Re: My own billboard?

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Angus Dorbie (dorbie++at++multipass.engr.sgi.com)
Thu, 15 Jan 1998 18:39:13 -0800

On Jan 14, 1:50pm, Mario Veraart wrote:
> Subject: Re: My own billboard?
> >
> > Hey folks,
> >
> > I need to implement my own "Billboard" so that I may articulate the
> > geometry that I am "Billboarding".
> >
> > This geometry will be attached below a couple pfDCS's so it's coordinate
> > system will be a bit different than the world coordinate system.
> >
> > O (pfScene)
> > / \
> > / \
> > / O-----(pfDCS:myBillboard)
> > / (pfDCS)
> > /
> > (eye)
> >
> > My problem is how do I come up with the angles in myBillboard
coordinates
> > that will make it face my eye?
> >
> > Any examples would be great.
>
> You dont need to know this. Performer will calculate the angle needed
> for an axis billboard or a point billboard. You just model that the
> geometry of the billboard is visible looking from a point on the
> positive y-axis towards the origin.
>
But this only applies to pfBillboards which are derived from pfGeodes
so a different scene graph approach is required. It's also desirable,
pfDCSs are not the prefferred method for billboarding ;-)

ps you need atan2f using eye position - billboard center in x & y to
get heading. Then you use the sin and cos of this heading you multiply
x & y (respectively) for x and y -x (respectively) for y for each
vertex (I've probably gotten the signage wrong).

This is all highschool trig and you should really buy a book on simple
trigonometry or a computer graphics text to help with this stuff.

Cheers,Angus.

-- 
  "The Revolution 3D can be thought of as a chariot being pulled by three
powerful horses, each representing 3-D, 2-D and MPEG acceleration. While
many competing technologies may offer three horse chariots, often only
one of the three horses is fast" - industry analyst Richard Doherty,
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