkImagePlaneWidget behind actors ?

Hi Istvan and Dean,

On 8/8/06, Dean Inglis <dean.inglis at camris.ca> wrote:
> I'm not sure how to address the issue you raise, since I never use 
> vtkImagePlaneWidget in this way (overlay transparent actors/widgets 
> etc.)  Can you provide a short tcl script that uses a vtk test data 
> set (like headsq) that illustrates the problem?  I could take a look 
> in more detail then...

This is an old issue, to do with the even older issue of rendering multiple
intersecting transparent objects correctly.

The problem is that the vtkImagePlaneWidget, in its default configuration,
is considered to be possible transparent (and it can easily be made
transparent).  To fix this in cases where you are not going to use a
colourmap that'll result in a transparent IPW, do the


Dean, you added the GetColorMap() method a long time ago at my request, for
just this purpose.  The documentation does mention how to do this already...
search for "transparent" in

See you,

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