[osg-users] Rendering double triangles as one quad

[OpenSceneGraph Users]

>
> Hello!
>

I will post my solution to this in case someone is interested.

I solved it by having two different geometries controlled by one switch 
node, and depending on the rendermode i control which one is visible.


void OsgSceneMesh::constructVertexAttribute(GI::SceneMesh* sceneMesh, osg::Geode* geode, osg::Geometry* geometry, bool constructSkeletonMesh)    
{
    osg::ref_ptr<osg::Vec3Array>    vertices = new osg::Vec3Array();

    osg::ref_ptr<osg::Vec3Array>    normals = new osg::Vec3Array();

    osg::ref_ptr<osg::Vec2Array>    texCoords  = new osg::Vec2Array();

    osg::ref_ptr<osg::Vec2Array>    texCoords2  = new osg::Vec2Array();


    osg::ref_ptr<osg::DrawElements> indices;


    if(constructSkeletonMesh) indices = static_cast<osg::DrawElements*>(new osg::DrawElementsUShort(GL_LINE_LOOP));

    else indices =  static_cast<osg::DrawElements*>(new osg::DrawElementsUShort(

                                sceneMesh->getType() == GI::MeshType::LINE ?  GL_LINES : GL_TRIANGLES));


    osg::ref_ptr<osg::Vec4Array>    vertexColor = new osg::Vec4Array;


    std::vector<long unsigned int> sceneMeshIndices = sceneMesh->getIndices();

    std::vector<GI::Vertex> sceneMeshVertices = sceneMesh->getVertices();


    //push in vertices

    for(const auto & vertex : sceneMeshVertices)

    {

        vertices->push_back(osg::Vec3(vertex.x_, vertex.y_, vertex.z_));

        normals->push_back(osg::Vec3(vertex.nx_, vertex.ny_, vertex.nz_));

        texCoords->push_back(osg::Vec2(vertex.u_, vertex.v_));

        texCoords2->push_back(osg::Vec2(vertex.u_, vertex.v_));

        vertexColor->push_back(osg::Vec4(vertex.r_,vertex.g_,vertex.b_, 1.f));

    }


    //push in indices

    for(const auto & index : sceneMeshIndices)

    {

        indices->addElement(index);

    }


    //texture buffer and color values later

    geometry->setVertexArray(vertices.get());

    geometry->setNormalArray(normals.get(), osg::Array::BIND_PER_VERTEX);

    geometry->setTexCoordArray(0, texCoords, osg::Array::BIND_PER_VERTEX);

    geometry->setTexCoordArray(1, texCoords2, osg::Array::BIND_PER_VERTEX);

    geometry->setColorArray(vertexColor.get(), osg::Array::BIND_PER_VERTEX);

    geometry->addPrimitiveSet(indices.get());


    geode->addDrawable(geometry);
}



the render mode is controlled through this function 

void OsgSceneMesh::updateRenderMode(GI::PolygonMode polygonMode)

{

    if(this->getNumChildren() < 2) return; //this means we havent initialized the mesh yet


    //set enable/disable skeleton mesh only at wireframe quad polygonmode

    // 0 == skeleton mesh, 1 == triangle mesh


    osg::PolygonMode * osgPolygonMode = new osg::PolygonMode;


    switch(polygonMode)

    {

        case GI::PolygonMode::SOLID :

        {

            this->setValue(0, true);

            this->setValue(1, false);

            osgPolygonMode->setMode( osg::PolygonMode::FRONT_AND_BACK, osg::PolygonMode::FILL);

            triangleMeshVisible_ = true;

            break;

        }

        case GI::PolygonMode::WIREFRAME_TRIANGLE :

        {

            this->setValue(0, true);

            this->setValue(1, false);

            osgPolygonMode->setMode( osg::PolygonMode::FRONT_AND_BACK, osg::PolygonMode::LINE);

            triangleMeshVisible_ = true;

            break;

        }

        case GI::PolygonMode::WIREFRAME_QUAD :

        {

            this->setValue(0, false);

            this->setValue(1, true);

            osgPolygonMode->setMode( osg::PolygonMode::FRONT_AND_BACK, osg::PolygonMode::FILL);

            triangleMeshVisible_ = false;

            break;

        }

    }


    this->getOrCreateStateSet()->setAttributeAndModes( osgPolygonMode,

    osg::StateAttribute::OVERRIDE | osg::StateAttribute::ON );

}


This works fine except for one thing, my intersection raycaster does not 
handle the LINE LOOP mesh when the triangle node is switched off. 

I solved it by creating a node visitor

OsgGeodeMeshActivatorVisitor::OsgGeodeMeshActivatorVisitor(const bool& isReset) :

    isReset_(isReset)

{

    this->setTraversalMode(osg::NodeVisitor::TraversalMode::TRAVERSE_ALL_CHILDREN);

}

void OsgGeodeMeshActivatorVisitor::apply(osg::Node& node)

{

    switchGeodeVisibility(node);

}


void OsgGeodeMeshActivatorVisitor::switchGeodeVisibility(osg::Node& node)

{

    osg::Group* group = node.asGroup();

    if ( !group ) return;


    if(group->getNumChildren() == 0) return;

    for ( unsigned int i=0; i<group->getNumChildren(); ++i )

    {

        OsgSceneMesh* osgSceneMesh = dynamic_cast<OsgSceneMesh*>(group->getChild(0));

        if(osgSceneMesh)

        {

            if(isReset_)  osgSceneMesh->resetTriangleMeshVisible();

            else osgSceneMesh->forceTriangleMeshVisible();


        }

        switchGeodeVisibility(*group->getChild(i));

    }

}



which can force triangle mesh visibility on and reset to original value.

Now in my intersection algorithm i simply force visibility on by accepting 
the visitor on the root node in my tree.

osg::ref_ptr<osgUtil::LineSegmentIntersector> intersector

            = new osgUtil::LineSegmentIntersector( osgUtil::Intersector::WINDOW, mousePosition.x(),  viewportModel_->getHeight() - mousePosition.y());




    osgUtil::IntersectionVisitor intersectionVisitor ( intersector.get() );

    intersectionVisitor.setTraversalMask( ~0x1 ); // mask, things that we dont want to be selected sets 0x1


    osg::Camera* osgCamera = viewer_->getCamera();


    OsgGeodeMeshActivatorVisitor geodeVisibilitySwitchOn(false);

    OsgGeodeMeshActivatorVisitor geodeVisibiltyReset(true);


    osg::Node* root = viewer_->getSceneData();


    root->accept(geodeVisibilitySwitchOn);


    if(osgCamera) osgCamera->accept( intersectionVisitor );

    else

    {

        root->accept(geodeVisibiltyReset);

        return rayTracedMeshPairVector;

    }


    root->accept(geodeVisibiltyReset);


    if( !intersector->containsIntersections() )

    {

        return rayTracedMeshPairVector;

    }

    else

    {

      //work with result, not included in this demo

       }



 And thats it, now we have the possibility to render triangulated wireframe , quaded wireframe and solid structures while intersection with the meshes are possible. here is an image of the result..


https://imgur.com/a/hFh6aGm




Have a good day


//Dan



 

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