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| 21:06.35 | pier | Hi brlcad |
| 21:30.57 | brlcad | howdy |
| 21:47.42 | pier | hi.. |
| 21:48.01 | pier | I am having a look at the g-dxf.c code |
| 21:48.34 | pier | and wondering where to look for the db_walk_tree function source |
| 21:49.38 | brlcad | eep, you hopefully don't need to follow db_walk_tree beyone understanding that it walks the database geometry tree |
| 21:49.49 | brlcad | regardless, it's in src/librt/db_tree.c |
| 21:50.33 | brlcad | parallel tree walker |
| 21:51.16 | pier | looks like this function does a lot of very important things |
| 21:52.14 | pier | Does it brows the input file pointed by dbip? |
| 21:53.13 | brlcad | it does |
| 21:54.11 | brlcad | it walks through all the geometry in a directory |
| 21:54.32 | brlcad | by itself, that is all that it does |
| 21:54.55 | brlcad | what makes it useful, though, is that you provide it function pointers |
| 21:55.43 | pier | nmg_booltree etc? |
| 21:55.44 | brlcad | those callback functions are called when various geometry are encountered |
| 21:58.03 | pier | so these functions get out triangles from the shapes in the db tree? |
| 21:58.46 | brlcad | what are you looking at specifically? |
| 21:59.15 | brlcad | more than likely if db_walk_tree is being used with nmg evaluation, then yes.. the geometry is being extracted as triangles |
| 21:59.50 | pier | I was just trying to work out the way the code works but the deeper I go the harder it gets |
| 22:01.36 | pier | in order to learn something more about the way you get the shell surface from a boolean combination of solid shapes |
| 22:01.42 | brlcad | you're starting with a pretty complicated converter to begin with |
| 22:02.22 | brlcad | all the nmg_* routines basically do the "get the shell surface from a boolean combination of solid shapes" |
| 22:02.25 | pier | ... positive.. |
| 22:03.36 | brlcad | so you presumably were looking at: |
| 22:03.40 | brlcad | <PROTECTED> |
| 22:03.40 | brlcad | <PROTECTED> |
| 22:03.40 | brlcad | <PROTECTED> |
| 22:03.40 | brlcad | <PROTECTED> |
| 22:03.40 | brlcad | <PROTECTED> |
| 22:03.42 | brlcad | <PROTECTED> |
| 22:03.44 | brlcad | <PROTECTED> |
| 22:03.49 | pier | yes |
| 22:04.25 | brlcad | when you open a geometry database, you're create a directory of the contents |
| 22:04.37 | brlcad | that eventually gets you the dbip |
| 22:04.56 | pier | ok |
| 22:05.09 | pier | I get it |
| 22:05.16 | brlcad | the db_walk_tree function there has two callbacks |
| 22:05.39 | brlcad | whild it's walking the directory, it encounters combinations/regions and primitives |
| 22:05.48 | brlcad | the primitives are "leaf nodes" |
| 22:06.09 | pier | go on please |
| 22:06.11 | brlcad | when it finds a combination/region, db_walk_tree() calls do_region_end() |
| 22:06.25 | brlcad | when it finds a primitive, it calls nmg_booltree_leaf_tess() |
| 22:07.41 | brlcad | nmg_booltree_leaf_tess() is provided by a library and basically tesselates the object into triangles |
| 22:07.54 | pier | ok |
| 22:08.05 | brlcad | do_region_end() is presumably a function in the dxf converter that puts it all together |
| 22:11.21 | pier | I pondered your idea about getting plan views from a raycastin algorithm and I was trying to understand |
| 22:12.36 | pier | the dxf outputting code to see if that aim could have been achieved by modifying the g-dxf code |
| 22:14.25 | brlcad | i thought about that a little bit more as well, the route I'd think about to get a non-discretized answer would require adding a routine to all the primitives |
| 22:15.39 | brlcad | e.g. for the sphere primitive, there already exists a routine to evaluate/get the implicit for (the _shot() routine) and a polygonal explicit form (the _tess() routine) |
| 22:15.45 | pier | that somewhere finds the coordinates of all the objects in the db whose manipoulation I wouldn't like to get involved with |
