From 863c410404fbff85a51a7014b77977eed0eb247a Mon Sep 17 00:00:00 2001 From: Adrian Mariano Date: Thu, 4 Mar 2021 18:34:17 -0500 Subject: [PATCH] doc tweaks for skin(), faster 2d hull() --- hull.scad | 85 +++++++++++++++++++++++++------------------------------ skin.scad | 54 +++++++++++++++++++++-------------- 2 files changed, 71 insertions(+), 68 deletions(-) diff --git a/hull.scad b/hull.scad index 0473715..fbfecdb 100644 --- a/hull.scad +++ b/hull.scad @@ -74,6 +74,15 @@ module hull_points(points, fast=false) { } + +function _backtracking(i,points,h,t,m) = + m 0, - polygon = ccw ? [tri[0],tri[1],tri[2]] : [tri[0],tri[2],tri[1]] - ) _hull2d_iterative(points, polygon, remaining); - - - -// Adds the remaining points one by one to the convex hull -function _hull2d_iterative(points, polygon, remaining, _i=0) = - (_i >= len(remaining))? polygon : let ( - // pick a point - i = remaining[_i], - // find the segments that are in conflict with the point (point not inside) - conflicts = _find_conflicting_segments(points, polygon, points[i]) - // no conflicts, skip point and move on - ) (len(conflicts) == 0)? _hull2d_iterative(points, polygon, remaining, _i+1) : let( - // find the first conflicting segment and the first not conflicting - // conflict will be sorted, if not wrapping around, do it the easy way - polygon = _remove_conflicts_and_insert_point(polygon, conflicts, i) - ) _hull2d_iterative(points, polygon, remaining, _i+1); - + : + assert(is_path(points,2)) + assert(len(points)>=3, "Point list must contain at least 3 points.") + let( n = len(points), + ip = sortidx(points) ) + // lower hull points + let( lh = + [ for( i = 2, + k = 2, + h = [ip[0],ip[1]]; // current list of hull point indices + i <= n; + k = i= -1; + k = i>=0 ? _backtracking(ip[i],points,h,t,k)+1 : k, + h = [for(j=[0:1:k-2]) h[j], if(i>0) ip[i]], + i = i-1 + ) if( i==-1 ) h ][0] ; + function _hull_collinear(points) = let( @@ -124,30 +141,6 @@ function _hull_collinear(points) = ) [min_i, max_i]; -function _find_conflicting_segments(points, polygon, point) = [ - for (i = [0:1:len(polygon)-1]) let( - j = (i+1) % len(polygon), - p1 = points[polygon[i]], - p2 = points[polygon[j]], - area = triangle_area(p1, p2, point) - ) if (area < 0) i -]; - - -// remove the conflicting segments from the polygon -function _remove_conflicts_and_insert_point(polygon, conflicts, point) = - (conflicts[0] == 0)? let( - nonconflicting = [ for(i = [0:1:len(polygon)-1]) if (!in_list(i, conflicts)) i ], - new_indices = concat(nonconflicting, (nonconflicting[len(nonconflicting)-1]+1) % len(polygon)), - polygon = concat([ for (i = new_indices) polygon[i] ], point) - ) polygon : let( - before_conflicts = [ for(i = [0:1:min(conflicts)]) polygon[i] ], - after_conflicts = (max(conflicts) >= (len(polygon)-1))? [] : [ for(i = [max(conflicts)+1:1:len(polygon)-1]) polygon[i] ], - polygon = concat(before_conflicts, point, after_conflicts) - ) polygon; - - - // Function: hull3d_faces() // Usage: // hull3d_faces(points) diff --git a/skin.scad b/skin.scad index 4d5e66d..7fad7b7 100644 --- a/skin.scad +++ b/skin.scad @@ -47,31 +47,29 @@ // profiles that you specify. It is generally best if the triangles forming your polyhedron // are approximately equilateral. The `slices` parameter specifies the number of slices to insert // between each pair of profiles, either a scalar to insert the same number everywhere, or a vector -// to insert a different number between each pair. To resample the profiles you can use set -// `refine=N` which will place `N` points on each edge of your profile. This has the effect of -// multiplying the number of points by N, so a profile with 8 points will have 8*N points after -// refinement. Note that when dealing with continuous curves it is always better to adjust the +// to insert a different number between each pair. +// . +// Resampling may occur, depending on the `method` parameter, to make profiles compatible. +// To force (possibly additional) resampling of the profiles to increase the point density you can set `refine=N`, which +// will multiply the number of points on your profile by `N`. You can choose between two resampling +// schemes using the `sampling` option, which you can set to `"length"` or `"segment"`. +// The length resampling method resamples proportional to length. +// The segment method divides