Hello Carsten,
-------- Original-Nachricht --------
> Datum: Fri, 03 Jun 2011 16:15:03 -0500
> Von: Carsten Neumann <[email protected]>
> An: [email protected]
> Betreff: Re: [Opensg-users] Problems processing line strips
> Hello Daniel,
>
> I haven't had a chance to look at the code yet, thanks for providing the
> test file though!
>
> On 06/03/2011 10:43 AM, Daniel Weber wrote:
> > I'm using OpenSG2.0 to read line strips out of a .wrl file and process
> them afterwards. I've attached a sample file containing three line strips.
> In principle these line segments are connected, i.e., they represent a
> closed curve. I have some trouble with the whole process and I do not know if
> there are bugs or I'm missing something.
> >
> > 1) When reading the file, GL_LINES instead of GL_LINE_STRIPS are
> generated in the geometry core. A simple example shows the issue: At the end
> of
> the following code snipplet, the type of the geometry core is GL_LINES
> instead of GL_LINE_STRIP.
>
> hmm, that seems to be a case where the VRML loader/writer has taken a
> shortcut and just does not attempt to create LINE_STRIPS where it makes
> sense.
But writing and reading the geometry results in a different visualization. When
rendering the first node (before writing to "test.wrl") you can see a straight
line, while the one after the read results in a line stipple.
>
> > I fixed that in my application by traversing the generated scene graph
> and replacing all GL_LINES with GL_LINE_STRIP.
>
> that gives the expected visual result, but is a bit wasteful as you will
> have line segments of length 0 in the strip.
>
> > 2) In a second step I need to merge all geometry cores into one. As the
> geometry is spread over the whole the scenegraph and the GeometryMergeOp
> only works with direct children, I collected all geometry cores and put them
> "below" a group node ("newScene"). The merge operation works in principle,
> but it always results in two geometry cores: one with the merged geometry
> and another one. I assume that the "second" one is simply not deleted in the
> final step. Here is the code:
>
> that does indeed sound like a bug.
>
> > 3) In the third step, I call "createSharedIndex" in order to merge
> vertices that belong more than on line segment (these are the start- and
> end-vertices of the line strips.) With the attached file, only two of the
> three
> start-vertices are merged with the corresponding end-vertex. What may be the
> reason?)
> >
> > 4) Finally, I would like to make one linestrip out of the geometry. But
> the StipeGraphOp does not seem to work for linestrips (only tri- and
> quadstrips?)
>
> yes, the striper only handles triangle strips.
>
> In general the GraphOps are meant to perform optimizations that are
> applicable to all models so they may not necessarily give optimal
> results for specific cases like yours. That is not to say that the
> behaviour you are seeing indicates bugs that should be fixed, just that
> it may be hard to get the generic GraphOps to produce the exact result
> you are expecting.
> I would recommend considering to write your own GraphOp for the specific
> scene/optimization you require. Merging Geometry that is known to only
> contain line strips should not be very difficult and it's much easier to
> get the optimal representation you are looking for that way than by
> tweaking the generic code.
Yes, I did that already, but not as a OpenSG GraphOp. If I have some time, I
can transform the code into an OpenSG compatible one and make it available for
you.
Regards,
Daniel
>
> Cheers,
> Carsten
>
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