Hi to compute depth from z-buffer depth you should use:
depth = -gl_ProjectionMatrix[3].z/(zb_depth * (-2.0) + 1.0 - gl_ProjectionMatrix[2].z) where: gl_ProjectionMatrix[3].z = - 2*far*near / (far - near) gl_ProjectionMatrix[2].z = - (far + near) / (far - near) Cheers. 14.09.2012, 00:49, "Andrey Shvartsman" <[email protected]>: > Hello, > > I am trying to read "real" distance from a depth buffer from a scene, and I > have a couple of questions. I am using Wang Rui's code as a starting point > for working with depth buffers (specifically his code from the OpenSceneGraph > Cookbook Chapter 6, Recipe 4). > > What I am trying to do is to read the distance from the depth buffer and dump > it to standard output as a start. I've attached an osg::Image to the viewer's > camera's depth buffer, and I am querying the image values during a click > event in a pick handler (the reason for the pick handler is I would like to > eventually do a comparison of the distance value I get from using an > Intersector vs the value from the depth buffer). > > Code: > > viewer.getCamera()->attach(osg::Camera::DEPTH_BUFFER,image); > > image->allocateImage(32,32,1,GL_DEPTH_COMPONENT,GL_FLOAT); > > So I am using a 32x32 image, and I am querying the image value with: > > Code: > > for(int k=0; k<32; k++) > { > for(int l=0; l<32; l++) > { > z_buffer=((float*)image->data(k,l))[0]; > z=-1/(z_buffer-1); > std::cout<<" "<<z<< " "; > } > std::cout<<std::endl; > } > > I understand that the z-buffer distance is not linear, so following the > article "Love your Z-Buffer" by Steve Baker (can't post links yet because I > don't have enough posts) I came up with the formula z=-1/(z_buffer-1) for > converting a z_buffer value to an approximate real distance value for a 24 > bit depth buffer, with zNear at 1m, and zFar at 10,000m > > However the values I am getting when querying the resulting image don't make > a lot of sense to me. When I am standing on my terrain in first-person mode, > visually I see the top half of my screen filled with the sky, and the bottom > half with the terrain, so I would expect to have very large distance values > for the top portion of the depth buffer image, and smaller and smaller values > as I get closer to the bottom. However all of the values in the 32x32 depth > image are around 2m. > > I would really appreciate it if someone could take a look at the code and let > me know where I am going wrong. > > Eventually, I would like to render the depth buffer as a grayscale image akin > to what you would see from a ranging sensor such as a lidar or a Kinect. Is > this even a good approach to do this kind of visualization or am I better of > trying some sort of a ray-tracing solution? My only concern with ray-tracing > is that I need to maintain "soft" real-time performance, and I am not sure > that I can achieve that using a ray-tracing solution. I would appreciate any > advise. > > Thank you! > > Andrey > > ------------------ > Read this topic online here: > http://forum.openscenegraph.org/viewtopic.php?p=50031#50031 > > _______________________________________________ > osg-users mailing list > [email protected] > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
