[vtkusers] Toggling ScalarVisibility ruins actor's backface color

[joopeter]

Hi everyone

   assume that you have a scene with one actor having different front and
backface color.
   *Frontface *color: *RED  *RGB(1,0,0)
   *Backface *color:  *BLUE *RGB(0,0,1)
   During the 1st rendering of course they will look like as specified.
Check the attached first two images.
   (step1-frontface-red-OK.png, step2-backface-blue-OK.png)

   When I turn *on* vtkPolyDataMapper's ScalarVisibility the rainbow scalars
are also looks fine. Check the attached third image,
step3-scalar-mapping-OK.png
 
   However when i turn *off* the ScalarVisibility again (like it was the
case for the initial step) *the previously defined blue actor backface color
become red*, step4-backface-become-red-NOTOK.png

   What is *even more strange* is that from that point *changing the actor's
backface color is not possible*!
   Also any change on the *frontface color applies now as backface color as
well* :(

   I faced this issue in our C++ project first. For this forum topic I built
a TCL demo of my own to reproducate the problem.
   (That TCL is based on the well-known VTK example located at
\Examples\Rendering\Tcl\rainbow.tcl)

   How to reproducate:
   During rendering you can issue user commands by pressing 'u' key. On that
window you can do

     - set the scalar visibility to on or off by entering the following tcl
commands
            planeMapper ScalarVisibilityOff
            planeMapper ScalarVisibilityOn

     - change the front or backface color
           eval [planeActor GetProperty] SetColor 1.0 0.0 0.0
           backProp SetColor 0.0 0.0 1.0

   *Can you spot why it happened?*

   The problems comes by using VTK 5.8.0 on WinXP 32bit and on different 64
bit Linux machine too.

regards,
Peter

My attachments:
http://vtk.1045678.n5.nabble.com/file/n5714065/step1-frontface-red-OK.png
step1-frontface-red-OK.png 
http://vtk.1045678.n5.nabble.com/file/n5714065/step2-backface-blue-OK.png
step2-backface-blue-OK.png 
http://vtk.1045678.n5.nabble.com/file/n5714065/step3-scalar-mapping-OK.png
step3-scalar-mapping-OK.png 
http://vtk.1045678.n5.nabble.com/file/n5714065/step4-backface-become-red-NOTOK.png
step4-backface-become-red-NOTOK.png 
http://vtk.1045678.n5.nabble.com/file/n5714065/actorBackfaceColorProblem.tcl
actorBackfaceColorProblem.tcl 

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