[vtk-developers] vtkLookupTable::Build() behaviour ?
sbarre at claranet.fr
Wed Jul 19 06:20:48 EDT 2000
I was wondering if the vtkLookupTable::Build() behaviour is accurate, or
It seems that if one wants to *rebuild* a table that has been built and
modified using SetTableValue(), then one has to issue this strange series
of commands to get it rebuilt correctly :
Here is why :
Suppose that my app creates a LUT called lut with opacity = 'x'. The only
thing I know is its name, and its nb of colors. I do not know about 'x'
(although I might, of course, GetxxxRange(), but I do not want). From time
to time I'd like to manually insert values in that table to change the
opacity of a specific range of entries to 0.0. Therefore, I'd like the
table to rebuild itself to set the old 0.0 range back to 'x' (I do not know
about the properties of the LUT, then I must use ::Build()) , than set the
new range to 0.0 :
step 0) : create the lut (vtkLookupTable), and set it (SetxxxRange and so on)
then from time to time :
step a) : rebuild the lut (lut Build) to set alpha to 'x'
step b) : insert 0.0 alpha values (SetTableValue) in a specific range
But step a) will fail ! Thus, I'll get a LUT where the old range and the
new range are merged, and at the end my LUT will probably be full of 0.0
step a) fail because of the implementation. As it has not changed since
3.1, I'm quite sure it has been done on purposes, but I do not understand why :
if ( this->Table->GetNumberOfTuples() < 1 ||
(this->GetMTime() > this->BuildTime && this->InsertTime < this->BuildTime) )
[...] code that perform the build
Notice the test : (this->GetMTime() > this->BuildTime && this->InsertTime
< this->BuildTime) )
This means that in order to allow the build, the LUT must have been
modified since the last build (which seems logical), AND the last insertion
must have been done before the last build (<=> the last build has been done
after the last insertion).
The last condition is strange. In fact, it states that once insertion has
been done (which has been done after an initial build, otherwise it's
stupid), it is no more possible to rebuild the LUT ! Very strict...
But this can be circumvented because the last line :
is run even if the build is not done ! (it's out of the test).
- I have performed an initial build, then an insertion :
GetMTime > BuildTime && InsertTime > BuildTime
- I try a this->Build() :
this *fails* (because of the previous condition) BUT now :
GetMTime < BuildTime && InsertTime < BuildTime
- This leaves us the first condition to fix, so let's : this->Modified()
GetMTime > BuildTime && InsertTime < BuildTime
which is the required condition to Build()
- this->Build() : will work
Strange, huh ?
I do not know if it's a feature. If it's a bug (the last line should be in
the test), then I'd be curious to know how I might rebuild a table and
perform new insertion without destroying/recreating an object...
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