I don't understand why you think it needs tesselation to represent a
polygonal face with holes in it. OpenSCAD can handle such faces no problem
and tesselates them when triangles are required, such as for STL export.
The issue is that polyhedron can't create faces with holes.
The target of a sweep is a polyhedron. For this it interprets a vector of
polygons. The first polygon in this vector defines the starting face, and
the last the end face. Any two consecutive polygons define a piece of wall.
If I have a function that I can use to tesselate the first and last faces, I
can implement a sweep for any tube-like structures with holes, because it is
easy for me to find holes in polygons, but very expensive to implement an
earcut with holes for 2D-polygons.
Alternatively polyhedron could allow me to use (planar) faces with holes. In
this case, polyhedron could use internally the same function that a
linear_extrude obviously uses, when it extrudes a polygon with holes. BUT: I
don't see this coming soon, because it requires a tesselation of almost
planar faces in 3D. To use the suspected given 2D tesselation, the
implementation could employ some coordinate transformation like I just
presented in the other thread
http://forum.openscad.org/Rotation-question-tp24970p24992.html , then
project the almost planar face down to xy, and finally find the tesselation
by calling this ominous function. The problem of the "almost planar" will
stay. How will you define it? How much deviation will be allowed. How will
an "alternative construction" work?
However, even if polyhedron will accept polygons with holes some day, it
would be a nice-to-have, to get an explicite tesselation of a polygon with
holes from a built-in OpenSCAD function, just like cross() and norm()
operate over a list of numbers.
--
Sent from: http://forum.openscad.org/
nophead wrote
> I don't understand why you think it needs tesselation to represent a
> polygonal face with holes in it. OpenSCAD can handle such faces no problem
> and tesselates them when triangles are required, such as for STL export.
> The issue is that polyhedron can't create faces with holes.
The target of a sweep is a polyhedron. For this it interprets a vector of
polygons. The first polygon in this vector defines the starting face, and
the last the end face. Any two consecutive polygons define a piece of wall.
If I have a function that I can use to tesselate the first and last faces, I
can implement a sweep for any tube-like structures with holes, because it is
easy for me to find holes in polygons, but very expensive to implement an
earcut with holes for 2D-polygons.
Alternatively polyhedron could allow me to use (planar) faces with holes. In
this case, polyhedron could use internally the same function that a
linear_extrude obviously uses, when it extrudes a polygon with holes. BUT: I
don't see this coming soon, because it requires a tesselation of almost
planar faces in 3D. To use the suspected given 2D tesselation, the
implementation could employ some coordinate transformation like I just
presented in the other thread
<http://forum.openscad.org/Rotation-question-tp24970p24992.html> , then
project the almost planar face down to xy, and finally find the tesselation
by calling this ominous function. The problem of the "almost planar" will
stay. How will you define it? How much deviation will be allowed. How will
an "alternative construction" work?
However, even if polyhedron will accept polygons with holes some day, it
would be a nice-to-have, to get an explicite tesselation of a polygon with
holes from a built-in OpenSCAD function, just like cross() and norm()
operate over a list of numbers.
--
Sent from: http://forum.openscad.org/
