HI Rui,

Thanks for the links to the data, I will download and have a
experiment later, most likely tomorrow as I have to go out quite soon.

The screenshot is suggests to me that the main artefact is simply that
the shader used/fixed function pipeline isn't computing the shadowed
colour correctly and would disappear if appropriate shaders were used
to make sure the back facing triangles are coloured the same as the
shadowed region.  When using the standard fixed function pipeline you
just get black for the shadowed around so the result always has this
artefact.

Robert.

On 12 March 2012 13:20, Wang Rui <wangra...@gmail.com> wrote:
> Hi Robert,
>
> I'd like to provide a set of city models for shadow tests. It is already
> constructed with paged LODs so can be viewed smoothly on my Windows 7 and
> GTX 460. I've uploaded it at box.com, totally two compressed packages:
> http://www.box.com/s/s1bnf4eqenrc30opxzj4
> http://www.box.com/s/ubu4186593fjc8tslntq
>
> Of course tarballs are not suitable for public test. It should be
> comfortable if we could load and render the city from an HTTP address, just
> like the earth_bayarea example dataset. The snapshot attached shows that
> most of the shadows are at the right place but some with obvious aliasing
> issues and streaks (as on the right bottom side).
>
> Cheers,
>
> Wang Rui
>
>
> 2012/3/12 Robert Osfield <robert.osfi...@gmail.com>
>>
>> Hi Rui,
>>
>> Artifacts can be caused by a number of different reasons, as I have
>> seen the models, screenshots of the artefacts I don't feel comfortable
>> pointing at any particular cause or solution.
>>
>> Having a public model we can test against would be very useful.  Also
>> modifying the osgshadow example to have a unit test for these case
>> would also be useful.  Given a unit test we as group can start
>> refining things for the problem cases.
>>
>> As a more general note ViewDependentShadowMap doesn't yet provide
>> shaders that resolve the issue correct lighting of shadows, the thread
>> you link to discusses this topic.  Introducing the required shaders as
>> an option into  ViewDependentShadowMap would address one of the areas
>> that artefacts can be seen when users don't provide their own shaders
>> that do the lighting correctly.  This won't solve all the potential
>> artefacts that we see when doing shadow mapping but it would at least
>> discount one possible set of problems.
>>
>> Robert.
>>
>> On 12 March 2012 09:38, Wang Rui <wangra...@gmail.com> wrote:
>> > Hi all,
>> >
>> > I'm currently working on an example that uses
>> > osgShadow::ViewDependentShadowMap for generating dynamic shadows on a
>> > large
>> > area of buildings. It can work correctly on a huge city which is created
>> > by
>> > CityEngine and then converted to OSG styled scene graph. It also
>> > generates
>> > aliasing issues as expected, but I'm still looking for some good
>> > solutions
>> > to reduce such problem and want to discuss them in this thread if
>> > possible.
>> > My test program and a simple shader file can be found in attachement.
>> >
>> > I've already read a similar topic at:
>> >
>> > http://lists.openscenegraph.org/htdig.cgi/osg-users-openscenegraph.org/2011-August/053731.html
>> > And I believe it is necessary to apply some filters on the shadow map
>> > (the
>> > test shader file simply uses PCF here) and increase the texture
>> > resolution
>> > as well. But for huge scene, a 4096-sized RTT texture will be a heavy
>> > burden. So I wonder if there are some more methods to choose, for
>> > example,
>> > is it possible to change the internal format of the texture to
>> > GL_DEPTH_COMPONENT32 to improve the shadow comparision process?
>> >
>> > Meanwhile, is it necessary to perform a screen space blurring to reduce
>> > the
>> > aliasing effect? It is a serious problem for my scene now as I can't use
>> > a
>> > very high resolution. Could anyone suggest some other possible methods
>> > on
>> > the post-processing level? To be honest, the ViewDependentShadowMap is
>> > the
>> > best shadow solution for me at present as it is easy to be integrated
>> > with
>> > custom shaders and embedded into a deferred shading framework.
>> >
>> > The test city models are about 180MB. If any of you think it important
>> > for
>> > digging into the problem. I'd like to share them freely, too, as I
>> > believe
>> > these automatically generated models should not have any copyrights with
>> > them. :-)
>> >
>> > Cheers,
>> >
>> > Wang Rui
>> >
>> >
>> > _______________________________________________
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>> > osg-users@lists.openscenegraph.org
>> >
>> > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
>> >
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