From: Dave Akers (dla@engr.sgi.com)
Date: 04/17/2000 23:22:31
Hi Werner,
OK, correct me if I'm wrong in any of the assumptions I'm making. What it
sounds like you want to be able to do is extract the texture itself from
the slice plane and map it onto an inventor object which you can then
manipulate all you want.. Volumizer should give you back a list of
geometry bound to a number of different textures, one for each brick. What
you want to do is create a single inventor object with the slice texture
applied to that object. The problem is: how do you extract the slice
texture to use within Inventor? You definitely don't want to maintain one
Inventor object for each brick your slicing plane intersects..
So it seems to me that your best bet is to render the slicing plane into
an offscreen buffer, using a camera position and projection to align the
slicing plane to the viewport. Have a look at the SoOffscreenRenderer
class provided with Inventor. You should be able to use the getBuffer()
method of this class to retrieve the texture from the buffer, and then
create an SoTexture to hold the results. You'll no longer need the
original geometry - you can just create a single quad that covers the
texture, if you want.
I hope that helps. As for why you're not getting any geometry out of
Volumizer, I'm not sure what might be happening. Can you demonstrate the
problem that you're having in a smaller example (like the voglMPR demos or
the Inventor demo code?)
Dave
On Fri, 14 Apr 2000, Werner Wohlfahrter wrote:
> Hi,
>
> you are right, having more context information helps finding solutions for
> problems.
>
> My task is finding new ways to interact with volume data. I am working in an
> virtual environment using a Barco Virtual Table, magnetic tracker,
> Studierstube (http://www.cg.tuwien.ac.at/research/vr/studierstube/) and
> Volumizer.
>
> Studierstube is an augmented reality framework build on top of OpenInventor
> which provides stereo vision and 2 handed interaction using a personal
> interaction panel (PIP) in the one hand and a pen in the other.
> The Pen and the PIP are tracked.
> The PIP is a see-through plastic palette on which the virtual menus are
> displayed. (Think of a painter who holds a painters palette in the left and a
> brush in his right.)
> Volumizer is used to display the Volume data (surprise :). It is encapsulated
> in OpenInventor Nodes having a renderAction inside which is used by
> OpenInventor when traversing the sceneGraph.
> Using these tools enables me to display tiff and raw format volume data on the
> virtual table.
> I mapped a button and some sliders on the PIP where the button enables or
> disables Volumizers lookup-table and the sliders set the center and the width
> to get different displays.
> If you stick the pen into the volume and hold the pen's button down the volume
> will follow the pens movement.
> If you turn over the PIP the virtual menu disappears and you use the PIP as a
> cutting plane by sweeping through the volume. I am also able to fix cutting
> planes, move the volume and fix another one which is a very natural way of
> defining a volume of interest.
> Now I try to grab the texture of such a cutting plane and stick it somewhere
> on the virtual table. Imagine xray sheets on a doctors lightingwall.... These
> textures should be mapped on an OpenInventor Object (SoIndexedFace Set,
> SoCube) which is pickable and therefore moveable. If this would work I could
> set different cutting planes, getting different "xrays" and still have the 3d
> volume beside it .... which would be cool.
>
> So my problem now is to get the texture out of the volume and into an
> OpenInventor Object.
>
>
> I tried to run polygonizeMPR() using C3F_V3F and C4F_V3F but it still doesn't
> work.
>
> I also got a good hint from Manfred. It makes sense to take care of
> interleavedArrayFormat from the beginning not only before using the
> polygonizeMPR() function..... I did not check that yet.
>
> Hope this context information gives you a deeper understanding of my problem.
> Thanks for all your help. If you have any good ideas how to solve this problem
> - i would REALLY appreciate
> it!
>
> thanks ww ;)
>
>
>
> Dave Akers wrote:
>
> > Hi Werner,
> >
> > There are a couple of things you need to know about MPR in 2D texturing
> > mode. What you get back in this case is a whole bunch of polygon-pairs
> > associated with the bricks of the current brickset. The two polygons in
> > each pair have identical vertex information, but they are binned in
> > different bricks and have different per-vertex colorings. The two polygons
> > in each pair are drawn on top of each other, and the colors are used as
> > weights in the blending process. Make sense?
> >
> > So the result of all of this is that you absolutely must use C3F_V3F or
> > C4F_V3F as your interleavedArray type for MPR and 2D texturing. (You'll
> > notice that the voglMPR demos use C4F_V3F.) That would explain why you
> > would be getting strange results from the call to polygonizeMPR().
> >
> > You may also be confused about the way the texture mapping works in
> > Volumizer. You asked where the texture was stored when using an
> > interleavedArrayFormat without a T3F component to it. In this case,
> > Volumizer uses texgen in order to set up the texture coordinate system
> > implicitly from the vertex coordinates. So just before each brick is
> > bound, there is a call to voAppearanceActions::texgenSetEquation(), which
> > sets up the OpenGL texgen equations depending on whether 2-D or 3-D
> > textures are being used.
> >
> > That said, can you tell us more about what you're trying to do - not
> > just how you're trying to do it? Understanding the context in more detail
> > would give us a better idea of how to help you solve your problem..
> >
> > Thanks,
> >
> > Dave
> >
> > On Thu, 13 Apr 2000, Werner Wohlfahrter wrote:
> >
> > > Hi!
> > >
> > > I use Volumizer in combination with OpenInventor. I cutted my Volume
> > > using a SoClipPlane (works great!). Now I try to grab the texture of the
> > > cuttingPlane and map it on an OpenInventor Object.
> > > I think the following should work (please correct me if i'm wrong!):
> > > - create allVertexData
> > > - create aPolygonSetArray
> > > - xfmVox2TexCoords
> > > - polygonizeMPR using the planeEquation of SoClipPlane
> > > - grab the geometry data from the aPolygonSetArray
> > > - grab the texture data from the aPolygonSetArray
> > > - use SoCoordinate3 Object to store geometry
> > > - use SoTextureCoordinate2 to store texture
> > > - use SoNormal
> > > - use SoNormalBinding
> > > - use SoTextureCoordinateBinding
> > > - use So(Indexed)FaceSet
> > >
>
> --
> \|/
> @ @
> ======================================================oOO(_)OOo=====
> Werner Wohlfahrter
> Fraunhofer CRCG, Inc.
> 321 South Main St.
> Providence, RI 02903, USA
>
> phone : (+1) 401 453-6363 x110
> email : wwohlfah@crcg.edu, ww@cg.tuwien.ac.at
> url : http://www.crcg.edu/ww
> icq : 9611406
> =====================================================================
>
>
This archive was generated by hypermail 2b29 : Wed Apr 19 2000 - 11:32:42 PDT