Re: OOps, Re: Fixed text size query...

• To: jimk@xxxxxxxxxx, visad-list@xxxxxxxxxxxxx
• Subject: Re: OOps, Re: Fixed text size query...
• From: Tom Rink <rink@xxxxxxxxxxxxx>
• Date: Fri, 14 Sep 2001 08:51:45 -0500

Hi Jim,

I've solved a similiar problem to yours, except for contour value
labels.  Here's my controlChanged() method with a few comments:

            .
            .
            .

   public void controlChanged(ControlEvent e)
   {
     matrix = proj.getMatrix();

     MouseBehaviorJ3D.unmake_matrix(rot_a, scale_a, trans_a, matrix);

     double factor = first_scale/scale_a[0];
     float f_scale = (float) ((scale_a[0] - first_scale)/scale_a[0]);
     trans.getTransform(t3d);

     Vector3f trans_vec
       new Vector3f(f_scale*vertex[3*closest_vert+0],
                    f_scale*vertex[3*closest_vert+1],
                    f_scale*vertex[3*closest_vert+2]);


     t3d.set((float)factor, trans_vec);
     trans.setTransform(t3d);
   }

 -----

I use a little matrix algebra, and a little experimentation, to 
compute the f_scale value, essentially I solve for translation
components required to place the label where I want it, at the 
desired scale.  It works very well, and under all combinations
of transformation although I can only prove it works for pure
scaling, and scaling with translation.  The closest_vert is sort
of the anchor point for the label.

Hope this helps,

TomR
        

Bill Hibbard wrote:
> 
> I wrote:
> 
> > 2. Since you know that:
> >
> >   Transform3D theTransform = new Transform3D();
> >   theTransform.set( 1 / aScale[ 0 ], theTranslationVector );
> >   theTransformGroup_.setTransform( theTransform );
> >
> > works for fixing the location and size, you might try:
> >
> >   Transform3D theTransform = new Transform3D();
> >   theTransform.set( 1 / aScale[ 0 ], theTranslationVector );
> >   Transform3D scale = new Transform3D();
> >   scale.set( 1 / aScale[ 0 ] );
> >   theTransform.mul(scale);
> >   theTransformGroup_.setTransform( theTransform );
> 
> Clearly this should not re-apply the scale, but apply the
> inverse of the translation in 'scale'. That is:
> 
>   Transform3D theTransform = new Transform3D();
>   theTransform.set( 1 / aScale[ 0 ], theTranslationVector );
>   Transform3D translate = new Transform3D();
>   Vector3d inverse = new Vector3d();
>   inverse.x = -theTranslationVector.x;
>   inverse.y = -theTranslationVector.y;
>   inverse.z = -theTranslationVector.z;
>   translate.set( inverse );
>   theTransform.mul(translate);
>   theTransformGroup_.setTransform( theTransform );
> 
> > I may have some detail wrong, like the order of multiplying
> > matrices, but with a few experiments you may get it. When I
> > write such transform matrix code, I always have to experiment
> > to get it right.
> 
> And of course, you can probably accomplish the same thing
> with your original code and experimenting with arithmetic
> operations on the x, y and z values in theTranslationVector.
> 
> Good luck,
> Bill
> ----------------------------------------------------------
> Bill Hibbard, SSEC, 1225 W. Dayton St., Madison, WI  53706
> hibbard@xxxxxxxxxxxxxxxxx  608-263-4427  fax: 608-263-6738
> http://www.ssec.wisc.edu/~billh/vis.html

• References:
  • Fixed text size query...
    • From: Jim K
  • Re: Fixed text size query...
    • From: Bill Hibbard
  • OOps, Re: Fixed text size query...
    • From: Bill Hibbard