Re: [osg-users] draw callbacks

[Robert Milharcic]

You can use osgFX node kit framework to implement described capping tehnique. 
You do that by inheriting osgFX::Effect class. In your derived class you have 
to override/implement  virtual bool define_techniques() member of the 
osgFX::Effect class  like this:

 bool CappingEffect::define_techniques()
{
    CappingTechnique* technique = new CappingTechnique(this);
    addTechnique(technique);
    return true;
}

CappingTechnique must inherit from osgFX::Technique. In the derived class you 
will have to  implement virtual bool validate(osg::State&) const, virtual void 
define_passes() and optionally virtual osg::Node* getOverrideChild(int pass) 
like this:

bool CappingTechnique::validate(osg::State&) const
{
                return true;
}

bool CappingTechnique:: define_passes()
{
    // pass #1
    {
        osg::ref_ptr<osg::StateSet> ss = new osg::StateSet;
       ... setup states for  stencil operation
        addPass(ss.get());
    }
    // implement pass #2
    {
        osg::ref_ptr<osg::StateSet> ss = new osg::StateSet;
       ... setup states for solid color draw
        addPass(ss.get());
    }
}

You can optionally implement getOverrideChild (int pass) to supply some other 
graph for a particlular pass. You then add your group to the CappingEffect (the 
osgFX::Effect inherits from osg::Group node) and CappingEffect  to the camera.

Robert Milharcic

From: osg-users-boun...@lists.openscenegraph.org 
[mailto:osg-users-boun...@lists.openscenegraph.org] On Behalf Of Javier Taibo
Sent: Thursday, September 02, 2010 1:09 PM
To: osg-users@lists.openscenegraph.org
Subject: [osg-users] draw callbacks

  Hi,

  I have some solid geometry clipped by some clipping planes in an OSG 
application. I am trying to use the capping technique described in chapter 10 
of the Red Book using the stencil buffer. I have successfully implemented this 
technique in raw OpenGL, but I would like to use it whithin the OSG 
application. The technique is based on storing on the stencil buffer the 
regions that are "open" and then in a later pass draw a solid color in these 
regions.

  I have put the clipped geometry under an osg::Camera node with the stencil 
function configured. To do the second pass (the one that draws the caps in the 
regions marked in the stencil), I am trying to use a post-draw callback with 
the OpenGL calls (saving and restoring the states to avoid breaking things). 
The problem is that I need to set the NESTED rendering order to see all the 
scene graph, and when I do it, the post-draw callback is not called anymore.

  I do not have full control over the application, so the solution I am looking 
for has to be "transparent" to the rest of the scene graph. I must activate 
this behaviour to a group in the scene graph without breaking anything outside 
this branch.  What is the best way to do it? camera post-draw callbacks? 
rendering bins? any other?

  I am not very familiar with render passes in OSG, so the way I am trying is 
probably not the best way. I would appreciate any suggestion, advice or pointer 
to any related documentation or source code.


  Thanks in advance.


  Javier Taibo.

<<attachment: Robert Milharcic.vcf>>

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