Re: [Algorithms] Stopping shadow volumes from going through geometry

[John P. <jo...@3d...>]

MessageHit reply too fast :-O

>>You don't even need to make the entire scene cast shadows
Actually, the character's shadow will still go through the wall.  But =
you can simply make the wall cast shadows as well.  Since it's blocking =
imcoming light, it works.  And no double darkening.

  ----- Original Message -----=20
  From: John Pollard=20
  To: gda...@li...=20
  Sent: Thursday, November 21, 2002 6:23 PM
  Subject: Re: [Algorithms] Stopping shadow volumes from going through =
geometry


  You won't get the double darkening if you do all your shadowvolumes at =
once at the end, and do the fullscreen quad to darken, but it still =
doesn't solve the problem completely, as the ledge will now go through =
walls, and it's a never ending process, unless like you said, the whole =
scene cast shadows.  But this method is such a pain, and you never =
really fix all the problems.

  Our shadowvolumes actually block imcoming light, so the problem goes =
away (which is how most people are doing it these days I'm assuming).  =
The drawback, is you have to interleve your light rendering code between =
the shadowvolume rendering.  The advantage, is all those problems go =
away.  You don't even need to make the entire scene cast shadows.  =
Everything just works.

    ----- Original Message -----=20
    From: Joris Mans=20
    To: gda...@li...=20
    Sent: Thursday, November 21, 2002 6:04 PM
    Subject: RE: [Algorithms] Stopping shadow volumes from going through =
geometry


    this is the answer i see all the time when ppl ask this question =
(please dont take this personally), but as we all know this doesnt solve =
it, even with the ledge casting a shadow you will get "double shadowing" =
under the ledge.
    So if anyone has a way of solving this which does not require =
stencil-shadowing the entire scene ;) please reply as i dont know it =
either :|


    Joris
      -----Original Message-----
      From: gda...@li... =
[mailto:gda...@li...] On Behalf Of =
Gilles Marion
      Sent: Thursday, November 21, 2002 10:17 PM
      To: gda...@li...
      Subject: Re: [Algorithms] Stopping shadow volumes from going =
through geometry


      Hi,

      I think the ledge should also cast its shadow onto the ground, no =
?
      If so, it doesn't matter if the shadow volume is extruded past the =
ledge.
      If fillrate is your bottleneck, think about clipping (cpu =
intensive), or try setting the far side=20
      of the shadow volume nearer from the character.
      If it's a sun-like light, radiosity of the environment should make =
look that=20
      correct to your eyes.

      Gilles.

      ----- Original Message -----=20
        From: Fong, Jay=20
        To: 'gda...@li...'=20
        Sent: Thursday, November 21, 2002 9:29 PM
        Subject: [Algorithms] Stopping shadow volumes from going through =
geometry


        Hello,

        I was wondering if there is some way to prevent shadows, =
generated by the stencil shadow volume technique, from being extruded =
through other objects in the scene?  e.g. a character standing on an =
overhanging ledge above ground casts a shadow on the ledge but also onto =
the ground below the ledge.

        I thought about clipping the extruded shadow polys against the =
world geometry but I'm hoping for a more elegant (i.e. simpler) solution =
since our world geometry is quite dense.

        Any solutions or links/pointers to papers related to this issue =
would be much appreciated!

        Thanks,
        Jay