Google for Shadow Maps. You will come up with a number of techniques. Few of them:
http://www.punkuser.net/vsm/ http://gamma.cs.unc.edu/LOGPSM/ http://developer.download.nvidia.com/presentations/2008/GDC/GDC08_SoftShadowMapping.pdf Most of these belong to the family of soft shadow algorithms. Soft shadows usually oversample depth texel and produce some average shadow term. Clamping this term to 0 if value is below certain threshold (for example <0.25) usually removes some of self shadowing artifacts. I will have the second look on the code but not today. Wojtek From: Trajce Nikolov Sent: Friday, January 15, 2010 10:16 PM To: OpenSceneGraph Users Subject: Re: [osg-users] light lobes and shadow maps do you have some pointers, papers to the work of this guys? I am interested in learning what is that about Nick http://www.linkedin.com/in/tnick Sent from Ünalan, İstanbul, Turkey On Fri, Jan 15, 2010 at 11:01 PM, Wojciech Lewandowski <[email protected]> wrote: Nick, I may look into the code but don't expect much this time. You need to attach the code first, though ;-). Few academy guys wrote couple dissertations on rasterization and aliasing errors in shadow mapping. Unless you try to do some exotic stuff like variance or logarithmic map you will have to use polygon offset. I guess you will end up to cranking up PolygonOfset even more if current values fail at some distance. I don't really have other tricks in my sleeve. Wojtek From: Trajce Nikolov Sent: Friday, January 15, 2010 9:08 PM To: OpenSceneGraph Users Subject: Re: [osg-users] light lobes and shadow maps That is exactly what I did. Please have a look at the updated code. The uniform is updated thru a callback and it multiplies the matrices, still there is a visual artifact.I dont have compute_near_far. The projection matrix is fixed with very small far plane (100 units, with the znear of 0.01). Nick http://www.linkedin.com/in/tnick On Fri, Jan 15, 2010 at 9:47 PM, Wojciech Lewandowski <[email protected]> wrote: Hi, Light close to obstacles ? If you have COMPUTE_NEAR_FAR it may clamp near plane to very small value which may impact depth resolution. Other issue maybe related to GLSL float precision. The trick with multiplying view space coord by inverse view matrix to get world coord is performed on float values inside GLSL. Precision wise it would be better to multiply light camera MVP matrix by main camera INVERSE VIEW on the CPU. Osg Matrices use doubles. Put the result of the multiplication on GLSL matrix Uniform and use it to multiply gl_Vertex in the shader. Such approach multiplies matrices with high precision and resulting matrix will be better suited to be cast on single prec. GLSL matrix. The drawback of this solution is: you need to update the uniform every frame, because main camera view changes with each move. Wojtek From: Trajce Nikolov Sent: Friday, January 15, 2010 7:37 PM To: OpenSceneGraph Users Subject: Re: [osg-users] light lobes and shadow maps Hi Wojtek, now I spent more time exploring this, the polyoffset seam to work, but there is still a bit of shimmering. Its interesting, I put the light source in move, when it moves backwards, the obstacles are lighten ok, but forward, when the light comes close to the obstacles, the lighting is incorrect with shimmering . Any clue how to resolve this artifact ? Nick http://www.linkedin.com/in/tnick On Fri, Jan 15, 2010 at 4:48 PM, Trajce Nikolov <[email protected]> wrote: ok .. make sense. Here is updated code, if some one wants to benefit from. LightLobes with handling of obstacles :). Thanks to Wojiech, Robert and the online community Nick http://www.linkedin.com/in/tnick Sent from Devlet, Ankara, Turkey On Fri, Jan 15, 2010 at 3:53 PM, Wojciech Lewandowski <[email protected]> wrote: 0.0 <= shadow2DProj( shadow_texture, projShadow ).r <= 1.0 Shimering is a result of self shadowing. Boosting depths in shadow map with glPolygonOffset usuallly fixes this. There are many schools for PolygonOffset settings. I usually set glPolygonOffset( 1.1, 4.0 ) and draw objects with front face culling (see StandardShadowMap::ViewData::init(0 for details ). But for this setup models need to work correctly with backface culling on. If you do not enforce backface culling PolygonOffset may need different initialization. Wojtek ----- Original Message ----- From: Trajce Nikolov To: OpenSceneGraph Users Sent: Friday, January 15, 2010 2:46 PM Subject: Re: [osg-users] light lobes and shadow maps one more question. What are the possible values for shadow2DProj( shadow_texture, projShadow ).r ? I am trying to put the light attenuation back ..... and to avoid the shimmering Nick http://www.linkedin.com/in/tnick Sent from Devlet, Ankara, Turkey On Fri, Jan 15, 2010 at 3:35 PM, Trajce Nikolov <[email protected]> wrote: Hey Wojtek !!!! Thanks a lot. !! I will tune it to fix the shimmering Nick http://www.linkedin.com/in/tnick On Fri, Jan 15, 2010 at 3:08 PM, Wojciech Lewandowski <[email protected]> wrote: Trajce, Attached is a fixed source code. There is a lots of shadow shimmering on my GF8800. You will have to add some depth bias while rendering shadow map. Selection proper PolygonOffset values is usually a matter of trial and error so leave this for you. Wojtek ----- Original Message ----- From: Trajce Nikolov To: OpenSceneGraph Users Sent: Friday, January 15, 2010 9:58 AM Subject: Re: [osg-users] light lobes and shadow maps ABout the code. I use shader to simulate lght lobes thru phong lighting in the shader. Then I use shadow maps to detect the area behind the obstacles that need not to be lighten. Most is mixture of shadow maps technique with lighting scheme. Code snippets borrowed from all around Nick http://www.linkedin.com/in/tnick Sent from Devlet, Ankara, Turkey On Fri, Jan 15, 2010 at 10:54 AM, Trajce Nikolov <[email protected]> wrote: Hi Guys, here is the code. Nick http://www.linkedin.com/in/tnick Sent from Devlet, Ankara, Turkey On Thu, Jan 14, 2010 at 11:42 PM, Wojciech Lewandowski <[email protected]> wrote: Hi Nick, Post the troublesome code and elaborate a bit more about the problem. If its really a minute or two I am sure someone will be able to help. Wojtek Lewandowski From: Trajce Nikolov Sent: Thursday, January 14, 2010 8:58 PM To: OpenSceneGraph Users Subject: [osg-users] light lobes and shadow maps Hi community, I have some shader that does some lighting in the scene. Now studying osgShadow and the techniques. I want to a shadow map technique to disable the lightening of the scene behind obstacles. I have some code done, but not working. I need some help, someone experienced with GLSL to spend a minute or to to have a look and if possible to spot the problem. Anyone? Thanks a lot Nick http://www.linkedin.com/in/tnick Sent from Izmit, 41, Turkey ------------------------------------------------------------ _______________________________________________ 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 ---------------------------------------------------------------- _______________________________________________ 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 ---------------------------------------------------------------------- _______________________________________________ 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 ---------------------------------------------------------------------------- _______________________________________________ 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 ------------------------------------------------------------------------------ _______________________________________________ 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 -------------------------------------------------------------------------------- _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
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