[osg-users] Why is setTexCoordArray(0, texcoords) needed if array is modified in-place

[Sebastian Messerschmidt]

Hi Florian

Calling dirty on the modified array should be enough. Are you sure you 
set the useDisplayList to false and the useVertexBufferObject to true?
You don't need to call setTexCoordArray unless you want to assign a 
different array.
I don't quite recall if you need to set the datavariance of the geometry 
to dynamic however, so it might be worth a shot.

Cheers
Sebastian

> Greetings fellow OSG users :)
>
> There is a detail in my code that I found disturbing:
>
>
> Code:
>
> void applyTextureToCenter( MyNameSpace::SpecificNode* floor )
> {
>    MyNameSpace::MyGeode* center = floor->getCenterGeode() ;
>    osg::StateSet* stateSet = center->getOrCreateStateSet() ;
>    MyNameSpace::MyGeometry* geometry = center -> getGeometry() ;
>    const osg::DrawElementsUShort* indices = geometry -> getIndexArray() ;
>    const osg::Vec3Array* vtxArray = static_cast<osg::Vec3Array*>( geometry->getVertexArray() ) ;
>    osg::Vec2Array* texArray = floor ->getTexCoordArray() ;
>    const unsigned numVertex = geometry->getVertexArray()->getNumElements() ;
>    const unsigned numIndices = geometry->getIndexArray() ->getNumIndices() ;
>
>    for ( unsigned id = 0 ; id < numIndices ; ++id )
>    {
>      const unsigned idx = (*indices)[id] ;
>      osg::Vec2 uv ;
>
>      /* *snip*
>       * some texture coordinates computation
>       */
>    
>      (*texArray)[idx].set( uv.x(), uv.y() ) ;
>    }
>
>    geometry->setTexCoordArray( 0, texArray ) ; //Why is this needed ?
>
>      /* *snip*
>       * Code setting the stateSet parameters (shader program, uniforms...)
>       */
>    return ;
> }
>
>
>
>
> I don't understand why the line
> Code:
> geometry->setTexCoordArray( 0, texArray ) ;
>
>   is needed. AFAIK since texArray points to the value given by getTexCoordArray(), we are not actually changing anything...  :?
> I was thinking that maybe it was because setTexCoordArray() caused dirty() to be called, causing re-evaluation of the texture coordinates, but calling
>
> Code:
> geometry->getTexCoordArray(0)->dirty() ;
>
>
> is not enough for my texture to be displayed.
>
> So I went on and looked at the code for setTexCoordArray:
>
> Code:
> openscenegraph/OpenSceneGraph/blob/master/src/osg/Geometry.cpp
>
>
> I see that it is calling
> Code:
> geometry->dirtyDisplayList() ;
>
>   but since we are using VBOs (Vertex Buffer Objects) and not display lists that should not do anything.
> The code is also calling
> Code:
> geometry->addVertexBufferObjectIfRequired()
>
> , which should itself call
>
> Code:
> texArray->setVertexBufferObject(geometry->getOrCreateVertexBufferObject());
>
>
> , which AFAIK should not be changing anything here either, since it is setting the array to use the existing VBOs (which should already be the case).
>
> What is your take on this? There must be something I'm missing.
>
> Thank you!
>
> Best regards,
> Florian.
>
> ------------------
> Read this topic online here:
> http://forum.openscenegraph.org/viewtopic.php?p=68035#68035
>
>
>
>
>
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