Hi Sergey I would like to understand exactly how the graphics pipeline works and am struggling to figure this out by digging through the code (are there free books that deal with OSG and its implementation details in-depth? I dont mean the QSG by Paul Martz...). Also, my understanding of OpenGL is lacking in some places especially in implementation details so perhaps this will help clear things up for me.
In the prerender example we have something like this: 0: camera->setRenderTargetImplementation(osg::Camera::FRAME_BUFFER_OBJECT); 1: camera->attach(osg::Camera::BufferComponent(osg::Camera::COLOR_BUFFER0), image); 2: camera->setPostDrawCallback(new MyCameraPostDrawCallback(image)); 3: textureRect[tex_to_get]->setImage(0, image); As far as I understand this works as follows 0: This generates an FBO which has no data storage until I attach data storage to it (next step) ? Is this true? What happens then when I attach a color attachment but dont attach a depth buffer attachment? Does OSG automatically generate one for me? I ask because in regular OpenGL when you dont attach a depth attachment to an FBO then rendering to the FBO using glEnable(GL_DEPTH_TEST) produces incorrect results... 1: The image attached to the camera is the data storage for the FBO created in step 0. If this is the case then it means the FBO sits in RAM and not on the GPU. Is that true? 2:Here we set a post render callback using the image as our input. As far as I understand this means that the image (which is sitting in RAM) is edited in place. That means that as long as we dont need the data for actual rendering then we are being efficient because we dont copy to the GPU. Which brings up the next line... 3: We specify that a texture has the image as its image. I dont entirely understand what this means. When we create the original texture then OpenGL allocates space on the GPU for that texture. By using setImage(0,image) then does that mean that whatever is in that image (which sits on RAM) must always be copied to the GPU texture before the texture can be used at render time? All in all I feel quite confused and would like to understand how to do the above process efficiently. Ideally I would like to : pass dynamic geometry to the GPU every frame and have that rendered to textures inside the GPU. Occassionally I would like to ask the GPU to send the RTT textures back to the CPU, update them on the CPU and then send them back to the GPU. How should I be doing that in the most efficient way possible? Thank you! Cheers, aaron ------------------ Read this topic online here: http://forum.openscenegraph.org/viewtopic.php?p=41103#41103 _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
