Hello Carsten,
thank you for your detailed answer. It definitely made things clearer to
me. I have wrapped the setup for the scene render and post process with
push/popPartition() commands and things look better.
However, it seems that the contents of the FBO is not cleared between
consecutive frames. How can i schedule a glClearColor(...); glClear(...);
after the FBO is bound and before a call to recurseFromThis()?
I looked at the code of the RenderPartition class and the
OSG::RenderPartition::setupExecution() function calls
_pBackground->clear(&_oDrawEnv); if the RenderPartition::BackgroundSetup
flag is set. Therefore i tried:
DepthPeelingStage::renderEnter()
{
//init setup similar to HDRStage implementation
pPart->setRenderTarget(<myFBO>);
pPart->setBackground(pBack);
pPart->addSetupModeBit(RenderPartition::BackgroundSetup);
//if not first pass pushState() and add stage overrides here
recurseFromThis(renderAction);
//popState(), popPartition(), schedule postProcess, etc.
}
But this shows no effect i.e. the contents is still not cleared. Any idea?
Regarding the EXT_shader_image_load_store extension it requires OpenGL 3.0
and GLSL 1.30 unfortunately, see
http://developer.download.nvidia.com/opengl/specs/GL_EXT_shader_image_load_store.txt
Can i still use the mechanism you described for getting the function pointer?
Thanks.
Kind regards,
Alexander Lang
> Hello Andreas,
>
> On 09/11/2012 07:35 AM, Alexander Lang wrote:
>> 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);
>
> possibly a typo, but pPart->dropFunctor(f); is missing here, otherwise
> the post processing is not being run.
>
>> 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()?
>
> yes, keep in mind though that during scene traversal (i.e. when
> renderEnter() is called) nothing is actually drawn, only the partitions
> are set up and the work they are to do at draw time is specified.
>
>> - Why is the SimpleCallback required?
>
> see above, the actual work is done after scene traversal, so you need to
> delay work until then.
>
>> Could postProcess not be called
>> directly within renderEnter()? When is the callback executed in regards
>> to
>> the for-loop?
>
> every iteration of the loop must create a new partition, using
> pushPartition() and then getActivePartition() to get a pointer to it and
> set things like the FBO etc.
>
>> - What does a RenderPartition do?
>
> a render partition is a pass or a chunk of work to be done when objects
> are drawn.
>
>> When do you have to call
>> beginPartitionGroup() and pushPartition()?
>
> pushPartition() creates a new partition, so you need to call it when you
> start a new pass. Partitions are normally processed in reverse order
> from when they are created, if you begin a group the partitions in the
> group are processed in the order they are created in.
>
>> 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()
>
> each pass needs to be a partition, otherwise state sorting will draw
> objects in whatever order it deems most efficient without respecting
> pass boundaries.
>
>> - 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);
>
> IIRC that should make the texture available in texture unit 0.
>
>> 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 class id is not the texture unit; class id + 0 is texture unit 0,
> class id + 1 is texture unit 1, etc. (at least that's what it used to be).
>
>> - The HDR stage and others use direct OpenGL calls. Can any FC
>> implementation call arbitrary OpenGL functions that work in a
>> distributed
>> environment?
>
> OpenSG does not contain crystal ball technology ;) You have to know what
> you are doing and in particular be careful to reset any state you
> change, otherwise OpenSG's state tracking is going to be confused and
> you get "interesting" result.
>
>> 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.
>
> Is there an OpenGL extension that makes glBindImageTexture() available
> in OpenGL 2 contexts?
> If so, you can add prototypes for the extension to
> Source/Base/Base/OSGGLFuncProtos.h
> Add a static UInt32 _extSomeExtension extension id to your stage.
> Add for each function added by the extension static UInt32
> FuncIdBindImageTexture extension function ids to your stage.
> You register the extension and extension functions in
> DepthPeelingStage::initMethod() - see
> Source/System/State/Shader/Base/OSGShaderProgram.cpp for an example.
> To call such an extension function you place a line like:
>
> OSGGETGLFUNCBYID_GL3_ES(glCreateShader,
> osgGlCreateShader,
> FuncIdCreateShader,
> pWin);
>
> before you call it, to get a function pointer that is valid for the
> current context and then use osgGlCreateShader() as if it was
> glCreateShader() - again OSGShaderProgram.cpp has example usage.
>
> Cheers,
> Carsten
>
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