| 22:16.33 | pier | ok but I got stuck when it comes to the hidden line removal |
| 22:16.53 | brlcad | if one added a _brep() routine or somesuch that returned the brep form, you could then rather easily directly extract exact spline projections |
| 22:19.17 | pier | say I got a pipe |
| 22:20.11 | brlcad | you mean a cylinder? |
| 22:20.25 | pier | which can be thought of as a union rcc1 (with R) - rcc2 (r<R) |
| 22:20.58 | pier | in a g file I ould retrieve the geometrical data of both |
| 22:20.59 | brlcad | ah, so an actual hollow pipe, got it |
| 22:21.04 | pier | yes |
| 22:21.44 | pier | rcc1 (lenght L) rcc2 (l>L) |
| 22:22.33 | pier | I could work out the maximum dimensions of the object |
| 22:22.56 | pier | Xmax Ymax Xmin Ymin to get a view port |
| 22:23.41 | pier | from whose points shoot perpendicoular rays |
| 22:24.15 | pier | am I on the right way? |
| 22:25.34 | brlcad | for a discretized method, sure |
| 22:25.55 | pier | mmm |
| 22:26.05 | pier | otherwise |
| 22:27.36 | pier | for a shape one should consider the edges and project them on a plane |
| 22:28.02 | brlcad | right |
| 22:28.35 | brlcad | that's the method i'm referring to, it's just a matter of how to "get the edge" |
| 22:28.39 | pier | in the case of a cylinder two ellipses joined by two lines tangent to botw of them |
| 22:29.18 | brlcad | you can get a discretized edge from ratracing (a pretty good one at that, but discretized nonetheless) and respline |
| 22:30.24 | brlcad | for non-discretized splines, you can get the edges/outlines etc .. but that's where I said that it'll require modifying the primitives themselves since there currently aren't routines to do this |
| 22:31.01 | brlcad | the first is more simple (and could even be tacked into g-dxf or wherever, but the latter is a "better" solution from a numerical standpoint |
| 22:32.11 | pier | for the sigle shapes (primitives) the projection shouldn't be hard as long as they are not concave |
| 22:33.43 | brlcad | some primitives will be very hard |
| 22:33.46 | brlcad | some not so hard |
| 22:33.49 | brlcad | at all |
| 22:34.06 | pier | yes the ellipsoid for instance |
| 22:34.49 | brlcad | the only hard part will be implementing the boolean evaluation |
| 22:35.33 | brlcad | we have booleans on implicits and triangles, but not brep splines |
| 22:35.48 | brlcad | even for generalized polygons |
| 22:35.48 | pier | yes |
| 22:36.17 | brlcad | it's more the amount of time/effort involved |
| 22:37.05 | brlcad | i'd gather it'd be a generous month or so to get splines in an rtedge fashion inside g-dxf |
| 22:37.37 | brlcad | 6+ months to get full brep support, maybe 2 or 3 for minimal |
| 22:37.48 | ``Erik | MEER ME |
| 22:37.50 | brlcad | and that's a lot of math |
| 22:37.50 | ``Erik | BEER |
| 22:37.58 | brlcad | ~beer ``Erik |
| 22:37.59 | ibot | ACTION deftly decants a fine Jever for ``Erik |
| 22:38.06 | ``Erik | heh, yelling typo's kinda spoiles the effect |
| 22:38.15 | pier | maybe for one who knows exactly what to do and where put hands |
| 22:38.24 | brlcad | yet conveniently still works when it's related to alcohol |
| 22:38.37 | ``Erik | wish I had me some of that |
| 22:38.43 | ``Erik | but, alas, I'm not allowed yet |
| 22:38.54 | brlcad | pier: that was factored in somewhat :) |
| 22:39.04 | pier | :) |
| 22:39.40 | pier | was thinking about matrix rotation to get ellipsoid projection on a plane but not sure |
| 22:41.52 | pier | ok I'll think it over... going to bed now. Have a nice day |
| 22:42.04 | brlcad | not so hard if you have brep |
| 22:42.24 | brlcad | it all ends up being transformations on the splines like how triangles get transformed |
| 22:47.06 | pier | put enough meat on the fire for me... risk going to get clogged up :) bye |
| 22:48.15 | brlcad | heh, cya |
| 22:48.56 | *** part/#brlcad pier (n=pier@151.56.220.10) |
| 23:48.31 | ``Erik | so how's the new gui going? |
| 23:51.44 | brlcad | no decent progress in dec |