A rather laborious rendering of a wireframe graphic can be achieved with
JHS. If you would like to pursue it I have produced some small code and
some steps to use, shown below. The verb 'dp' is the main addition to your
work and the tgsjhs system. Another alternative, I gather, is Three.js with
JHS but I am not able to use it myself.
NB. catmullclark.ijs
NB. 12 3 2014
avg=: +/ % #
havePoints=: e."1/~ i.@#
catmullclark=: 3 :0
'mesh points'=. y
face_point=. avg"2 mesh{points
point_face=. |: mesh havePoints points
avg_face_points=. point_face avg@#"1 2 face_point
edges=. ~.,/ meshEdges=. mesh /:~@,"+1|."1 mesh
edge_face=. *./"2 edges e."0 1/ mesh
edge_center=. avg"2 edges{points
edge_point=. (0.5*edge_center) + 0.25 * edge_face +/ .* face_point
point_edge=. |: edges havePoints points
avg_mid_edges=. point_edge avg@#"1 2 edge_center
n=. +/"1 point_edge
'm3 m2 m1'=. (2,1,:n-3)%"1 n
new_coords=. (m1 * points) + (m2 * avg_face_points) + (m3 * avg_mid_edges)
pts=. face_point,edge_point,new_coords
c0=. (#edge_point)+ e0=. #face_point
msh=. (,c0+mesh),.(,e0+edges i. meshEdges),.((#i.)~/$mesh),.,e0+_1|."1
edges i. meshEdges
msh;pts
)
points=: _1+2*#:i.8
mesh=: 1 A."1 I.(,1-|.)8&$@#&0 1">4 2 1
rankinc =: ,@]$~-@[{.!.1 $@] NB. increase rank of y to x's value
mat =: 2&rankinc NB. increase rank of y to a matrix
dp =: 3 : 0
0 dp y
:
'msh pts' =. y
position =. x{Position
pts =. 30*pts
for_m. i. #msh do.
pu x
pt =. m{msh
x goto (mat position)+"1 pts{~pt{~0
pd x
x goto (mat position)+"1 pts{~pt{~1
x goto (mat position)+"1 pts{~pt{~2
x goto (mat position)+"1 pts{~pt{~3
end.
)
Below are the steps required.
0 launch jhs
1 in jhs enter the following commands
load'~user/projects/tgsjhs/tgsjhs.ijs'
coclass'tgsj'
load'~user/catmullclark.ijs' NB. or whatever you named the file
2 in a new tab enter the following address
http://127.0.0.1:65001/tgsj
3 in the field where you see 'fd 20', instead enter the following, eg.
dp catmullclark mesh;points
4 you can see various different views by moving the focus from the input
field
elsewhere and then using the arrow keys
5 if you want to try another mesh and points, first press the "Restart"
button
On Sun, Nov 30, 2014 at 10:18 AM, Raul Miller <[email protected]> wrote:
> The Catmull-Clark surface subdivision algorithm is a fun little algorithm:
>
> http://rosettacode.org/wiki/Catmull%E2%80%93Clark_subdivision_surface
> http://rosettacode.org/wiki/Catmull%E2%80%93Clark_subdivision_surface#J
>
> But there are other approaches to this task, and some of them require
> very different sorts of abstractions.
>
> But testing the result - especially when the result is not exactly
> equivalent but only visually similar - requires a way of visualizing
> the results. Basically, you need a decent rendering system (one that
> gives lighting effects to represent the orientation of surfaces).
>
> Meanwhile, I've not been spending much time with all of the
> possibilities we have here.
>
> What are some of the current best 3d rendering systems we have in J?
> (Bonus question: what does the data structure for a medium-grey or
> green cube look like, for each such system?)
>
> Thanks,
>
> --
> Raul
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
>
--
(B=)
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