[osg-users] How to handle cameras in the scene graph when rendering to framebuffer

[Werner Modenbach]

Hi Robert,

sorry for the delayed answer. It's carnival time here and so everybody
is out - except me ;-)

I try to give an as compressed description as possible here.

The scene looks like that:
     *

* ---------------

*|RootNode|

*---------------

*/\

*------------------------------------

*|ShadowScene||evtl.PPU-Prozessor|

*------------------------------------

*/\

*------------------------------

*|Switchnode||LightSource|

*------------------------------

*/\\\

*--------------------------------

*|User scene||evtl.further|

*---------------|Objects |

* ----------------- The further objects are the wallpaper, a magnifier etc.


The main camera is a standard camera with perspective view and a
trackball manipulator.
The wallpaper class is like that:
classCl_3D_Wallpaper:publicosg::Camera{

public:

Cl_3D_Wallpaper(Cl_3Dview_osg*_parent);

/**This Method creates the background image. */

voidsetWallpaper(constQString_path);

protected:
Cl_3Dview_osg*view;
QStringpath;
};


Cl_3D_Wallpaper::Cl_3D_Wallpaper(Cl_3Dview_osg*_parent):view(_parent),path(QLatin1String("")){


setCullingActive(false);

setClearMask(0);

setAllowEventFocus(false);

setReferenceFrame(osg::Transform::ABSOLUTE_RF);

setRenderOrder(osg::Camera::POST_RENDER);

setProjectionMatrix(osg::Matrix::ortho2D(0.0,1.0,0.0,1.0));

setName(getNodeName().toStdString().c_str());

osg::StateSet*ss=getOrCreateStateSet();

ss->setMode(GL_LIGHTING,osg::StateAttribute::OFF);

ss->setAttributeAndModes(newosg::Depth(osg::Depth::LEQUAL,1.0,1.0));

view->installDefaultShader(ss);	// In case we are on gl3

}

/**DieseMethodeerzeugteineHintergrundbildanzeige,

*fallsderPfadaufeineBilddateiverweist.

*/

voidCl_3D_Wallpaper::setWallpaper(constQString_path){

          path=_path;

if(!_path.isEmpty()){

//================================================

//DieSzenedesBildeserzeugen

//================================================

osg::Geode*geode=newosg::Geode();

osg::Geometry*geometry=osg::createTexturedQuadGeometry(osg::Vec3(0,0,0),osg::Vec3(1,0,0),osg::Vec3(0,1,0),0,0,1,1);

geode->addDrawable(geometry);

osg::Texture2D*texture=view->loadTexture(_path,false);

geode->getOrCreateStateSet()->setTextureAttributeAndModes(BASE_TEXTURE_UNIT,texture,osg::StateAttribute::ON);

geode->getOrCreateStateSet()->setMode(GL_LIGHTING,osg::StateAttribute::OFF);

addChild(geode);

view->installDefaultShader(geode->getOrCreateStateSet());	//In case we are on gl3

}

}

Now the part of getting a frame buffer screenshot:

/**The screen image is rendered at a pregiven dpi*/

QImageCl_3Dview_osg::getHighResQImage(constint_dpi){

doublescale=(double)_dpi/(double)dpi;

//Calculation of image size and tiles per row

intwidth=(int)(view->getGraphicsWidth());

intheight=(int)(view->getGraphicsHeight());

intimageWidth=(int)(width*scale);

intimageHeight=(int)(height*scale);

inttiles=(imageWidth-1)/width+1;

         osg::ref_ptr<osg::Image>image=newosg::Image;


//Creating the new camera
    osg::ref_ptr<osg::Camera>  camera=newosg::Camera;

camera->getOrCreateStateSet()->setGlobalDefaults();

camera->setClearColor(view->getCamera()->getClearColor());

camera->setViewport(newosg::Viewport(0,0,width,height));

camera->setClearMask(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

camera->setReferenceFrame(osg::Transform::ABSOLUTE_RF);

camera->setRenderTargetImplementation(osg::Camera::FRAME_BUFFER_OBJECT);

camera->setRenderOrder( osg::Camera::POST_RENDER); camera->addChild(view->getCamera()->getChild(0));	// The root node

osg::ref_ptr<osg::Image>fbImage=newosg::Image;

fbImage->allocateImage(width,height,1,GL_RGBA,GL_UNSIGNED_BYTE,1);

camera->attach(osg::Camera::COLOR_BUFFER,fbImage.get(),0,0);

//Setting the new camera a child of the main camera

         view->getCamera()->addChild(camera.get());

//Loop over tiles
    osg::MatrixdviewMatrix=view->getCamera()->getViewMatrix();

osg::MatrixdprojectionMatrix=view->getCamera()->getProjectionMatrix();

          inty_out=imageHeight-1;

for(introw=0;row<tiles;row++){

                   for(intcol=0;col<tiles;col++){

//Calculateprojectionmatrixoffsetofeachtile

osg::MatrixoffsetMatrix=

osg::Matrix::scale(scale,scale,1.0)*

osg::Matrix::translate(scale-1-2*col,scale-1-2*row,0.0);

camera->setViewMatrix(viewMatrix);

camera->setProjectionMatrix(projectionMatrix*offsetMatrix);

view->frame();
image=fbImage.get();

//Transferring tile into final image
	    .......

                   }

y_out-=height;

if(y_out<0)break;

}

view->getCamera()->removeChild(camera.get());
}


The rendered image is missing my wallpaper.
If I add the camera as a slave camera to the main camera I just get an
empty black image.
Actually I also don't understand the difference between slave and child
cameras here. I know you explained it recently :-)
Why does the slave camera give an empty image but the child camera doesn't?

BTW. I wrote my code here with the background of giving an example to
others looking for functionality like that.




Am 24.02.2017 um 17:56 schrieb Robert Osfield:
> Hi Werner,
>
> In principle what you are doing should be possible.  What is going
> wrong in your instance is impossible to say without seeing how you are
> setting up the viewer Camera's and the in scene graph Camera's.
>
> Robert.
>
> On 24 February 2017 at 16:44, Werner Modenbach
> <Werner.Modenbach at texion.eu> wrote:
>> Hi all,
>> sorry for so many questions today.
>>
>> My scene graph has additional cameras as children somewhere in the scene
>> graph.
>> For example a hud camera for a background image.
>>
>> I do screenshots by adding a slave camera to the main camera which renders
>> the scene to the FB.
>> Unfortunately this rendering doesn't show the parts of the nested cameras,
>> i.e. no
>> background wallpaper.
>> What is the recommended way to solve this?
>>
>> Thanks for any help.
>>
>> - Werner -
>>
>>
>> _______________________________________________
>> osg-users mailing list
>> osg-users at lists.openscenegraph.org
>> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
> _______________________________________________
> osg-users mailing list
> osg-users at lists.openscenegraph.org
> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openscenegraph.org/pipermail/osg-users-openscenegraph.org/attachments/20170227/50b2b679/attachment-0003.htm>