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add same_length option to offset()

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Adrian Mariano 2022-04-11 20:17:15 -04:00
parent a51e091019
commit f75ff907c7
1 changed files with 28 additions and 6 deletions
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32
regions.scad
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@ -707,7 +707,7 @@ function _point_dist(path,pathseg_unit,pathseg_len,pt) =
// Function: offset()
// Usage:
// offsetpath = offset(path, [r=|delta=], [chamfer=], [closed=], [check_valid=], [quality=])
// offsetpath = offset(path, [r=|delta=], [chamfer=], [closed=], [check_valid=], [quality=], [same_length=])
// path_faces = offset(path, return_faces=true, [r=|delta=], [chamfer=], [closed=], [check_valid=], [quality=], [firstface_index=], [flip_faces=])
// Description:
// Takes a 2D input path, polygon or region and returns a path offset by the specified amount. As with the built-in
@ -727,7 +727,15 @@ function _point_dist(path,pathseg_unit,pathseg_len,pt) =
// some situations you may be able to decrease run time by setting quality to 0, which causes only
// segment ends to be checked.
// .
// For construction of polyhedra `offset()` can also return face lists. These list faces between
// When invalid segments are eliminated, the path length decreases. If you use chamfering or rounding, then
// the chamfers and roundings can increase the length of the output path. Hence points in the output may be
// difficult to associate with the input. If you want to maintain alignment between the points you
// can use the `same_length` option. This option requires that you use `delta=` with `chamfer=false` to ensure
// that no points are added. When points collapse to a single point in the offset, the output includes
// that point repeated to preserve the correct length.
// .
// Another way to obtain alignment information is to use the return_faces option, which can
// provide alignment information for all offset parameters: it returns a face list which lists faces between
// the original path and the offset path where the vertices are ordered with the original path
// first, starting at `firstface_index` and the offset path vertices appearing afterwords. The
// direction of the faces can be flipped using `flip_faces`. When you request faces the return
@ -741,9 +749,11 @@ function _point_dist(path,pathseg_unit,pathseg_len,pt) =
// closed = if true path is treate as a polygon. Default: False.
// check_valid = perform segment validity check. Default: True.
// quality = validity check quality parameter, a small integer. Default: 1.
// same_length = return a path with the same length as the input. Only compatible with `delta=`. Default: false
// return_faces = return face list. Default: False.
// firstface_index = starting index for face list. Default: 0.
// flip_faces = flip face direction. Default: false
// Example(2D,NoAxes):
// star = star(5, r=100, ir=30);
// #stroke(closed=true, star, width=3);
@ -812,12 +822,21 @@ function _point_dist(path,pathseg_unit,pathseg_len,pt) =
// square([40,20], center=true)));
// #linear_extrude(height=1.1) stroke(rgn, width=1);
// region(offset(rgn, r=-5));
// Example(2D,NoAxes): Using `same_length=true` to align the original curve to the offset. Note that lots of points map to the corner at the top.
// closed=false;
// path = [for(angle=[0:5:180]) 10*[angle/100,2*sin(angle)]];
// opath = offset(path, delta=-3,same_length=true,closed=closed);
// stroke(path,closed=closed,width=.3);
// stroke(opath,closed=closed,width=.3);
// color("red") for(i=idx(path)) stroke([path[i],opath[i]],width=.3);
function offset(
path, r=undef, delta=undef, chamfer=false,
closed=false, check_valid=true,
quality=1, return_faces=false, firstface_index=0,
flip_faces=false
flip_faces=false, same_length=false
) =
assert(!(same_length && return_faces), "Cannot combine return_faces with same_length")
is_region(path)?
assert(!return_faces, "return_faces not supported for regions.")
let(
@ -829,6 +848,7 @@ function offset(
:
let(rcount = num_defined([r,delta]))
assert(rcount==1,"Must define exactly one of 'delta' and 'r'")
assert(!same_length || (is_def(delta) && !chamfer), "Must specify delta, with chamfer=false, when same_length=true")
assert(is_path(path), "Input must be a path or region")
let(
chamfer = is_def(r) ? false : chamfer,
@ -917,8 +937,10 @@ function offset(
_makefaces(
flip_faces, firstface_index, good,
pointcount, closed
)
) return_faces? [edges,faces] : edges;
),
final_edges = same_length ? select(edges, [0,each list_head (cumsum([for(g=good) g?1:0]))])
: edges
) return_faces? [edges,faces] : final_edges;