[gameprogrammer] Re: culled objects and shadow volumes
- From: Alan Wolfe <alan.wolfe@xxxxxxxxx>
- To: gameprogrammer@xxxxxxxxxxxxx
- Date: Tue, 28 Apr 2009 08:42:11 -0700
That is some pretty good advice, thanks Sami.
I found this late last night and this technique talks about expanding the
view frustum and then doing regular object culling so you don't have to
create the shadow volumes or test which direction the shadows will be cast.
http://www.gamedev.net/columns/hardcore/shadowcast/
I'm going to have to look at the pros and cons of your method vs this method
and see which makes more sense for my game cause I was thinking this article
was the best way, but now im not so sure (:
Thanks!
On Tue, Apr 28, 2009 at 5:44 AM, Sami Näätänen <sn.ml@xxxxxxxxxxxxxxx>wrote:
> On Tuesday 28 April 2009 09:10:44 Alan Wolfe wrote:
> > Heya!
> >
> > I'm culling objects against the viewing frustum and am only rendering the
> > shadows of non culled objects, so am hitting the problem where objects
> that
> > are outside of the frustum that should be casting shadows into the
> frustum
> > aren't.
> >
> > An easy solution might be to check if the shadow volumes intersect with
> the
> > frustum but the problem with that is that all objects would have to be
> > considered since i have dynamic lighting and would possibly need to
> > re-compute the shadow volumes every frame, which really hampers the
> > gainstof culling against the frustum in the first place (at least for the
> > shadow rendering).
> >
> > Does anyone know any good ways to deal with this situation?
>
> Some ideas:
>
> First do like you now do and if the object would be culled do the testing
> for
> the lighting. Ie if there are any light sources that could cast a shadow
> with
> the tested object to the direction of the view frustum. If there are such
> light sources, create the shadow volume for those light sources only and
> test
> the shadow volumes against the frustum. You don't need to create all the
> shadow volumes as you obviously need only those that really are able to
> cast
> shadow to the direction of the frustum.
>
> an example:
> L is one light source
> O is the tested object
> c is the camera
> f is area that is inside the view frustum.
>
> ---------------------------------------
> L
>
> O
> c
> fffffffffffffffffff
> fffffffffffff
> ffffff
> ---------------------------------------
>
> so if the vector from L through O will intersect with the view frustum you
> need to create the shadow volume.
>
> You also want to consider the size of the shadow volume:
> so calculate the minimum distance of the line from L through O to the
> frustum.
> Also the distance from that point to L is needed.
> Also the radius of the bounding sphere of object O and the length from O to
> L
> is needed.
>
> LO = length from the light to the center of the object.
> Ld = length from the light to the point of minimum distance to the frustum
> r = radius of the objects bounding sphere
> d = minimum distance from the frustum of the line that goes from L through
> the
> center of the object O.
>
> So if the following comparison is true the shadow volume of the objects
> bounding sphere intersects with the frustum. So there are a chance that the
> real shadow volume will do that as well, so it should be tested/used. You
> might want to test, which of these is more efficient. Simply using the
> final
> shadow volume if the shadow volume of the objects bounding sphere
> intersects
> or further testing will stress different parts of the system.
>
> r/LO > d/Ld
>
>
> You of course want to do all this testing in 3D and not in 2D like the
> ASCII
> example.
>
>
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