[vtkusers] vtkPicker returned actor

[David Gobbi]

The vtkPropPicker is a hardware picker.  When you pick with it, the GPU
renders the scene into a hidden buffer, where each Prop in the scene is
rendered as a different color and with no shading.  So the pick simply
reads this "pick" buffer to see what Prop is under the cursor, and then it
reads the depth buffer to get the depth coordinate.

The vtkCellPicker is a software picker.  It goes through the list of props
that are attached to the renderer, and inspects the data for each prop.  It
essentially shoots a view ray from the camera position, and checks to see
what props are intersected by that ray.

I like the vtkCellPicker because it returns a very precise depth coordinate
(it can do so because it doesn't rely on the depth buffer).  Some people
like the vtkPropPicker because it gives pixel-perfect accuracy, since the
picking exactly matches the rendering.  Some people also insist that the
vtkPropPicker is faster, but that depends on what is in the scene.

 - David

On Tue, Feb 23, 2016 at 4:27 PM, Lonni Besançon <lonni.besancon at gmail.com>
wrote:

> I tried the the CellPicker and it apparently works (pretty late here
> already
> so I did not fully test it, but I have the feeling it's working just fine).
> Would you happen to know why this picker is working while the default one
> was not (or at least not completely)?
>
> Thanks again for the help :)
>
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