Hello,
referring to an earlier question of mine on how to implement multi-pass
rendering for Depth-Peeling i followed your advice and created a custom
stage core similar to the HDR stage.
I looked at the source and tried to come up with an implementation but i
did not succeed in getting it to work.
Basically it looks like this:
DepthPeelingStage::renderEnter(Action* action)
{
beginPartitionGroup
pushPartition
//init similar to HDR implementation
setRenderTarget(myFBO)
renderPartition->setBackground(background);
background->clear()
//initialize depth buffer: draw Scene
this->recurseFromThis()
for (number of passes)
{
setRenderTarget(myOtherFBO)
setBackground(...)
background->setAlpha(...)
background->clear()
renderPartition->pushState()
//set new state for pass i: add blend, texture and depth chunks
renderPartition->addOverride(...)
this->recurseFromThis()
renderPartition->popState()
//Post process: draw quad textured with contents of this pass
//similar to HDR stage implementation
pushPartition()
//setup projection
RenderPartition::SimpleDrawCallback f;
f = boost::bind(&DepthPeelingStage::postProcess,
this, _1);
popPartition()
}
popPartition
endPartitionGroup
}
DepthPeelingStage::postProcess(DrawEnv*)
{
//get data
//activate FBO if not final
//activate material state
//draw quad with glBegin()/glEnd()
//deactivate material state
//deactivate FBO
}
With this setup the scene gets rendered to a texture which is displayed by
the quad but i do not see effects of other passes.
Therefore, i have several questions, hopefully you could help me
understand the internals of OpenSG better:
- Does this sound like a valid setup with the main work done in
renderEnter()?
- Why is the SimpleCallback required? Could postProcess not be called
directly within renderEnter()? When is the callback executed in regards to
the for-loop?
- What does a RenderPartition do? When do you have to call
beginPartitionGroup() and pushPartition()? Does each render pass have to
be wrapped in such a pair or does it suffice to call these at the begin
and end of renderEnter()
- How could i have a texture that is set up within this stage available in
the shader code of the user? I tried:
pRenderPartition->addOverride(pTextureObjChunk->getClassId(),
pTextureObjChunk);
followed by the call to recurseFromThis() but this showed no effect. I
replaced pTextureObjChunk->getClassId() with 0 or 1 since i assumed this
would set the texture unit but that did not work either.
- The HDR stage and others use direct OpenGL calls. Can any FC
implementation call arbitrary OpenGL functions that work in a distributed
environment?
I look forward to any answer. My concern is to have a way to correctly
display transparent geometry within OpenSG.
As a last note, what is required to integrate new OpenGL functions into
OpenSG? More specifically if the functionality of glBindImageTexture() was
available in OpenSG, the A-Buffer algorithm (see Cyril Crassin's approach:
http://blog.icare3d.org/2010/06/fast-and-accurate-single-pass-buffer.html)
could be used and multiple render passes would not be required any longer
for correct transparency.
Thanks.
Kind regards,
Alexander Lang
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