[vtk-developers] vtkPicker, vtkCellPicker, vtkPointPicker and vtkCompositePolyDataMapper

[David Gobbi]

Well, I don't use composite data in any of my own software and I'm not
familiar with the use cases, so I don't have the answer.  Hopefully someone
else can chime in.

Regards,
 - David


On Tue, Dec 13, 2016 at 1:39 PM, Andreas Buykx <A.Buykx at dianafea.com> wrote:

> What would be a good way to extend the pickers for picking composite data?
> Is it sufficient for all use cases of composite data set picking to store
> the vtkDataObject and flat index of a picked composite data set, and set
> the vtkDataSet to zero? That ought to be pretty easy to implement and it
> would be sufficient I think for our use. Are there other approaches that
> should be considered?
>
> Any thoughts?
>
> Kind regards,
> Andreas
>
>
> ------------------------------
> *From:* David Gobbi [david.gobbi at gmail.com]
> *Sent:* Tuesday, December 13, 2016 12:58 AM
> *To:* Andreas Buykx
> *Cc:* vtk-developers at vtk.org
> *Subject:* Re: [vtk-developers] vtkPicker, vtkCellPicker, vtkPointPicker
> and vtkCompositePolyDataMapper
>
> Hi Andreas,
>
> I think that a remedial fix would be to add a check in vtkPointPicker::IntersectWithLine()
> so that it returns VTK_DOUBLE_MAX if "input" is NULL.  Likewise, the
> vtkCellPicker::IntersectXXWithLine() methods can return VTK_DOUBLE_MAX if
> the mapper input is NULL.  This won't make multi-block data pickable, but
> at least it stop the pickers from crashing the program.
>
> Then, after that remedial fix is done, the picker could be modified to
> detect and pick multi-block data.
>
>  - David
>
>
> On Mon, Dec 12, 2016 at 4:50 AM, Andreas Buykx <A.Buykx at dianafea.com>
> wrote:
>
>> Hi all,
>>
>>
>>
>> I have pipelines that process vtkMultiBlockDataSet and I want to map
>> those using vtkCompositePolyDataMapper. This works fine, except that
>> picking the rendered composite data set causes a crash. This is because
>> vtkPicker, vtkCellPicker and vtkPointPicker assume that vtkMapper always
>> maps a vtkDataSet which is not true in this case. Specifically
>> vtkCellPicker::IntersectActorWithLine and vtkPointPicker::IntersectWithLine
>> will crash, and since vtkPicker::DataSet may get set to 0, any callers fo
>> vtkPicker::GetDataSet that expect a non-null data set will run into
>> problems as well. AFAIK there is no picker implementation that works well
>> with composite data sets, is there?
>>
>>
>>
>> This issue is a blocker for me to integrate vtkCompositePolyDataMapper,
>> so I am going to fix this either by patching our own VTK build or
>> contributing a change to VTK. To do this the right way (I prefer to
>> contribute), I would like some advice/steer on how to fix this issue.
>>
>>
>>
>> A minimally invasive approach would be to add members to vtkPicker to
>> store a vtkDataObject and a flat index of the picked dataset, and set those
>> in case the mapper contains a composite dataset. The IntersectWithLine
>> methods would have to be refactored to allow iterating over the blocks of a
>> vtkDataObject.
>>
>>
>>
>> Kind regards,
>>
>> Andreas
>>
>>
>>
>>
>>
>>
>>
>> *DIANA FEA BV *
>>
>> *Software Developers and Analysis Consultants for Civil and Geotechnical
>> Engineering *
>>
>>
>>
>> Delftechpark 19a, 2628XJ, Delft, The Netherlands
>>
>> Tel: +31 88 34262 15 (Direct) │ Tel: +31 88 34262 00 (Switchboard) │ Fax:
>> +31 88 34262 99
>>
>> http://dianafea.com
>>
>>
>>
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