Fixed text size query...

• To: "'visad-list@xxxxxxxxxxxxx'" <visad-list@xxxxxxxxxxxxx>
• Subject: Fixed text size query...
• From: Jim K <jimk@xxxxxxxxxx>
• Date: Wed, 12 Sep 2001 08:44:03 +1000

Hello,

I have written a renderer and some shadow types to keep visad
objects locked on the screen, ie. their position and size does
not vary as the display is zoomed and/or panned.

I am working on an application that displays town names over
a map of Australia, and only need to keep the size of the
text constant.

I have tried, but have been unable to change the code in my
shadow type to allow the font size to remain constant, but the
position of the text to move.

I will explain my existing "screen locking" code and show
you what I mean. :)

I have extended a shadow type class, and have overriden the
addTextToGroup method.  This allows me to add my own
transform group and perform scale and translation matrix
operations.

My transform group undoes the scaling and translation that
the parent transform group does, thus keeping the text
locked to the screen.  This is all done within the controlChanged
method of the shadow type, which is triggered when the
projection control matrix is changed.

I have made some minor changes to make the code
more readable...


public void
controlChanged(
  ControlEvent theEvent_IN
  )
{

  double [] aTranslation = new double[ 3 ];
  double [] aScale = new double[ 1 ];


  // Get the projection matrix from the event and extract the
  // translation into the aTranslation array, and the scale into
  // the aScale array.

  getTranslationAndScale_( theEvent_IN, aTranslation, aScale );


  // Move the text back to its original location.

  Vector3d theTranslationVector = new Vector3d();

  theTranslationVector.x = -1 * aTranslation[ 0 ] / aScale[ 0 ];
  theTranslationVector.y = -1 * aTranslation[ 1 ] / aScale[ 0 ];
  theTranslationVector.z = -1 * aTranslation[ 2 ] / aScale[ 0 ];


  // Re-scale and set the translation.

  Transform3D theTransform = new Transform3D();
  theTransform.set( 1 / aScale[ 0 ], theTranslationVector );


  // theTransformGroup_ is a member variable which has
  // been added as a child to the transform group that was
  // passed into the addTextToGroup method.

  theTransformGroup_.setTransform( theTransform );

} // MyShadowTupleTypeJ3D.controlChanged()



Ok, so there is my current screen-locking code.  I have
tried to do the following:

  Transform3D theTransform = new Transform3D();
  theTransform.set( 1 / aScale[ 0 ] );

this keeps the text size constant, but the text does not
move as I want it to when I zoom in or out.  The scaling
affects the translation and this is where I get stuck.
I have tried to "undo" the effects of the scaling on the
translation but have had no luck.

Can someone help out?  Any help would be greatly
appreciated.

Thanks,
Jim.
---
Jim Koutsovasilis
Bureau of Meteorology, Australia
jimk@xxxxxxxxxx

• Follow-Ups:
  • Re: Fixed text size query...
    • From: Bill Hibbard
  • Re: Fixed text size query...
    • From: From: Bill Hibbard <hibbard@xxxxxxxxxxxxxxxxx>