Faulty reflection if front- and backface of a model are drawn in a different way

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What steps will reproduce the problem?

I am using a cell shader implementation, where the outline is created by 
drawing the backfaces in wireframe mode with activated front face culling:
"osg::ref_ptr<osg::StateSet> linestate = node->getOrCreateStateSet();
linestate->setAttribute(new osg::LineWidth(4.0f));
linestate->setAttribute(new osg::CullFace(osg::CullFace::FRONT));
linestate->setAttribute(new osg::PolygonMode(osg::PolygonMode::BACK, 
osg::PolygonMode::LINE));"

The fragment shader draws a black fragment, if the fragment is backface and the 
regular color, if the fragment is front face:
"...
void main()
{
    if (gl_FrontFacing)
    {
        gl_FragColor = lighting();
    }
    else
    {
        gl_FragColor = vec4(0.0, 0.0, 0.0, 0.80);
    }
}
..."

In the reflection image the front- and backface is switched(as seen in the 
picture).
I changed the frontface mode to clockwise for the reflection camera to fix this 
issue.

osgOcean::OceanScene::init(), OceanScene.cpp, line 363

BEFORE:
"// clip everything below water line
            _reflectionCamera=renderToTexturePass( reflectionTexture.get() );
            _reflectionCamera->setClearColor( osg::Vec4( 0.0, 0.0, 0.0, 0.0 ) );
            _reflectionCamera->setCullMask( _reflectionSceneMask );
            _reflectionCamera->setCullCallback( new CameraCullCallback(this) );
            _reflectionCamera->getOrCreateStateSet()->setMode( GL_CLIP_PLANE0+0, osg::StateAttribute::ON );
            _reflectionCamera->getOrCreateStateSet()->setMode( GL_CULL_FACE, osg::StateAttribute::OFF );"

AFTER:
"// clip everything below water line
            _reflectionCamera=renderToTexturePass( reflectionTexture.get() );
            _reflectionCamera->setClearColor( osg::Vec4( 0.0, 0.0, 0.0, 0.0 ) );
            _reflectionCamera->setCullMask( _reflectionSceneMask );
            _reflectionCamera->setCullCallback( new CameraCullCallback(this) );
            _reflectionCamera->getOrCreateStateSet()->setMode( GL_CLIP_PLANE0+0, osg::StateAttribute::ON );
            _reflectionCamera->getOrCreateStateSet()->setMode( GL_CULL_FACE, osg::StateAttribute::OFF );
            _reflectionCamera->getOrCreateStateSet()->setAttributeAndModes(new osg::FrontFace(osg::FrontFace::CLOCKWISE), osg::StateAttribute::ON | osg::StateAttribute::PROTECTED);"

The fix is also working, if the front and backface are drawn normally and it 
should also be helpfull if the backface is not drawn at all.

Original issue reported on code.google.com by marcel.p...@googlemail.com on 2 Jan 2012 at 2:50

Attachments:

• Reflection.png