[osg-users] [osgPPU] X-ray Design use of OsgPPU
Hi, I'm trying to come up with a design using OSG to build what i'm calling an X-ray viewer. Basically i have relatively simple geometry, a shell or skin of a vehicle and then the interior. I want to view the interior as penetrated by the X-rays, which is based on a thickness calculation and a distance and aspect angle, all hopefully done in shaders. I envision the shaders setting the fragment alpha and/or color when rendering the shell, then after to render the interior and combine with the shell texture to create the final view, showing through the interior in desired parts. Finally, i desire to get a histogram of the colors of the interior to see how the shell performed on the x-rays with the interior. Do you see this as an appropriate application / use of osgppu? i'm running osg 2.8.1. will ppu work with that. i've got osgppu 0.4 i think. also, i'm thinking i need to create the ppu nodes programmatically instead of reading ppu files, so i need examples of that type. i'm just starting to look through them. Thank you! Cheers, Bob -- Read this topic online here: http://forum.openscenegraph.org/viewtopic.php?p=16090#16090 ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] [osgPPU] X-ray Design use of OsgPPU
Hi Bob, huh, I would say it depends on your implementation. Currently the way you describe it requires a volumetric rendering approach. The thickness calculation seems to be the most tricky part. If you have your volume data, then use osgVolume for that (I haven't tested it, so I do not know how well it suits your expectations). Other possible solution is to render all your triangles in slices which are perpendicular in viewing direction. So you specify clip planes and render your model in several passes. Of course no backface culling or any other culling except of this clip planes should be active. So you render your slices into a several textures (actually you only need depth values). Using osgPPU you combine all that textures and compute thickness. After all passes (depends on complexity of your model, how much passes you want to use), i.e. 128 passes, you will have as result thickness of each pixel in viewing direction. This thickness texture can then be projected on the model in your scene back. Since hte projection is from the view point, you shouldn't see any big artifacts. So this is a way, how I would try to do it. Maybe there exists better approaches. Cheers, art ryoumans wrote: Hi, I'm trying to come up with a design using OSG to build what i'm calling an X-ray viewer. Basically i have relatively simple geometry, a shell or skin of a vehicle and then the interior. I want to view the interior as penetrated by the X-rays, which is based on a thickness calculation and a distance and aspect angle, all hopefully done in shaders. I envision the shaders setting the fragment alpha and/or color when rendering the shell, then after to render the interior and combine with the shell texture to create the final view, showing through the interior in desired parts. Finally, i desire to get a histogram of the colors of the interior to see how the shell performed on the x-rays with the interior. Do you see this as an appropriate application / use of osgppu? i'm running osg 2.8.1. will ppu work with that. i've got osgppu 0.4 i think. also, i'm thinking i need to create the ppu nodes programmatically instead of reading ppu files, so i need examples of that type. i'm just starting to look through them. Thank you! Cheers, Bob -- Read this topic online here: http://forum.openscenegraph.org/viewtopic.php?p=16098#16098 ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] [osgPPU] X-ray Design use of OsgPPU
Hi, for the thickness it's actually a fixed data for the geometry (not really thickness). It's only thickness in the analogue of the x-ray model. It's geometry dependent data, and for starting out adding this data item and/or having only the one value will do. I'm just looking for the best design using osg. So with that, maybe osgVolume is not necessary. I have userdata and/or node callbacks to get this data for each geometry (e.g., Uniform callback for the vertex shader all using the same var name). I found your slicing idea in osgppu interesting. So, given this thickness as data and not requiring geometry calculation, how would you see going at it? Thank you! Cheers, Bob -- Read this topic online here: http://forum.openscenegraph.org/viewtopic.php?p=16106#16106 ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] [osgPPU] X-ray Design use of OsgPPU
