Re: [osg-users] Autoshadow aliasing in shadow maps
Hi all, Thanks for your posts, and sorry for my very late response. I´ve been on holidays and working in another things, so I left this issue abandoned. But finally, I could get rid of these artifacts, and therefore, solve my problem. Although the filters mitigated the effect, they were still noticeable and the performance was affected. But the solution that Robert proposed works almost perfectly for me! As Robert said, the key was to do the lighting calculations in the fragment shader, and multiply the shadow factor by the diffuse light component. After that, I can add the ambient light factor to achieve a well lighted surface. This solution is so easy conceptually and to implement that I´m mad at myself because I didn´t think about it ;) Thank you very much for your help, I think that this thread can be marked as solved. Cheers, Justo -- Read this topic online here: http://forum.openscenegraph.org/viewtopic.php?p=43038#43038 ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] Autoshadow aliasing in shadow maps
Hi Sergey, On Mon, Aug 29, 2011 at 10:55 PM, Sergey Polischuk pol...@yandex.ru wrote: All shadowmapping techniques have problems with such aliasing problems. You can try use shadow volumes technique as it dont suffer from this problem and generates correct shadows in any case, but it have other drawbacks. IIRC this algo also implemented in osgShadows. Shadow volumes will have problems with vertical surfaces that cast their own shadow as well as numerical precision issues will mean that some areas will classified in and other areas classified as out of the shadow. The matching of the vertex and fragment shaders handling of ambient light is solution in both cases. Robert. ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] Autoshadow aliasing in shadow maps
Hi, Justo All shadowmapping techniques have problems with such aliasing problems. You can try use shadow volumes technique as it dont suffer from this problem and generates correct shadows in any case, but it have other drawbacks. IIRC this algo also implemented in osgShadows. Cheers, Sergey. 25.08.2011, 22:12, Justo Ureña chil...@hotmail.com: Hi, I´m testing diferent shadows techniques for my scene, and after some adjusts, I got them working fine... Except for very big aliasing that appears in some surfaces that are parallel to the light direction. It happens in all the shadow maps techniques (ShadowMap, StandardShadowMap, LISPSM)... and I´ve tried all the things that I could imagine to get rid of them without success... Please, anyone can help me with that? From my investigation I got that the problem is that the depth map calculated by the shadow camera does not fit exactly with the curved shape in the scene. In the attachment you can see a render of the scene (that only includes the cessna and a vertical directional light that produces the shadow) coloured with the depth map. As you can see, in the laterals of the cessna appear these withe stiches that means that the depth calculated in these texels of the map is infinite, what is obviously wrong. There is any way to avoid this annoying effect? Thank you very much! Cheers, Justo -- Read this topic online here: http://forum.openscenegraph.org/viewtopic.php?p=42241#42241 ___ 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] Autoshadow aliasing in shadow maps
Hi Justo, On Sat, Aug 27, 2011 at 12:17 AM, Justo Ureña chil...@hotmail.com wrote: I´ve tried the ViewDependentShadowMap and although it works great, I still have the same problem with the stiching due to the missing tessels... Good to hear it's work well for you. The aliasing artifact you are still seeing is expected, it's a trait that all shadow technique will have, but if the vertex and fragment shaders are properly setup this issue will disappear, you can still still the artifact with ViewDepententShadowMap as the shaders have been kept deliberately simple. Robert, you´re right about that in a normal illumination, these surfaces should be set to the ambient colour, cause their normals are pendicular with the light direction. But as my scene is an outside static scene, and I don´t want to illuminate a big portion of the scene with the ambient light because it looks flat, I´m trying to implement some kind of hemispheric lighting (from the glsl orange book), but without renouncing to the shadow effect. So, I need this perpendicular surfaces to be lit, and to show the shadows... There is no reason why you can't use different lighting models when doing shadow mapping. The key element to solve the artifact you are seeing is computing the the diffuse+specular element of lighting separate the ambient component and not combining them until you've take the result from the shadow map. Typically the ambient and diffuse+specular components are all combined in the vertex shaders and passed as a single colour to the fragment shader, but instead you'll want to pass these as two colours to the fragment shader and have the fragment shader do the shadow map test, then if you the fragment is the shadow you'll want to just use the ambient contribution, but if it's not in shadow you'll want to add the diffuse+specular component. If this is done correctly then when the normal is perpendicular to the light source the diffuse+specular component will be zero so the end result will be the equal to the ambient component whether you are in the shadow or not. Robert. ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] Autoshadow aliasing in shadow maps
Hi Justo, Take a look to the Variante Shadow Map algorithmhttp://developer.nvidia.com/node/165 to apply shadow on the scene. Instead of use default OpenGL ShadowMap comparaison technique, this algorithm provide a different way to capture and apply shadow. This technique take more resource but with a better result. HTH David Callu 2011/8/25 Robert Osfield robert.osfi...@gmail.com Hi Justo, Surfaces that are parallel to the light source will be subject to numerical aliasing issues that will mean that either the fragment is inside or outside that shadow map. You can't avoid these aliasing issues completely but if the vertex and fragment shaders are set up correctly then the parallel surfaces should in theory have the same ambient lighting regardless of being in the shadow or not so you shouldn't see the aliasing artifact. I have just developed a new shadow technique that you'll find checked into svn/trunk, look for the ViewDependentShadowMap, use the --vdsm option in osgshadow example. All going well this will replace the collection of other shadow techniques. I would recommend testing against this new technique. Robert. On Thu, Aug 25, 2011 at 7:12 PM, Justo Ureña chil...