[osg-users] How do cameras handle the render target?

[Sebastian Messerschmidt]

Hi Werner,


from diagonal reading:

You could make all cameras composing to the same FBO and get the texture 
in a final pass that can either put the image to Framebuffer or read 
back the texture. Also take a look at the screenshot example (using 
pbuffer) and the various draw callbacks.

Cheers
Sebastian


> Hi all.
>
> I have a problem understanding how cameras handle render targets.
> My special case:
> I have a standard camera on a view.
> The root node of the scene is a group with the following children:
>
> - my model
> - hud camera for wallpaper
> - hud camera for text
> - more cameras for special cases
>
> All the cameras are children of the group node and do POST_RENDER operation.
>
> I need snapshots of the complete scene from various camera positions.
> What I do:
>
> osg::ref_ptr<osg::Camera>camera=view->getCamera();
>
> osg::ref_ptr<osg::Image>fbImage=newosg::Image;
>
> fbImage->allocateImage(width,height,1,GL_RGBA,GL_UNSIGNED_BYTE,1);
>
> osg::Camera::RenderTargetImplementationrti=camera->getRenderTargetImplementation();
> camera->setRenderTargetImplementation(osg::Camera::FRAME_BUFFER_OBJECT);
> camera->attach(osg::Camera::COLOR_BUFFER,fbImage.get(),0,0);
> camera->dirtyAttachmentMap();
>
> Then I do snapshots with the modified projection matrix of the camera.
> After each snapshot I read the contents of the fbImage.
>
> I reset everything to the initial status by:
>
> camera->setRenderTargetImplementation(rti);
>
> camera->detach(osg::Camera::COLOR_BUFFER);
>
> camera->dirtyAttachmentMap();
>
>
> Unfortunately the fbImage always only contains my model but not the
> child cameras renderings.
> Attaching the fbImage to the child cameras as well gives me just a black
> fbImage.
> Of course the child cameras do not clear the color buffer.
>
> What is the proper way of receiving the complete rendering? I also tried
> already
> installing a slave camera to the main camera but that also gives me only
> the rendered model.
> And rendering to the fbImage by installing an additional child camera
> with POST_RENDER instead
> of a slave camera leads to the same result.
>
> Rendering to screen is perfect, but to fbImage is not.
> It seems I'm blind on some basic functionality and all my research
> doesn't open my eyes.
>
> I instantly hope for some help.
>
> Thanks
>
> - Werner -
>
>
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