Hi,

I can't help you with your specific drawable question, but what would you like to achieve? In the osggameoflife example there is an example of ping-pong using multiple cameras and switches. You can also swap output textures if they are exactly the same using a callback. See here for inspiration:
http://code.google.com/p/flitr/source/browse/trunk/examples/keep_history_pass/keep_history_pass.cpp

cheers
jp

On 28/09/2011 10:45, Emmanuel Roche wrote:
Hi everyone,

I'm trying to setup an pure OpenGL FBO with render to texture target in
an OSG drawable. But I just can't figure out how to do that "properly"
(eg. how to "isolate those pure openGL calls from the rest of the OSG
scene).

in my drawa implementation I just have:

virtual void drawImplementation(osg::RenderInfo& info) const
{
     OSG_NOTICE << "Drawing PingPongDrawable...";

     osg::State* state = info.getState();
     const unsigned int contextID = state->getContextID();

     if(!_initialized && !init(contextID,*state)) {
         OSG_WARN << "Failed FBO setup!";
         return;
     }

     state->checkGLErrors("end of PingPongDrawable drawing.");
}

So i'm really just calling an "init" function once to jus try to
_create_ an FBO... I didn't even start using it..., the code of the init
function is as follow:

bool init(unsigned int contextID, osg::State& state) const {

     const FBOExtensions* fbo_ext =
FBOExtensions::instance(contextID,true);
     const osg::Texture2DArray::Extensions* t2darray_ext =
osg::Texture2DArray::getExtensions(contextID,true);

     // Push attribs to avoid collisions with existing OSG scene ?
     glPushAttrib(GL_VIEWPORT_BIT | GL_COLOR_BUFFER_BIT | GL_TEXTURE_BIT
| GL_ENABLE_BIT);

     state.checkGLErrors("Before PPD init.");

     // Prepare the target texture for the FBO:
     state.setActiveTextureUnit(1);
     state.checkGLErrors("Activating texture slot 1");

     int FFT_SIZE=256;

     GLuint fftaTex = 0;
     glGenTextures(1, &fftaTex);
     glBindTexture(GL_TEXTURE_2D_ARRAY_EXT, fftaTex);
     glTexParameteri(GL_TEXTURE_2D_ARRAY_EXT, GL_TEXTURE_MIN_FILTER,
GL_LINEAR_MIPMAP_LINEAR);
     glTexParameteri(GL_TEXTURE_2D_ARRAY_EXT, GL_TEXTURE_MAG_FILTER,
GL_LINEAR);
     glTexParameteri(GL_TEXTURE_2D_ARRAY_EXT, GL_TEXTURE_WRAP_S, GL_REPEAT);
     glTexParameteri(GL_TEXTURE_2D_ARRAY_EXT, GL_TEXTURE_WRAP_T, GL_REPEAT);
     glTexParameterf(GL_TEXTURE_2D_ARRAY_EXT,
GL_TEXTURE_MAX_ANISOTROPY_EXT, 16);
     t2darray_ext->glTexImage3D(GL_TEXTURE_2D_ARRAY_EXT, 0,
GL_RGBA16F_ARB, FFT_SIZE, FFT_SIZE, 5, 0, GL_RGBA, GL_FLOAT, NULL);
     fbo_ext->glGenerateMipmap(GL_TEXTURE_2D_ARRAY_EXT);
     state.checkGLErrors("preparing target texture");


     // Initialize the FBO
     fbo_ext->glGenFramebuffers(1, &_fftFbo);
     state.checkGLErrors("Generating FBO");


     fbo_ext->glBindFramebuffer(GL_FRAMEBUFFER_EXT, _fftFbo);
     state.checkGLErrors("Bind Framebuffer in init.");
#ifdef ATTACH_TEXTURE
     fbo_ext->glFramebufferTexture(GL_FRAMEBUFFER_EXT,
GL_COLOR_ATTACHMENT0_EXT, fftaTex, 0);
     state.checkGLErrors("FramebufferTexture setup");
#endif
     GLuint fboId = state.getGraphicsContext() ?
state.getGraphicsContext()->getDefaultFboId() : 0;
     fbo_ext->glBindFramebuffer(GL_FRAMEBUFFER_EXT, fboId);


     if(fbo_ext->glCheckFramebufferStatus(GL_FRAMEBUFFER_EXT) !=
GL_FRAMEBUFFER_COMPLETE_EXT) {
         OSG_WARN << "Error while setting up Pingpong FBO.";
     }

     state.checkGLErrors("end of Framebuffer settings");

     glBindTexture( GL_TEXTURE_2D_ARRAY_EXT, 0 );

     glPopAttrib();

     _initialized = true;
     return true;
}

Adding such a drawable in my scene, i don't have any problem as long as
ATTACH_TEXTURE is *undefined*. But when I define this, I still don't
have any error reported by the drawable itself (all the checkGLErrors I
inserted). But then getcontinous list of

" Warning: detected OpenGL error 'invalid operation' at after
RenderBin::draw(..)" messages :-(

=> Any idea what I'm doing wrong here ? How can I "enforce" the
isolation between those openGL calls and what's left from the OSG scene
? after all, since this init function is called only once, there should
not be any continous warning report if it didn't have a side effect
outside of this drawable encapsulation...


Thanks for you help !! I really feel desperated now... :'(

Manu.





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