[vtkusers] Useless triangulation in unstructured grid rendering

[John Biddiscombe]

I did forget, that you might be able use a vtkMergeFilter to accomplish 
what you want in this case.

JB

> cc'd developers list for comments/reference
>
> When datasets are modified the filters downstream of them must 
> recompute their outputs. In this case the DataSetSurface filter 
> detects that something has changed, but it isn't clever enough to know 
> that only the scalars have been modified. To solve this problem would 
> require quite significant changes in the way pipeline modified time is 
> passed around and examined.
> For filters which change their outputs over time, but do not change 
> their geometry (ie changing scalars), I am going to add something like 
> a DATA_GEOMETRY_TIME_INVARIANT key to the information passed in the 
> pipeline. This will allow a filter downstream like a surface filter to 
> know that only the scalars will change as the input is modified, but 
> it will still require some extra knowledge (for example, if the 
> timestep changes, the scalars will change, but the filename might also 
> have changed and invalidated the geometry...), by default this key 
> would not be copied and only filters which are geometry invariant 
> under time would set it.
>
> In principle, breaking the modified time into two components - 
> geometry and scalars - would be the most direct way of handling the 
> situation, but it will take some time to 1) implement this and 2) add 
> support into the filters which can take advantage of it.
>
> in short, you'll have to live with it for now, but you can simply 
> modify DatasetGeometry filter to not recompute the mesh and just 
> update the scalars by adding some flag like 
> SetKeepPreviousMeshResult(1) and editing the execute method to not do 
> the triangulation unless it really 'needs' to.
>
> JB
>
>> Dear vtkUsers,
>>
>> I have noticed that when in an ugrid point values are are modified with
>> grid->GetPointData()->SetScalars(pointScalars) a triangulation is 
>> done in
>> vtkDataSetSurfaceFilter. Which is, I guess, useless and very time 
>> consuming. I
>> understand that glList of vertex has to be reconstruct to set new 
>> colors but
>> triangulation result should be taken directly from the filter.
>>
>> Does anyone know why this triangulation is done ?
>>
>> Yours,
>>
>> Jacques Charreyron
>>
>>
>> __________________________________________________________
>> \
>>  \          Jacques Charreyron
>>   \          Société Michelin  
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>
>


-- 
John Biddiscombe,                            email:biddisco @ cscs.ch
http://www.cscs.ch/about/BJohn.php
CSCS, Swiss National Supercomputing Centre  | Tel:  +41 (91) 610.82.07
Via Cantonale, 6928 Manno, Switzerland      | Fax:  +41 (91) 610.82.82