Hello, ryoumans wrote: for the thickness it's actually a fixed data for the geometry (not really thickness). It's only thickness in the analogue of the x-ray model. It's geometry dependent data, and for starting out adding this data item and/or having only the one value will do. I'm just looking for the best design using osg. So with that, maybe osgVolume is not necessary. I have userdata and/or node callbacks to get this data for each geometry (e.g., Uniform callback for the vertex shader all using the same var name). OK, but your data must be view dependent. Otherwise how you would imagine to have X-ray like view, if you just have per vertex data? Or maybe I just don't really understand what you would like to have. I found your slicing idea in osgppu interesting. So, given this thickness as data and not requiring geometry calculation, how would you see going at it? Giving the thickness of data, I would render the object just as it is and using a shader, I would compute the viewing direction for each pixel (or vertex). Then having your view dependent data (so it would be probably a 6D data, for each position in each viewing direction. Or maybe 5D, for each position on surrounding sphere in each viewing direction) I would just compute color based on this thicknes. I do not see currently any other way of rendering X-ray like 3D models without having thickness data for each viewing direction and viewing position. THe way I proposed, is the way how one could compute this data on the fly. Maybe we can work out an example usng osgPPU so that other people can profit from it ;) cheers, art -- Read this topic online here: http://forum.openscenegraph.org/viewtopic.php?p=16110#16110 ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] [osgPPU] X-ray Design use of OsgPPU
Hello, Pardon me if I am jumping into the middle of this conversation, but XRay rendering has been done before. Look at shader examples from NVidia and others for volumetric fog and adapt them accordingly. The basic approach is to use the depth buffer and subtraction to render thickness as a bit field depth and then use that depth index for a lookup into your fog texture (1D) to produce the desired visual effect. Attenuation of the objects (different material parameters) can be achieved by setting values in texture units 1, 2 or 3 of the model (so you can still look at them visually). Modeling more advanced features of X-Ray light (non-linear falloff, for example) can be accomplished in the 1D lookup texture or it can be extended to a 2D or even 3D texture. Very realistic effects that mix with real objects can even be achieved. Hope that helps, - Paul On Aug 11, 2009, at 1:15 PM, Art Tevs wrote: Hello, ryoumans wrote: for the thickness it's actually a fixed data for the geometry (not really thickness). It's only thickness in the analogue of the x-ray model. It's geometry dependent data, and for starting out adding this data item and/or having only the one value will do. I'm just looking for the best design using osg. So with that, maybe osgVolume is not necessary. I have userdata and/or node callbacks to get this data for each geometry (e.g., Uniform callback for the vertex shader all using the same var name). OK, but your data must be view dependent. Otherwise how you would imagine to have X-ray like view, if you just have per vertex data? Or maybe I just don't really understand what you would like to have. I found your slicing idea in osgppu interesting. So, given this thickness as data and not requiring geometry calculation, how would you see going at it? Giving the thickness of data, I would render the object just as it is and using a shader, I would compute the viewing direction for each pixel (or vertex). Then having your view dependent data (so it would be probably a 6D data, for each position in each viewing direction. Or maybe 5D, for each position on surrounding sphere in each viewing direction) I would just compute color based on this thicknes. I do not see currently any other way of rendering X-ray like 3D models without having thickness data for each viewing direction and viewing position. THe way I proposed, is the way how one could compute this data on the fly. Maybe we can work out an example usng osgPPU so that other people can profit from it ;) cheers, art -- Read this topic online here: http://forum.openscenegraph.org/viewtopic.php?p=16110#16110 ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] [osgPPU] X-ray Design use of OsgPPU
Hi, yes view dependent ok. imagine a vehicle, each geode is a panel and the panel has a thickness. i plan to set a distance for the x-ray and a viewing angle (about z, assume constant elevation (about x or y), render a frame and see what interior geometry fraction shows through by counting the pixels as the ratio of num of colored pixels. for the next frame, the viewing angle and/or distance will change. Note that the distance only serves to effect the power (vs thickness) of the x-ray so that as the viewing pos is closer more penetration can occur. i would be interested in how to set this up as a multi-render ppu arrangement. My geometry is in a file, but there are several other nodes i create programmatically to make all this work. My problem is i'm very new with textures and shading and it's difficult to debug, compared to the usual development approach. right now i don't know the best way to set up the shader / texture / pixel objects. I'm ok with the osg nodes and have the transforms and callbacks ok. even the uniforms per geode are ok. i'm looking at depthpeeling and several other examples from osg to find the way to go with the shader pixel analysis parts. ... Thank you! Cheers, Bob -- Read this topic online here: http://forum.openscenegraph.org/viewtopic.php?p=16111#16111 ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
