[vtk-developers] Cleanup of crufty code in vtkPicker

[David Gobbi]

Hi Will,

I can understand that, but right now going through the pick list is
really the only valid way of doing that anyway, because a PickEvent is
not generated for every prop that goes into the pick list.  Please
bear with me while I explain what the current code for vtkPicker (and
vtkAreaPicker) does:

For each "hit" prop, that prop is added to the pick list.  If and only
if that prop is closer to the camera than any previously hit prop,
prop->Pick() is called and a PickEvent is generated.

So, in my opinion, it's better for only one PickEvent to be generated
(for the closest prop), rather than to have PickEvent generated for
just "some" of the props that go into the pick list.

The other solution, ensuring that a PickEvent is generated for every
prop that goes into the PickList, would require a fairly radical
redesign of vtkPicker and its subclasses because this->CellId,
this->Mapper, etc. are all stored only if the current prop is the
closest to the camera.   That is why PickEvent is currently only
generated if the current prop is the closest to the camera.

   David


On Tue, Jan 5, 2010 at 9:26 AM, Will Schroeder
<will.schroeder at kitware.com> wrote:
> David-
>
> I believe that the idea behind invoking the PickEvent multiple times was so
> that if you could perform multiple "operations" on each prop picked, for
> example placing a bounding box, or changing the color of each picked prop,
> etc. I realize that there is an alternative way by processing the pick list
> after the end pick event is emitted. I guess I don't understand why you want
> to change behavior, is there a compelling reason? Performance? I agree the
> risk is small, but I'd rather not aggravate anybody if we can help it.
>
> Will
>
> On Mon, Jan 4, 2010 at 3:13 PM, David Gobbi <david.gobbi at gmail.com> wrote:
>>
>> Hi All,
>>
>> I'd like to do a little clean-up of vtkPicker so that the code and the
>> header documentation are in better agreement with each other.  There
>> is a chance that there could be some backwards compatibility problems,
>> but I think that the risk is very small.  The interface of the class
>> will not be changed.
>>
>> So, here is the main adjustment:
>>
>> Right now, the picker might invoke PickEvent for more than one prop
>> during the pick, and I don't think that this is correct behavior.  I
>> want to change the code so that the PickEvent is only invoked for the
>> front-most prop under the cursor.  Any objections?  This change will
>> not require modification to PointPicker or CellPicker, and should not
>> require modification to any third-party subclasses, either.
>>
>>   David
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>
>
> --
> William J. Schroeder, PhD
> Kitware, Inc.
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