Hi David,
In the case where the objects that are casting shadows have expensive
fragment shaders, I would prefer to turn these shaders off so that we
just get a quick depth only pass. Fortunately my expensive shaders sit
above the object's scenegraph, and so I can envisage an approach in
which my unshaded object has two parent nodes (say A and B), which are
both children of the shadow node. A would have the castsShadow mask and
a cheap shader, and B would have the receivesShadow mask and the
expensive shader.
Does this sound like an acceptable approach?
If you're using the ViewDependentShadow techniques, they already disable
shaders while rendering the shadow pass. (note that they also disable
blending, which is a problem if you have objects which are solid but
whose textures give holes, like a chain link fence for example - the
object's shadow will look completely solid instead of showing the holes
as it should)
I don't remember if the osgShadow::ShadowMap does the same, but it
should. It makes sense to disable as much as possible for the shadow
pass since all you want is depth information.
If you find that your shaders are still being called, then yes, what you
suggest above is reasonable.
For good architectural reasons, I can not place one of my desired shadow
receiving items underneath the shadow node. Hence I would like access to
the shadow texture, so that it can bind it explicitly. Would allowing
the ShadowTechnique classes to expose their RTT shadow texture so that
something else can also bind it be a problem in general? At the moment
its protected. Is this something worth submitting or should I just
subclass/rewrite?
I would subclass and just add a public getter for the texture since it's
protected. Pretty simple. I wonder what the "good architectural reasons"
are, but let's not get into that discussion :-)
I realise that multitextured items aren't really supported by the
out-of-the-box shadow techniques, but at the moment the handling of the
shadow texture units and "base" texture units seems a little clumsy, and
difficult to extend. Does anybody else have any experience of using
shadows with objects that are already multitextured (e.g. diffuse and
normal mapped)? It looks to me that if you have any other shaders
knocking around your scenegraph, you need to subclass ShadowTechnique to
support your usage model. Is that what people have done in the past?
I don't really see why you can't just change the shaders, making sure
your new shaders use the same uniform and sampler names and do the right
calculations for shadows, while doing multitexturing.
For osgShadow::ShadowMap, as long as the base texture is in unit 0 and
the shadow map in unit 1, you're OK, so you can use units 2, 3, 4... for
other textures. In the case of the ViewDependentShadow techniques, you
can change the texture units used by the base texture and shadow
texture, which does a search-and-replace in the shader code, so you
could use units 0, 1, 2 as textures and 3 as shadow map as long as you
set it that way in the ShadowTechnique.
Hope this helps,
J-S
--
______________________________________________________
Jean-Sebastien Guay [EMAIL PROTECTED]
http://www.cm-labs.com/
http://whitestar02.webhop.org/
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