gdalgorithms-list

[Algorithms] Stopping shadow volumes from going through geometry

[Fong, J. <JF...@Bl...>]

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
 

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

[Gilles M. <gil...@fr...>]

MessageHi,

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

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

[Joris M. <jor...@pa...>]

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 
of the shadow volume nearer from the character.
If it's a sun-like light, radiosity of the environment should make look
that 
correct to your eyes.
 
Gilles.
 
----- Original Message ----- 

From: Fong, Jay <mailto:JF...@Bl...>  
To: 'gda...@li...' 
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
 

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

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

MessageYou 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

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

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

[Joris M. <jor...@pa...>]

this is what i mean, in "real-life" this is not possible. Usually the
static geom uses some prebaked form of shadowing (lightmap, vertex
darkening, whatever) and it will clash with the dynamic shadowcaster. We
only want the character to cast shadows on the vicinity using stencil
and leave the rest as-is. Ofcourse when your initials are JC and you are
making a game called D III things change a bit ;)
 
 
Joris

-----Original Message-----
From: gda...@li...
[mailto:gda...@li...] On Behalf Of John
Pollard
Sent: Friday, November 22, 2002 1:31 AM
To: gda...@li...
Subject: Re: [Algorithms] Stopping shadow volumes from going through
geometry


Hit 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 ----- 
From: John  <mailto:jo...@3d...> Pollard 
To: gda...@li... 
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 ----- 
From: Joris  <mailto:jor...@pa...> Mans 
To: gda...@li... 
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 
of the shadow volume nearer from the character.
If it's a sun-like light, radiosity of the environment should make look
that 
correct to your eyes.
 
Gilles.
 
----- Original Message ----- 

From: Fong,  <mailto:JF...@Bl...> Jay 
To: 'gda...@li...' 
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
 

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

[John P. <daw...@at...>]

MessageHmm, if you must do darkening stencil shadows, and you don't want =
them to go through walls, maybe you could do a four-pass scheme, where =
you render two types of shadow volumes.=20

First, clear stencil to 128 or something.  Then render the shadowvolumes =
to the stencil buffer.   At this point, the stencil buffer will contain =
values where you should darken the screen.  Draw a full screen invisible =
quad that sets this shadow region to a certain value other than 128, say =
129.  At this point, you have values of 128, and 129 in the stencil =
buffer.  129 is currently where the screen should be shadowed.  Now, for =
all the polygons that you want the shadow volume to be blocked by, =
extrude those (call them anti-shadowvolumes) and render the =
anti-shadowvolumes into the stencil buffer.  They will invalidate the =
parts of the screen that are blocked by the anti-shadowvolumes.  =
Finally, draw another fullscreen quad, and darken areas that remain 129 =
in the stencil buffer.

Would this work?  Sounds like alot of passes, but it would allow you to =
keep an old school renderpipe, and use the darken stencil shadow volume =
method, and still allow geometry to block the shadows.  Your probably =
going to still see funny anomalies though, if your not careful about =
choosing the anti-shadowvolumes.  You'd want to make sure that the =
blocking object in question truly blocked the entire shadow, or the =
shadow will have "holes" in it.

-John
  ----- Original Message -----=20
  From: Joris Mans=20
  To: gda...@li...=20
  Sent: Thursday, November 21, 2002 7:11 PM
  Subject: RE: [Algorithms] Stopping shadow volumes from going through =
geometry


  this is what i mean, in "real-life" this is not possible. Usually the =
static geom uses some prebaked form of shadowing (lightmap, vertex =
darkening, whatever) and it will clash with the dynamic shadowcaster. We =
only want the character to cast shadows on the vicinity using stencil =
and leave the rest as-is. Ofcourse when your initials are JC and you are =
making a game called D III things change a bit ;)


  Joris
    -----Original Message-----
    From: gda...@li... =
[mailto:gda...@li...] On Behalf Of John =
Pollard
    Sent: Friday, November 22, 2002 1:31 AM
    To: gda...@li...
    Subject: Re: [Algorithms] Stopping shadow volumes from going through =
geometry


    Hit 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