IRC log for #brlcad on 20090307

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01:46.19 CIA-40 BRL-CAD: 03homovulgaris * r33968 10/brlcad/trunk/src/libpc/pcMathLF.h: lazy function implementations for Math parser
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03:53.34 yukonbob hello, cadheads
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08:04.34 joeedh hi. can brl-cad perform mesh CSG operations, resulting in new meshes?
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13:49.22 ``Erik_ joeedh: yes. Fire up mged, build your csg, then do 'facetize' on your region or comb and it should produce a new mesh with the csg evaluated
13:50.05 joeedh does it tesselate the geometry? if so, can you make it not do so?
13:50.22 ``Erik_ facetize is the command to tesselate
13:51.07 joeedh hrm. thanks.
13:51.24 ``Erik_ for 'real' (non-triangular) geometry, we do the CSG evaluation at raytrace time
13:52.22 ``Erik_ I believe that facetize on a csg tree of meshes will attempt to use the original triangle data unless it doens't make sense (like where the triangles are cut)
13:52.33 joeedh oh ok.
13:52.49 ``Erik_ of course, if you try to tesselate a mesh, it should just give you that same mesh back... :)
13:53.17 joeedh ah well I really meant "triangulate" in this context, my bad.
13:54.06 ``Erik_ hm, usually, meshes are considered to be of triangles... in OpenGL and DirectX, if you ask for a quad, it'll actually make you a tristrip or trifan
13:54.42 joeedh of course.
13:55.12 joeedh but you can still often have polygons in a lot of structures, they just tesselate to triangles as necassary.
13:55.19 joeedh ah arbritary polygons I mean
13:55.31 joeedh arbitrary* I think is the right spelling
13:56.04 ``Erik_ yeah, quad was just a specific example :) it's been a while since I've been in the guts of OGL, but back then a 500 sided polygon would still be reduced to triangles as soon as it was seen
13:56.46 joeedh yeah, it uses a triangle fan usually. opengl isn't really smart about tesselation properly, though i think there are better functions in glu.
13:57.04 ``Erik_ and, uh, 12 years ago, the cpu used to generate all those coplanar triangles wasn't worth it, so it used to be a speed boost to just use tristrip/trifan or VAR's were fashionable at the time
13:57.30 joeedh interesting.
13:58.23 ``Erik_ BRL-CAD's interactive display is wireframe with meshes getting every edge drawn, so jump in and experiment, there's useful visual feedback :) if you're looking for code stuff, the meshes are handled by src/librt/primitives/nmg/
13:59.03 joeedh oh thanks. yeah I was just wondering if we could someday use brl-cad's csg code in blender.
13:59.46 ``Erik_ ahh, heh, we actually have some .py scripts to talk to blender for certain things :)
14:00.00 joeedh really? what sort of scripts? that's interesting.
14:00.21 ``Erik_ lemme find a screenie of something
14:00.56 ``Erik_ http://brlcad.org/gallery/s/renderings/stryker_slat.jpg.html
14:01.20 ``Erik_ the vehicle was created in BRL-CAD, the flora in blender, and it was rendered using the ADRT/RISE system stashed in BRL-CAD
14:02.00 joeedh that's cool
14:02.43 ``Erik_ there's also a rendering of a glass cornelius somewhere, and one of the former BRL-CAD developers donated his NURBS code to blender iirc
14:02.45 joeedh I heard brl-cad uses a radial-edge brep for some things?
14:03.11 ``Erik_ uhm, I don't know, brlcad would be the guy to talk to, hwen he wakes up
14:03.33 ``Erik_ I know there're a couple brep primitives, one is old and sucky, and the other is in progress and uses openNURBS
14:04.49 ``Erik_ (frankly, I don't even know what "radial edge brep" means)
14:05.15 joeedh it's the original non-manifold boundary representation.
14:05.41 ``Erik_ *shrug* sorry, I don't know :)
14:06.22 joeedh it's not widely known. it's actually fairly difficult to get your hands on a paper about it, even.
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16:01.49 brlcad joeedh: mesh CSG ops are available in library form, through brl-cad's librt library
16:02.05 brlcad we have a generalized polygonal primitive type (n-manifold geometry) as well as a basic triangle primitive ("bag of triangles" geometry)
16:02.05 brlcad was awake, just busy pulling on an oar for hours then munching
16:03.43 brlcad joeedh: and it's not hard at all if you know where to look, especially if you have acm and ieee library access or old proceedings for siggraph, solid modeling, CAD, and other journals
16:03.52 brlcad (for papers on it)
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20:35.10 yukonbob hello, cadheads
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22:24.16 brlcad howdy yukonbob :)
22:24.46 brlcad extra quiet day

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