[vtk-developers] Widget picking interfaces only for mouse

[Will Schroeder]

Hi Andrew-

It sounds like you are on to some fun stuff. I would suggest proceeding by 
creating your own
small class hierarchy of widgets and sending them around (we can provide 
ftp space if you need it).
Once all of us see the implementation we can start perfecting the work and 
eventually put it into VTK.

Will

At 06:01 PM 12/6/2003, Andrew Dolgert wrote:
>Hi-
>
>I've been using VTK and its widgets inside a virtual reality environment
>called a Windows CAVE.  I'm wondering whether anyone has thought of
>generalizing events and picking from 2D mouse positions.  While
>implementing widgets and picking for immersive environments, I've
>noticed that 2D mouse (x,y) points are responsible for some redundant
>code.
>
>I don't mean to suggest sweeping changes.  I've implemented the methods
>below because I had to for an immersive environment, and I see many
>great new widgets are on the way.  I can translate them for my own use,
>too, but I thought I'd share this idea.
>
>Current state:
>When the user moves the mouse, every widget separately converts mouse
>movements to transforms in world space.  When the widget calls the
>picker, the picker transforms the mouse x,y into a ray in world space so
>it can find points near the ray.  All three pickers do this same
>transformation, and it is of something already once transformed.  The
>interface to vtkPicker::Pick(x,y,z,renderer) looks general, but it is
>really, in the implementation, a mouse (x,y) and z=0.  Someone was
>thinking it could be more general.
>
>Suggestion:
>If the interactor supplied a transform describing mouse motion, it would
>support other devices like space mice, pinch gloves, and immersive
>trackers.  In addition, widgets would not need to perform a conversion
>to find the transform.
>
>If the interactor supplied, and the picker accepted, a
>vtkImplicitFunction describing the pick, it would reduce computation.
>That function would, for a mouse pick, accept an (x,y,z) in world space
>and return the distance from a ray starting at the screen, pointing in
>the DOP.  For a pinch glove, that implicit function would measure
>distance from the pinch point.  For an immersive wand, it would measure
>distance from a line segment, the wand.
>
>Besides picks and motion, mouse events are used for determining which
>renderer was poked, but that function is now part of the Interactor, so
>it could be performed efficiently for mice, where you need only the
>(x,y) and correctly for immersive systems and display walls, where you
>need to determine whether the wand's line segment intersects a
>renderer's view frustum.
>
>The current picking interface could stand, in case user's use it in
>callbacks.  It would just create the implicit function and pass the job
>on to the more general picker.
>
>- Drew Dolgert, Cornell Theory Center
>
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