Hi Robert,
Thanks for your answer. It seems handling 3D meshes is more difficult
then I would have expected. However, I am not able to use geometry
shaders because the application is meant to run on a variety of
hardware, going as low as OpenGL 3.0 (which doesn't have them as far as
I know). Is there a way to do this in the conventional fixed function
pipeline? It works almost well enough, since this flat shading and
normal generation is the only problem it has.
Radu
On Tue 10 Jun 2014 04:00:39 AM EDT, Robert Osfield wrote:
HI Radu,
I wouldn't recommend using the SmoothingVisitor as it is written to
handle conventional surfaces, tetrahedral meshes are very much a
special case.
With modern GPU's there are alternatives to just doing a brute force
approach of generating all the triangles and normals, so if you can
target modern hardware that supports features like geometry shaders
then it would probably be best to look at custom solution just for
this case.
I haven't tried it before but if I were to tackle a tetrahedral mesh
right now I'd create an osg::Geometry with all the vertices you
require without duplicates and then use osg::DrawElementsUShort/UInt
to provide the primitives that reference these vertices. You would
then need the four corners of the tetrahedra as input to the geometry
shader and have it generate the 4 triangles required and the colours
for each face by computing the normals of the triangles and then
applying the lighting model. To get four vertices into geometry
shader you'd probably need to use LINE_STRIP_ADJACENCY primitive type
in osg::DrawElementsUShort/UInt.
An example of geometry shaders in action can be seen in one of the
code paths in osgforest example - here it converters a line segment
representing the trunk into a quad.
Robert.
On 9 June 2014 21:40, Radu Marin Butoi <[email protected]> wrote:
Hello everyone,
I am loading and displaying a tetrahedral mesh consisting of a list of
verticies and a list of tetrahedrons denoted by four indices of vertices. I
load these into a triangles primitive set as four triangles, one for each of
the faces of the tetra.
My first question is, is this method of representing a mesh inefficient?
There are two GL_TRIANGLEs for each of the interior triangles. The
performance seems to be fine. I have looked into libraries like VCG and
OpenMesh, but chose not to use them as I will need to only display and
select from the mesh, and no manipulation is needed. Also, I could not
figure out how to represent a VCG or OpenMesh mesh in a osg::Geometry.
One way to view the mesh in my application is as a solid. My second question
is how can I prevent this sort of effect from occurring (see attached, or
http://i.imgur.com/1t4xWy9.png)? I use a SmoothingVisitor to set normals
(and shading mode is set to flat), and since they are set per vertex the
normals do not point directly outwards. I've read around the mailing list
and it seems using BIND_PER_PRIMITIVE normal binding is deprecated and slow.
It was also mentioned to duplicate vertex entries and set different normals
like that, but I don't see how this would work on a mesh that is being
imported and built on the fly.
Thank you,
Radu
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