Re: [osg-users] Flipping the normals

[Mike Wittman]

Hi Mike,

 

Take a look at OpenGL's two-sided lighting support via
glLightModel/GL_LIGHT_MODEL_TWO_SIDE (and exposed in OSG with
osg::LightModel).  I think that's the more elegant solution your looking
for.

 

 

Mike Wittman

[EMAIL PROTECTED]  

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From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Michele
Bosi
Sent: Tuesday, August 28, 2007 4:45 PM
To: osg-users@lists.openscenegraph.org
Subject: [osg-users] Flipping the normals

 

Hello,
I've a relatively easy task to accomplish, that is to render a mesh both
from inside and outside. 
To do this i put the mesh under two different Geodes, in one i set the
front face to "clock wise" on the other I set the front face to "counter
clock wise" turning on the backface culling (or putting the object into
a single Geode turning off the backface culling). The problem is that in
one case (when I render the "interior" of the mesh) the polygons are not
lit since the normals are (of course) not flipped, that is they remain
oriented "outward". 
My question is: how can I flip the normals? should I create two distinct
meshes, one with the original normals and the other with inverted
normals (modifying manually the normal buffers, and doubling the memory
usage) or there is a more elegant way to do that, for example a
node/state like GL_PLEASE_FLIP_MY_NORMALS that can take care of this
task automatically? 
Cheers,
Mike

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Re: [osg-users] Flipping the normals

[Gerrick Bivins]

Sounds like you want something like:

osg::ref_ptr lightModel = new osg::LightModel;
lightModel->setTwoSided(true);
myTwoSidedGeode->getOrCreateStateSet()->setAttribuiteAndModes(lightModel.get
()*);*
**
Might not be the exact syntax but pretty close.


On 8/28/07, Michele Bosi <[EMAIL PROTECTED]> wrote:
>
> Hello,
> I've a relatively easy task to accomplish, that is to render a mesh both
> from inside and outside.
> To do this i put the mesh under two different Geodes, in one i set the
> front face to "clock wise" on the other I set the front face to "counter
> clock wise" turning on the backface culling (or putting the object into a
> single Geode turning off the backface culling). The problem is that in one
> case (when I render the "interior" of the mesh) the polygons are not lit
> since the normals are (of course) not flipped, that is they remain oriented
> "outward".
> My question is: how can I flip the normals? should I create two distinct
> meshes, one with the original normals and the other with inverted normals
> (modifying manually the normal buffers, and doubling the memory usage) or
> there is a more elegant way to do that, for example a node/state like
> GL_PLEASE_FLIP_MY_NORMALS that can take care of this task automatically?
> Cheers,
> Mike
>
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>
>
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Re: [osg-users] Flipping the normals

[Michele Bosi]

Thanks very much guys, osg::LightModel/GL_LIGHT_MODEL_TWO_SIDE seems
exactly what I needed.
Thankyou,
Mike
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Re: [osg-users] Flipping the normals

[Paul Martz]

> Thanks very much guys, 
> osg::LightModel/GL_LIGHT_MODEL_TWO_SIDE seems exactly what I needed.
> Thankyou,
> Mike

In case it's not obvious, with two-sided lighting you do not need to
re-parent your mesh to two Geodes with different face culling. You should be
able to use a single Geode, face culling disabled, and two-sided lighting
enabled.
   -Paul

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Re: [osg-users] Flipping the normals

[Michele Bosi]

Thanks Paul,
just wanted o add that I am very glad that when it comes to render
states OSG remains so close to OpenGL and doesn't abstract too much
from it, as this case proves, this lets users to reuse their prior
knowledge of OpenGL and makes the library really flexible,
long life to OSG! :)
Mike
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