[osg-users] transparency becomes dark

Gordon Tomlinson gordon.tomlinson at sensor.com
Wed Jul 30 05:35:55 PDT 2008


OGL sets up a default material , you may be picking this up

-----Original Message-----
From: osg-users-bounces at lists.openscenegraph.org
[mailto:osg-users-bounces at lists.openscenegraph.org] On Behalf Of Dieter
Pfeffer
Sent: Wednesday, July 30, 2008 8:09 AM
To: OpenSceneGraph Users
Subject: Re: [osg-users] transparency becomes dark



Thanks Ulrich and Dimi


I supposed that it has s.th to do with the missing material paramters; my
idea was to change the original material of the node, therefore I set:

osg::StateSet *ss = loadedModel ->getOrCreateStateSet();
osg::Material* blendMaterial =
(osg::Material*)(ss->getAttribute(osg::StateAttribute::MATERIAL));

but the material is always NULL so I don't have the original material


Is this the wrong function call ?


Dieter



Unclassified Mail

-----Original Message-----
From: osg-users-bounces at lists.openscenegraph.org
[mailto:osg-users-bounces at lists.openscenegraph.org]On Behalf Of Ulrich
Hertlein
Sent: Saturday, 26 July, 2008 08:08
To: OpenSceneGraph Users
Subject: Re: [osg-users] transparency becomes dark


Hi Dieter,

Dieter Pfeffer wrote:
> I am trying to set the object transparency from 1.0 -> 0.0 and vice 
> versa; but when I start changing the alpha of the material the object 
> becomes dark.
>
> I have changed the material parameters but without success; when I 
> look in the loaded model (for example cow.osg) for material, the 
> material is always null.
>
> I have modified the osgviewer example and attached it.
>
> Could s.o. give me a hint what I am doing wrong ?

You're creating a new Material that overrides the material of the node
you're fading.  However, you're not setting the Material properties
(ambient, diffuse, specular, emissive, shininess) and the default values for
Material are unlikely to match that of the node you're trying to blend.
Hence when you override the original material it will switch from the
original settings to the default Material.

For an experiment, have a look at any .osg file and look at the material
properties.  Then set those values on the 'blendMaterial' node you're
creating and it should look smooth.

You're probably better off modifying the original Material(s) of the node
hierarchy.  Or try another approach, like using blendcolor.

Cheers,
/ulrich

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