> From: Adam Belmont <[EMAIL PROTECTED]>
>
> I am trying to pick points (which may be as small as a pixel) and lines
> in a Canvas3D.
> I 'm using PickObject.java from the utilities package. Problem is that
> it is very difficult to pick the exact spot on the screen with the
> mouse. So I'd like to be able to give a bit of variable tolerance the
> picking mechanism.
> I see that PickObject generates a PickRay and then attempts to intersect
> it with objects found underneath the picking location. I think a
> solution for this problem would be to vary the diameter of the PickRay,
> in effect creating a PickCylinder instead.
I'll be replying to this in several parts. I've got new picking utilities and a
example which shows how they are used, but the mailing list software won't allow
me to post a message larger than 40K.
This message will tell you about the pieces to come. The following messages
will have:
PickingExt.jar -- source for a replacement for the picking utilities
PickingExtDoc.jar -- documentation for the new utilities
PickingExtTest.jar -- files to add to the PickTest example directory
to show how the new picking works.
Here are the details:
Picking lines and points requires a PickShape which can intersect with the
primtives. J3D 1.1 supports picking using a Bounds object for the pick shape
and a BoundingPolytope can be used to make a volume represents the area around
the mouse position. The problems is that the picking utilities in J3D 1.1 only
understand how to generate PickRay's, not PickBounds.
The pickingExt package extends the com.sun.j3d.utils.behaviors.picking package
to support line/point picking using a pick "aperture". The aperture is a closed
loop of points around 0,0 in window coordinates (see PickObject.java). When
using an aperture, the utility will generate a bounding polytope which extends
from the eye through the edges of the pick aperature.
The default aperture is a 4 pixel square around the mouse point. The result is
similar to using a pick cylinder as other emails have suggested.
A couple notes:
1) We are distributing the updated version of the picking utilities as source
since we can't update the "official" utilties until J3D 1.2. If you like, you
can change the package for the utilities to
com.sun.j3d.utils.behaviors.pickingExt, but you are responsible for building and
maintaining the extended utilities. I'll be posting updated versions of these
utilities to the interest alias if bug fixes or extensions are needed.
2) Both the SHAPE_RAY and SHAPE_APERTURE modes work correctly under parallel and
perspective views.
3) J3D 1.1.1 has a couple bugs which show up when using these utilties. First,
only the endpoints of lines can be picked for SHAPE_APERTURE picking. Second,
the "bounds" picking test will fail for SHAPE_APERTURE picking, so use
SHAPE_RAY_APERTURE for best results. Both these bugs will be fixed in the
upcoming 1.1.2 release.
4) For doing pick aperture picking, the best performance comes from using
SHAPE_RAY_APERTURE mode. This uses a pick ray for the "bounds" phase of picking
and then a pick aperture for the "geometry" phase of picking.
Hope this helps. Let me know if you have problems,
Doug Gehringer
Sun Microsystems
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