@hotmail.com wrote: Hi, I´m testing diferent shadows techniques for my scene, and after some adjusts, I got them working fine... Except for very big aliasing that appears in some surfaces that are parallel to the light direction. It happens in all the shadow maps techniques (ShadowMap, StandardShadowMap, LISPSM)... and I´ve tried all the things that I could imagine to get rid of them without success... Please, anyone can help me with that? From my investigation I got that the problem is that the depth map calculated by the shadow camera does not fit exactly with the curved shape in the scene. In the attachment you can see a render of the scene (that only includes the cessna and a vertical directional light that produces the shadow) coloured with the depth map. As you can see, in the laterals of the cessna appear these withe stiches that means that the depth calculated in these texels of the map is infinite, what is obviously wrong. There is any way to avoid this annoying effect? Thank you very much! Cheers, Justo -- Read this topic online here: http://forum.openscenegraph.org/viewtopic.php?p=42241#42241 ___ 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 ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] Autoshadow aliasing in shadow maps
Hi, thank you Robert and David for your answers, I really appreciate them. I have just developed a new shadow technique that you'll find checked into svn/trunk, look for the ViewDependentShadowMap, use the --vdsm option in osgshadow example. All going well this will replace the collection of other shadow techniques. I would recommend testing against this new technique. I´ve tried the ViewDependentShadowMap and although it works great, I still have the same problem with the stiching due to the missing tessels... Robert, you´re right about that in a normal illumination, these surfaces should be set to the ambient colour, cause their normals are pendicular with the light direction. But as my scene is an outside static scene, and I don´t want to illuminate a big portion of the scene with the ambient light because it looks flat, I´m trying to implement some kind of hemispheric lighting (from the glsl orange book), but without renouncing to the shadow effect. So, I need this perpendicular surfaces to be lit, and to show the shadows... Take a look to the Variante Shadow Map algorithm to apply shadow on the scene. Instead of use default OpenGL ShadowMap comparaison technique, this algorithm provide a different way to capture and apply shadow. This technique take more resource but with a better result. I´ve already tested another filters as PCF, but the results weren´t so good and it consumed a lot of resources. I´ve read about the VSM algorithm, and I was doubting about implementing it. I think that I´m gonna try it, and I´ll let you know the results. Hopefully it will get rid of the problem. Hopefully! Thank you very much guys! PS: Anyway, I´m still curious with the missing texels problem. I´ve been investigating about it and I couldn´t get anything... Isn´t there any way to make the RTT camera to set the depth of this texel to the fragments one? Do you have any hint about it? Thanks again. Cheers, Justo -- Read this topic online here: http://forum.openscenegraph.org/viewtopic.php?p=42268#42268 ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] Autoshadow aliasing in shadow maps
Hi Justo, PS: Anyway, I´m still curious with the missing texels problem. I´ve been investigating about it and I couldn´t get anything... Isn´t there any way to make the RTT camera to set the depth of this texel to the fragments one? Do you have any hint about it? There aren't any missing texels as you seem to think. In shadow map space, that area simply maps nowhere (it falls between 2 texels). You have 2 options: higher shadow map resolution so that the area where this happens is smaller, or do some filtering to hide the effect. We had a similar effect where we would get a kind of moiré pattern over surfaces. It was most visible on very white surfaces and when the shadow map was stretched over a large area. Zoomed up close, the appearance was identical to what you have. In our case simple PCF filtering worked for us, but you say you've tried it and rejected it. You could try some other type of filtering, or increase your shadow map resolution, though I doubt you'll get to a point where the artifact is not visible while keeping a reasonable resolution... For us it was still visible at 4096^2 resolution, so filtering was the best we could do. Unfortunately this is the kind of thing (like z-buffer precision leading to z-fighting) where you just have to know what the artifacts could be, and manage all your options so you minimize the appearance of the artifacts. There is no perfect solution. Hope this helps, J-S -- __ Jean-Sebastien Guayjean-sebastien.g...@cm-labs.com http://www.cm-labs.com/ http://whitestar02.dyndns-web.com/ ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] Autoshadow aliasing in shadow maps
Hi Justo, Surfaces that are parallel to the light source will be subject to numerical aliasing issues that will mean that either the fragment is inside or outside that shadow map. You can't avoid these aliasing issues completely but if the vertex and fragment shaders are set up correctly then the parallel surfaces should in theory have the same ambient lighting regardless of being in the shadow or not so you shouldn't see the aliasing artifact. I have just developed a new shadow technique that you'll find checked into svn/trunk, look for the ViewDependentShadowMap, use the --vdsm option in osgshadow example. All going well this will replace the collection of other shadow techniques. I would recommend testing against this new technique. Robert. On Thu, Aug 25, 2011 at 7:12 PM, Justo Ureña chil...@hotmail.com wrote: Hi, I´m testing diferent shadows techniques for my scene, and after some adjusts, I got them working fine... Except for very big aliasing that appears in some surfaces that are parallel to the light direction. It happens in all the shadow maps techniques (ShadowMap, StandardShadowMap, LISPSM)... and I´ve tried all the things that I could imagine to get rid of them without success... Please, anyone can help me with that? From my investigation I got that the problem is that the depth map calculated by the shadow camera does not fit exactly with the curved shape in the scene. In the attachment you can see a render of the scene (that only includes the cessna and a vertical directional light that produces the shadow) coloured with the depth map. As you can see, in the laterals of the cessna appear these withe stiches that means that the depth calculated in these texels of the map is infinite, what is obviously wrong. There is any way to avoid this annoying effect? Thank you very much! Cheers, Justo -- Read this topic online here: http://forum.openscenegraph.org/viewtopic.php?p=42241#42241 ___ 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
