[osg-users] Tesselation on Model

[Sebastian Messerschmidt]

Hi David,

tesselation shaders usually work on the GL_PATCH primitive rather than 
usual triangles. So in order to get your program running you need to run 
a visitor on the scene and convert the primitive sets to this.
This however won't magically solve every tesselation problem, but this a 
totally different domain.

See the attached apply for a nodevisitor. It will "work" in some cases. 
Be sure you have triangles in the source models (so no quads) beforehand.

     virtual void apply( osg::Geode& node )
     {

         for (size_t drawable_num =0; drawable_num < 
node.getNumDrawables();++drawable_num)
         {
             osg::Drawable* drawable = node.getDrawable(drawable_num);
             drawable->setUseDisplayList(false);
             drawable->setUseVertexBufferObjects(true);
             osg::Geometry* geom = drawable->asGeometry();
             if (!geom)
             {
                 continue;
             }
             for (size_t primset_num= 0; primset_num < 
geom->getNumPrimitiveSets(); ++primset_num)
             {
geom->getPrimitiveSet(primset_num)->setMode(osg::PrimitiveSet::PATCHES);
                 geom->getOrCreateStateSet()->setAttribute(new 
osg::PatchParameter(3));
             }
         }
         traverse(node);
     }

Cheers
Sebastian
> Hi osg-Forum,
>
> I'm kind of stuck with a problem in how to combine a tesslation shader in osg with a normal model right now. I really searched over google a couple of times and over the osg forum. I can't find an answer to my problem. Normally i prefer to not ask and just resolve it myself because thats my problem and not yours. As you can see this is my first post and i just registered here to ask that. I'm really sry for that.
>
> The thing is that I'm currently working on is an application that will just display a model. The model i'm working on is a huge bunch of GroupNodes that resolve down in the tree to geode-group-nodes and then geometrynodes. I guess thats pretty normal. With default osg shaders everty thing works nice and smooth.
>
> Now comes the problem. I have to tesselate the Model.
> I admit that im not used to programm shaders and only did it with DirectX 11. But the easy things worked back then.
> For this project i used the "osgtesselateshaders" example of yours and did just copy the shaders there. I know that now all the texture, material and own lightning won't work with this shaders. I just want to see if the wireframe will get tesselated. For that i create the osg::Program variable in a ref_ptr and then set the pointer of it to all geometrynodes of the model. Every Geometrynode will get his own uniform with "innerTesselation", "outerTesselation" variables and so own. I also created hotkeys for "+" and "-" that will change the values of all Geoemtrynode as pleased.
>
> The default shader of osg works perfectly fine with my programm but of course no tesselation will hapen. Now if i start the programm with the osg tesselateion shaders of "osgtesselateshaders" it will just print this in Visual Studio:
>
> "Warning: detected OpenGL error 'invalid operation' at after RenderBin::draw(..)"
>
> This warning pretty much says nothing as far as i have googeld it. Just says "some Problem ist here". Of course the viewer will show nothing of my model.
>
> So now my question what do i have to change to make the shaders of the example work with a loaded model? Is it even possible to make this example work with a model? Isn't a model just a bunch of triangles (+ texture and materials) as the Icosahedron in the example? Whats the difference here?
>
> It would be cool if somebody allready has an example on how to use an tesselation shader with a simpel model that he can (is allowed) to post here.
>
> I'm sry for the post if the problem is just a simple coding error.
>
>
> Code:
>
> // init of the programm
> this->mShader = new osg::Program();
> this->mShader->addShader(new osg::Shader(osg::Shader::VERTEX,			shader::Shader::vertSource));
> this->mShader->addShader(new osg::Shader(osg::Shader::TESSCONTROL,		shader::Shader::tessControlSource));
> this->mShader->addShader(new osg::Shader(osg::Shader::TESSEVALUATION,	shader::Shader::tessEvalSource));
> this->mShader->addShader(new osg::Shader(osg::Shader::GEOMETRY,			shader::Shader::geomSource));
> this->mShader->addShader(new osg::Shader(osg::Shader::FRAGMENT,			shader::Shader::fragSource));
> this->mShader->setParameter(GL_GEOMETRY_VERTICES_OUT_EXT, 3);
> this->mShader->setParameter(GL_GEOMETRY_INPUT_TYPE_EXT, GL_TRIANGLES);
> this->mShader->setParameter(GL_GEOMETRY_OUTPUT_TYPE_EXT, GL_TRIANGLE_STRIP);
>
> n->setShader(this->mShader.get());
>
>
>
>
>
> Code:
>
> void scene::GroupNode::setShader(osg::Program * p) {
> 	NodeIDMap::iterator itr;
> 	for (itr = this->mChildren.begin(); itr != this->mChildren.end(); ++itr)
> 		itr->second->setShader(p);
> }
>
>
>
>
>
> Code:
>
> void scene::GeometryNode::setShader(osg::Program * p) {
> 	auto *ss = this->mOSGNode->getOrCreateStateSet();
> 	ss->setAttribute(p);
> }
>
>
>
>
>
> Code:
>
> scene::GeometryNode::GeometryNode(osg::Geometry * ptrOSGNode) {
>    ....
>          this->mTessInnerU = new osg::Uniform("TessLevelInner", 1.0f);
> 	this->mTessOuterU = new osg::Uniform("TessLevelOuter", 1.0f);
>
> 	osg::StateSet * state;
> 	state = ptrOSGNode->getOrCreateStateSet();
> 	state->addUniform(new osg::Uniform("AmbientMaterial", osg::Vec3(0.04f, 0.04f, 0.04f)));
> 	state->addUniform(new osg::Uniform("DiffuseMaterial", osg::Vec3(0.0f, 0.75f, 0.75f)));
> 	state->addUniform(new osg::Uniform("LightPosition", osg::Vec3(0.25f, 0.25f, 1.0f)));
> 	state->addUniform(this->mTessInnerU.get());
> 	state->addUniform(this->mTessOuterU.get());
> 	state->setAttribute(new osg::PatchParameter(3));
> }
>
>
>
>
> Thank you!
>
> Cheers,
> NoxxKn[/code]
>
> ------------------
> Read this topic online here:
> http://forum.openscenegraph.org/viewtopic.php?p=66608#66608
>
>
>
>
>
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