Hi, Dirk Reiners wrote:
Hi, Madhavan wrote:Hi, Are Silhouette & Feature Line Extraction possible in OpenSG?There's very little that's not possible. ;)Can anybody provide some tips on that?OpenSG's Geometry is targeted at rendering with OpenGl. As such it is pretty low-level as far as Geometry data structures go, so there are no edges or other elements that typical geometry processing tools like OpenMesh have.So if you need a geometric representation of Silhouettes and feature lines, we don't have support for that, sorry.
Rendering silhouettes can be done (similiar to a toon shader) with the help of a MultiPassMaterial: first render as usual (if you want to see the whole geo), in the second pass set color to black (for outlining the silhouettes), use a LineChunk with width being at least 2, and a PolygonChunk for culling all front facing polygons and the backMode field set to GL_LINE.
If you want to extract features like those which come along with sudden changes in depth or the object's normals, you can first render your scene into a floating point texture (by either using the texCoords as position or the eye-space position itself). Because this is also a multipass approach, at least in OpenSG 1.x you need something like the FBOViewport for doing this. In the second pass you can work on this texture which now has all needed neighbouring information like depth etc.
Hope it helps a little Yvonne
That said, there are ways to just render them, based on GPU tricks. I
haven't done any of that, but there have been a whole bunch of
publications. One of the older ones is Ramesh Raskar 'Image precision
silhouette edges' or his 'Hardware support for non-photorealistic
rendering'. Find them on google scholar and check out the papers that
cite them, that should give you enough information to get it going.
I don't know anybody who's done NPR with OpenSG yet, anybody?
Dirk
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