[Paraview] custom filter doesn't update property in the Paraview UI

[Utkarsh Ayachit]

> I'll check the meaning of MTime.

See the implementation of vtkSetMacro() in vtkSetGet.h. Every time the
value changes, it call this->Modified() which updates the MTime. Since
VTK is a demand-driven pipeline, changes to MTime is what tells the
pipeline that the algorithm has been modified and needs reexecution.
If one modifies the MTime in RequestData() (the method called by the
pipeline to process the input to produce output), the pipeline thinks
the filter is always dirty and that can cause unexpected side effects.


> I'd need something similar to an image resize filter. The output size should
> be identical to the input size, when the filter is first attached to the
> input. The output size should be shown in the UI and the user should be able
> to enter a different output size.

This is possible. Let me see if I can find you a simple example for
the same. I'll get back to you.