[vtkusers] BUG in vtk[Render/ImageWindow]Widget ?
seb-ml-vtk at barre.nom.fr
Sat Sep 2 23:03:52 EDT 2000
I have not seen any serious changes in the CVS regarding the Tk Widgets
(vtkTkRenderWidget, vtkTkImageWindowWidget), nevertheless I guess I found
evidence of a strange and non-compliant behaviour (although I'm still not
sure if it's not a framebuffer problem) :
- widgets are not packed correctly. The Tk documentation is clear about
that : "if a widget is not managed [by pack, grid or any geometry
managers)], it doesn't appear on your display at all". Sadly, this is not
the case with the VTK Tk widgets on two of my computers. Moreover, "[By
unpacking it], the widget gets unmapped so it's not visible". Which does
not work either :) And as the widget visibility gets corrupted, the VTK
widgets accept events where they should not.
- this problem arises only with combination of two different type of
widgets at the same Tk level (which is puzzling),
I'm using Tcl/Tk 8.3.0, the very latest VTK CVS, Windows NT4 SP6, a SGI
Visual 320 and a conventional Home-PC running an 3Dlabs Oxygen GMX 2000.
I noticed the "bug" as I tried to put *both* a render widget and an image
widget in a tabnotebook. You all know what a tabnotebook is :), it's a
convenient GUI metaphor that provides access to "pages" through small
"tabs". Many "Preferences" dialog use this representation, as well as
serious apps as an alternative to the MDI (multidocument interface) scheme.
There is no tabnotebook in the Tcl/Tk distrib. The best tabnotebook is to
be found in the BLT package. There is also one in the Iwidgets package
(Itcl/Itk). I tried BOTH, and was able to reproduce the bug. Then I wrote a
Tk-only script (attached to the email) which basically focus on the problem.
The trick is well-know, given a parent widget...
and two children at the same level...
...you might simulate a tabnotebook by packing a *single* children at a
time. If the user selects another tab, then you unpack the previous
"selection", and pack the new selection.
pack forget old_widget
...will respectively map/unmap the widget relative to its parent, thus
explicitly making it visible or no more visible (but still existing of
The important thing to note is that you cannot pack/unpack a widget A in a
widget P if A is not a children of P. But this is not a problem, because
even if you create a frame and 2 buttons:
there is not display conflict, as nothing is visible until you pack one of
them. Up to you to decide.
Which leads us to the problem. Given a Tk frame and two VTK widgets :
guess what ? even if you did not pack them, the Image Widget is visible
(sort-of). And if you bind the Expose and Configure events to each of them
(as you should)... they will both respond to their respective events !
Simultaneously. And although not packed, not visible, not mapped.
And if you start packing/unpacking one of them in a "tabnotebook" manner,
you will notice that the RenderWidget never shows up. Or sometimes, but
with some parts of the old Image Window widget as a "ghost" background.
Some refresh or framebuffer problem ?
This is demonstrated in the small script attached to this email.
- it creates an imaging and rendering pipeline,
- it creates a vtkRenderWidget and vtkImageWindowWidget at the same level,
- it creates two buttons that will be used to display one widget, or the
=> at this time, there is two buttons on the top (no one has been
selected), and as no widget has been packed, there should not be anything
visible ! But it's not the case, you should already see the content of the
Moreover, I've bound the <Expose> <Configure> to each widget so that they
render themselves automatically and send a message to the standard output,
giving the event/widget names. But if you play with the window, you will
see that both widgets already respond to their events, although they are
not packed, visible or mapped !!
(tests) 8 % winfo viewable $parent.iwid
(tests) 9 % winfo viewable $parent.rwid
(tests) 11 % winfo ismapped $parent.rwid
(tests) 12 % winfo ismapped $parent.iwid
Smashing ? Not finished. If you play with the buttons, you will see that
the pack/unpack trick works for the button, but not for the widget.
Basically, the render widget never shows up.
Still awake ? Be aware that this problem disappears if you use only one
widget, or two widgets of the same type ! Two render widget have no
problem. Two imagewidget neither !
Any clues would be welcome.
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# S?bastien Barr? (Time-stamp: <2000-09-03 04:40:22 barre>
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