[osg-users] osgText - shimmer...wavy

Jason Beverage jasonbeverage at gmail.com
Tue Oct 16 06:38:10 PDT 2007


Hi Sherman and Robert,

I'm running into precision issues with osgText as well, mostly with
intersections.  I'm positioning my text using a MatrixTransform and still
see the shimmering that Sherman is talking about, although its not too
terrible in my situation since my text objects aren't extremely far away
from the origin as in Sherman's case.

The issue I'm having is that I'm using character size mode SCREEN_COORDS.
When I zoom in close to the text, it is visible, but intersection tests fail
because of the float precision used internally for osgText (as far as I can
tell).

Having osgText use double internally could potentially solve this issue, but
I think if it were to still use PrimitiveFunctor to perform intersection
that PrimitiveFunctor would need updated to support double values as well.

Thanks,

Jason

On 10/16/07, sherman wilcox <wilcox.sherman at gmail.com> wrote:
>
> See attached.
>
> On 10/16/07, Robert Osfield <robert.osfield at gmail.com> wrote:
> > Hi Sherman,
> >
> > This sounds like a precision issue related to the computation of the
> > text scaling - which is done in floats.
> >
> > Could you modify the osgfadetext example to have text they way you are
> > setting it up and see if it reproduce the problem, or perhaps send a
> > small .osg file that reproduces the issue and then I can have a look
> > at it.  It might be that we need to have a code path in osgText for
> > using double maths internally.
> >
> > Robert.
> >
> > On 10/16/07, sherman wilcox <wilcox.sherman at gmail.com> wrote:
> > > I'm using osgText with the character size mode of
> > > OBJECT_COORDS_WITH_MAXIMUM_SCREEN_SIZE_CAPPED_BY_FONT_HEIGHT. The text
> > > is position on an ellipsoid model with ECEF coordinates. When the text
> > > is smaller than the maximum font height I notice that the text is
> > > somewhat wavy when I zoom in and out. Sort of shimmers. Once the text
> > > has realized it's maximum size the effect is much less noticable,
> > > sometimes completely gone. Could this be a floating point precision
> > > issue down in the bowels of osgText? BTW, I'm using an
> > > osg::MatrixTransform node to position the text.
> > >
> > > Any ideas?
> > > _______________________________________________
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> > >
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