Re: [osg-users] inverse shadows

2009-02-13 Thread Art Tevs 
Hi Ben,

it is a usual behaviour of shadow map algorithms. The problem is in the 
projection computation, which is done, when projecting the shadow map texture 
into the scene. I do not exactly know, how OSG handles this issue, but here you 
can find more general information on this:[url]
http://www.gamedev.net/community/forums/topic.asp?topic_id=485577[/url]

cheers,
art

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http://osgforum.tevs.eu/viewtopic.php?p=6780#6780





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Re: [osg-users] inverse shadows

2009-02-13 Thread Wojciech Lewandowski 
Ben,

Looks like back projection issue. If your light is spot light with cone  180 
deg then it could be fixed by one of the tricks used to clip back projected 
textures (additional clip plane or special 1D texture). You should find a lot 
of stuff in the web that explain texgen projections and related issues.
 
But if your light is omnidirectional I am afraid none of the shadow mapping 
algorithms in osgShadow will work. They may do if omnidirectional light could 
be approximated by spot light for this particular view/frame. 

But in general case omnidirectional light requires more than one shadow map. 
And your picture  looks like such situation where one shadow map does not 
suffice.  

Cheers,
Wojtek



  - Original Message - 
  From: Ben Axelrod 
  To: osg-users@lists.openscenegraph.org 
  Sent: Friday, February 13, 2009 5:08 PM
  Subject: Re: [osg-users] inverse shadows


  *ping*

   

  Sorry for the repost, but there has not been a response on this in several 
days.

   

  I am seeing some strange behavior with the ShadowMap.  The attached images 
show a white sphere which is at the same location as the only light in the 
scene.  It is between an arrow, and a cube.  The shadow on the arrow gets 
back-cast to the cube, and even shows up on the back of the cube.  

   

  Is this normal?  How can this behavior be fixed?  I am using OSG version 2.6.

   

  Thanks,

  -Ben



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