Any Alpha Culling in WPF/3D ?

I want to draw multiple objects, in a 3D Viewport, with textures possibly
having an alpha channel on them. The material itself is not transparent, its
opacity is 1.0.

What I see for the moment is a strange behavior, the "transparent" part of
some objects hides the rest of the scene. This seems to comes from the
zBuffer conflicting with the transparency.
As far as I understood there is no way to disable zWriting in WPF (except
using Emissive Material, but I don't want to blend the whole objects, I just
need some transparency on textures.)
So my question is , is there some sort of alpha culling in WPF. Avoiding the
contribution of a pixel, under a certain alpha threshold, in the colorBuffer
AND the zBuffer?

WPF 3D doesn't z order the objects. When dealing with transparency on
materials, the author must handle the z-order.

I have a sample in my sample pack at http://www.therhogue.com/WinFX - the
collageview sample.

As one poster commented, this is a lot of heavy lifting, and I agree. When
dealing with circular transparency, the app must be architected correctly to
allow for proper arrangement of geometries with transparent
material...without proper architecture the devloper will hit a dead end.

I can only hope zbuffer sorting is a feature for WPF version 2.0 as it may
be easier for the WPF team to create a flat tree for ordering rather than
have everyone else have to invent this framework wheel.


"Lois Lacroux" wrote:

> I want to draw multiple objects, in a 3D Viewport, with textures possibly
> having an alpha channel on them. The material itself is not transparent, its
> opacity is 1.0.
>
> What I see for the moment is a strange behavior, the "transparent" part of
> some objects hides the rest of the scene. This seems to comes from the
> zBuffer conflicting with the transparency.
> As far as I understood there is no way to disable zWriting in WPF (except
> using Emissive Material, but I don't want to blend the whole objects, I just
> need some transparency on textures.)
> So my question is , is there some sort of alpha culling in WPF. Avoiding the
> contribution of a pixel, under a certain alpha threshold, in the colorBuffer
> AND the zBuffer?
>

Not that this helps you, but SpecularMaterial doesn't write to Z either.

Jordan

>I want to draw multiple objects, in a 3D Viewport, with textures possibly
> having an alpha channel on them. The material itself is not transparent,
> its
> opacity is 1.0.
>
> What I see for the moment is a strange behavior, the "transparent" part of
> some objects hides the rest of the scene. This seems to comes from the
> zBuffer conflicting with the transparency.
> As far as I understood there is no way to disable zWriting in WPF (except
> using Emissive Material, but I don't want to blend the whole objects, I
> just
> need some transparency on textures.)
> So my question is , is there some sort of alpha culling in WPF. Avoiding
> the
> contribution of a pixel, under a certain alpha threshold, in the
> colorBuffer
> AND the zBuffer?
>

Thanks for the answer,

It's too bad that zWriting cannot be disabled, at least I could have perform
a non-orderer drawing pass only for "transparent" objects.

It's strongly limiting the capacity of WPF/3D regarding transparent objects,
and I'm sure that there is plenty of 3D scene or UIs where transparency is
involved.
And I'm not speaking of intersecting transparent objects.

Lois

"TheRHogue" wrote:

> WPF 3D doesn't z order the objects. When dealing with transparency on
> materials, the author must handle the z-order.
>
> I have a sample in my sample pack at http://www.therhogue.com/WinFX - the
> collageview sample.
>
> As one poster commented, this is a lot of heavy lifting, and I agree. When
> dealing with circular transparency, the app must be architected correctly to
> allow for proper arrangement of geometries with transparent
> material...without proper architecture the devloper will hit a dead end.
>
> I can only hope zbuffer sorting is a feature for WPF version 2.0 as it may
> be easier for the WPF team to create a flat tree for ordering rather than
> have everyone else have to invent this framework wheel.
>
>
> "Lois Lacroux" wrote:
>
> > I want to draw multiple objects, in a 3D Viewport, with textures possibly
> > having an alpha channel on them. The material itself is not transparent, its
> > opacity is 1.0.
> >
> > What I see for the moment is a strange behavior, the "transparent" part of
> > some objects hides the rest of the scene. This seems to comes from the
> > zBuffer conflicting with the transparency.
> > As far as I understood there is no way to disable zWriting in WPF (except
> > using Emissive Material, but I don't want to blend the whole objects, I just
> > need some transparency on textures.)
> > So my question is , is there some sort of alpha culling in WPF. Avoiding the
> > contribution of a pixel, under a certain alpha threshold, in the colorBuffer
> > AND the zBuffer?
> >

The trick here, if you can get away with it, is to use an emssive
material with alpha - the operation is strictly additive, and so
order-independant.

Works best for me against dark backgrounds.

As for intersecting objects - its not just about intersection, but you
can also set up non-intersecting polygons A,B,C so that A overlaps B
which overlaps C which overlaps A. Theonly way to resolve that is to
split one of the polygons.