Hi Wojtek, thanks a lot for your detailed answer. I will work through the example within one of the next holydays, as I am not a professional programmer (I´m a math teacher) and will need some quiet time for a demanding task like this. My software is a math-software to illustrate vector geometry, and thus displays planes and so on simply as polygons. That´s the reason I need two-sided materials (or at least I decided to do so, the alternative would have been to use more massive planes). For the time being it is a comfort for me that I didn´t make a simple mistake and that it is quite some work to adjust the StandardShadowMap to two-sided polygons.
Who maintains ShadowMap? I´d like the maintainer to do some tests with my shader. If you think it´s better than the standard one, I´ll refactor it into the Shadow-Map code. For a first impression, see the images in the last mail. Regards & thanks for the example, Andreas Wojciech Lewandowski schrieb: > Hi Andreas, > > If you want to use dual sided materials I believe you will have to > review > and probably modify the shaders in StandardShadowMap.cpp. I am certain > Vertex shader computes ligthing using front lighting and assigns the same > colors to backfacing polygons. > Another issue would be usage of back faces for shadow map rendering. I > guess if you want to use dual face materials you will need to > override this. > So many people have so many varying requests for shadows that my > recomendation for them would be to create their own ShadowTechnique > class based on one of LispSM or MinimalShadowMap or even > StandardShadowMap. But comparing results, this last one does not > really differ that much from ShadowMap which is much easier to override. > When overriding any of above classes its important to override inner > ViewData class which provides View related resources storage and > management. By overriding ViewData::init method you get access to all > statesets used by base classes and you can easily override all state > attributes. > I have prepared an example class (MyViewDependentShadowMap) which > shows how to override any of classes stemming from > ViewDepenedentShadowTechnique. This class illustrate how to add soft > shadows to MinimalDrawBoundsShadowMap class (should be appropriate for > you). Have a look at it and modify to your needs. > > HTH, > Wojtek Lewandowski > > -------------------------------------------------- > From: "Andreas Goebel" <[email protected]> > Sent: Saturday, November 21, 2009 1:57 PM > To: "OpenSceneGraph Users" <[email protected]> > Subject: Re: [osg-users] Shadows on two-sided polygons > >> Hi Jean-Sébastien, >> >>>> I have turned off those things, and now it works good for me. Should I >>>> refactor that in a way that the application programmer can choose the >>>> behaviour and submit that? >>> >>> You could, but I think setting those things via overridden state is >>> also acceptable, since if you need that you'll probably know what to >>> set... >>> >> You mean by setting the StateAttribute CullFaces to off and override for >> my shadowed scene? This would probably work (even though it is set with >> override in the ShadowMap? Which will override which?), but not for the >> polygon-offset, as this is not controlled with state. I mean this line: >> >> // negative polygonoffset - move the backface nearer to the eye point so >> that backfaces >> // shadow themselves >> float factor = _polyOffset[0]; >> float units = _polyOffset[1]; >> >>>> Another thing: I have written a vertex and a fragment shader that work >>>> together in a way that allows the shadows to be rendered exactly in >>>> the >>>> ambient color. This means that shadowed surfaces look the same as >>>> surfaces that face away from the light. This gives a much more natural >>>> feeling, and you don´t get false shadows on the backs of polygons. I >>>> needed the vertex shader to get the correct ambient color, I think >>>> it is >>>> not possible to do this with a fragment shader alone. >>> >>> I assume you're talking about osgShadow::ShadowMap? The shaders used >>> for the ViewDependentShadow classes (LightSpacePerspectiveShadowMapDB, >>> CB, VB) already do this. Note that osgShadow::StandardShadowMap is the >>> equivalent of osgShadow::ShadowMap but under the ViewDependentShadow >>> architecture, so you could have used that and you would have gotten >>> the right shadow ambient color. >>> >> It´s great to hear that, I haven´t used the new classes yet, as they are >> not (at least in 2.8.2) part of the shadow-Example and I could not >> easily play with them. However, I have made an option in my program to >> use the StandardShadowMap, and it does not work for me (yet). Here are >> the problems: >> >> - the side facing away from a light is not dark, example: >> http://raumgeometrie.de/NeueBilder/testbilder/IncorrectBack.png >> >> - the backside of a shadowed plane shows the shadow, too: >> >> http://raumgeometrie.de/NeueBilder/testbilder/IncorrectShadowOnBack.png >> >> The correct images (with my shaders) look like this: >> >> http://raumgeometrie.de/NeueBilder/testbilder/CorrectBack.png >> >> And this: >> >> http://raumgeometrie.de/NeueBilder/testbilder/NoShadowOnBackOfPlane.png >> >> Is it possible to render a more correct shadow for models like mine with >> StandardShadowMap? It seems a promising technology to me, I would like >> to use it, and the results (where they are correct) look really good. >> >> Regards, >> >> Andreas >>> You can always submit those shaders (as part of modified ShadowMap.cpp >>> files so that they work by default), I'm sure anyone still using >>> osgShadow::ShadowMap will be glad you do. >> I think it´s nicer to have the shaders as separate files, one can easily >> load them and use them, no need to modify the source. >>> >>> J-S >> >> _______________________________________________ >> 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
