[vtkusers] Picking invisible object...vtkPlane ( Simple version ! )

[Sebastien Auclair]

In short, my problem should simply be stated as follows:

The user clicks on the screen an empty area with no actors.
A vtkPlane instance is already existing. (Which of course isn't visible )
I simply need to get the point in space where the plane was
picked\intersected.
While keeping in mind the fact that we are in parallel display mode.





More Details :

The vtkPlane's normal is not always parallel to the display plane's normal.
In which case the returned value (vtkPlane::ProjectPoint) is always correct.
The more perpenticular the vtkPlane's normal is in relation to the Display
plane's normal, the less accurate the intersection coordinates becomes. (It
should be the opposite !)
We are not using any interactor nor interactorStyles...
To know why i need this, just read the first set of mail exchange below.

Thanks !
_______________________________________
Seb

----- Original Message -----
From: "Sebastien Auclair" <sxa at fluent.com>
To: "Charl P. Botha" <c.p.botha at ewi.tudelft.nl>; "VTK Users List"
<vtkusers at vtk.org>
Sent: Monday, July 21, 2003 11:58 AM
Subject: Re: [vtkusers] Picking invisible object !


> This is what we did...
>
> We are not using the interactor features (for different reasons...)
> But we used the code in InteractorStyleTrackball for all the camera and
> object movements...
>
> The following is part of the code for managing the scaling on X axis of an
> hexahedron when draging one of its edge.
>
> +++++++++++++++++++++++++++++
>
> void TKWidget3D::ActorEdgeScale(int x, int y, int oldX, int oldY)
> {
>
> double scale[3];
> float origin[4];
> TKCadObject* obj;
> float ObjCenter [3];
> double yf;
> double scaleFactor, scaleFactor2;
>
> double **rotate;
>
>
>  if (m_currentRenderer == NULL)
>  {
>   return;
>  }
>
>  obj = m_EdgePickedActor;
>  obj->GetOrigin(origin);
>
>
>  rotate = NULL;
>
>
> // Prop3DTransform(obj,ObjCenter, 0, rotate, scale, false);
>
>  float camPos[4];
>  float newPickPt[4];
>  float oldPickPt[4];
>  float pickPos[4];
>  float nrml[4];
>  float pickDisp[4];
>  float t;
>  float IntersPt[4];
>  float oldIntersPt[4];
>
>  int FixedAxis = m_EdgePickedActor->GetEdgeResizeFixedAxis();
>  if ( FixedAxis == 0){ // A transformation that can only take place on the
X
> axis...
>
>   m_currentRenderer->GetActiveCamera()->GetPosition(camPos);
>   m_Picker->GetPickPosition (pickPos);
>
>   origin[0] = pickPos[0];
>   ComputeWorldToDisplay((pickPos[0]), (pickPos[1]), (pickPos[2] ),
> pickDisp);
>   ComputeDisplayToWorld (double(x) , double(y), (pickDisp[2]), newPickPt);
>   ComputeDisplayToWorld (double(oldX), double(oldY),  (pickDisp[2]) ,
> oldPickPt);
>
>   nrml[0] = 1;
>   nrml[1] = 0;
>   nrml[2] = 0;
>
>   vtkPlane::GeneralizedProjectPoint  (newPickPt,pickPos, nrml, IntersPt);
>   vtkPlane::GeneralizedProjectPoint  (oldPickPt,pickPos, nrml,
oldIntersPt);
>
> m_testSphere->SetCenter(IntersPt);
> m_testMapper->Modified();
> m_testMapper->Update();
>
>   scale[0] =  1 ;
>   scale[1] = IntersPt[1] / oldIntersPt[1];
>   scale[2] = IntersPt[2]/ oldIntersPt[2];
>
> ++++++++++++++++++++++++++++++++++++
>
>
> Note the usage of the m_testSphere which is suppose to stay behind the
mouse
> cursor and always move on the vtkPlane.
> It stays on the plane but can't go as far as the mouse cursor...
>
>
> Thanks for any help !
> ____________________________________
> Seb
>
> ----- Original Message -----
> From: "Charl P. Botha" <c.p.botha at ewi.tudelft.nl>
> To: "VTK Users List" <vtkusers at vtk.org>
> Sent: Monday, July 21, 2003 7:08 AM
> Subject: Re: [vtkusers] Picking invisible object !
>
>
> > On Mon, 2003-07-21 at 13:05, Sebastien Auclair wrote:
> > > I need to allow the user to drag a picked object but not in X, Y
> direction
> > > on the display plane.
> > > For instance, he must be able to drag a cube on the World X axis only.
> > > To do that, my approach so far is to create an invisible vtkPlane that
i
> try
> > > to use to compute an intersection point with a ray i create based on
> > > DisplayToWorld and the mouse coordinates.
> >
> > Why don't you just create a new vtkInteractorStyle class?  For instance,
> > you could inherit from the vtkInteractorStyleTrackballActor and simply
> > prevent the PAN mode from being entered, or the Pan() method from being
> > called.
> >
> > This seems far simpler than what you're doing, unless I'm
> > misunderstanding something.
> >
> > --
> > charl p. botha http://cpbotha.net/ http://visualisation.tudelft.nl/
> > _______________________________________________
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>
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