each segment of a profile into the same number of points. +// This means that if you refine a profile with the "segment" method you will get N points +// on each edge, but if you refine a profile with the "length" method you will get new points +// distributed around the profile based on length, so small segments will get fewer new points than longer ones. +// A uniform division may be impossible, in which case the code computes an approximation, which may result +// in arbitrary distribution of extra points. See `subdivide_path` for more details. +// Note that when dealing with continuous curves it is always better to adjust the // sampling in your code to generate the desired sampling rather than using the `refine` argument. // . -// Two methods are available for resampling, `"length"` and `"segment"`. Specify them using -// the `sampling` argument. The length resampling method resamples proportional to length. -// The segment method divides each segment of a profile into the same number of points. -// A uniform division may be impossible, in which case the code computes an approximation. -// See `subdivide_path` for more details. -// // You can choose from four methods for specifying alignment for incommensurate profiles. // The available methods are `"distance"`, `"tangent"`, `"direct"` and `"reindex"`. // It is useful to distinguish between continuous curves like a circle and discrete profiles // like a hexagon or star, because the algorithms' suitability depend on this distinction. // . -// The "direct" and "reindex" methods work by resampling the profiles if necessary. As noted above, -// for continuous input curves, it is better to generate your curves directly at the desired sample size, -// but for mapping between a discrete profile like a hexagon and a circle, the hexagon must be resampled -// to match the circle. You can do this in two different ways using the `sampling` parameter. The default -// of `sampling="length"` approximates a uniform length sampling of the profile. The other option -// is `sampling="segment"` which attempts to place the same number of new points on each segment. -// If the segments are of varying length, this will produce a different result. Note that "direct" is -// the default method. If you simply supply a list of compatible profiles it will link them up +// The default method for aligning profiles is `method="direct"`. +// If you simply supply a list of compatible profiles it will link them up // exactly as you have provided them. You may find that profiles you want to connect define the // right shapes but the point lists don't start from points that you want aligned in your skinned // polyhedron. You can correct this yourself using `reindex_polygon`, or you can use the "reindex" @@ -79,12 +77,25 @@ // in the polyhedron---in will produce the least twisted possible result. This algorithm has quadratic // run time so it can be slow with very large profiles. // . +// When the profiles are incommensurate, the "direct" and "reindex" resampling them to match. As noted above, +// for continuous input curves, it is better to generate your curves directly at the desired sample size, +// but for mapping between a discrete profile like a hexagon and a circle, the hexagon must be resampled +// to match the circle. When you use "direct" or "reindex" the default `sampling` value is +// of `sampling="length"` to approximate a uniform length sampling of the profile. This will generally +// produce the natural result for connecting two continuously sampled profiles or a continuous +// profile and a polygonal one. However depending on your particular case, +// `sampling="segment"` may produce a more pleasing result. These two approaches differ only when +// the segments of your input profiles have unequal length. +// . // The "distance" and "tangent" methods work by duplicating vertices to create // triangular faces. The "distance" method finds the global minimum distance method for connecting two // profiles. This algorithm generally produces a good result when both profiles are discrete ones with // a small number of vertices. It is computationally intensive (O(N^3)) and may be // slow on large inputs. The resulting surfaces generally have curved faces, so be -// sure to select a sufficiently large value for `slices` and `refine`. +// sure to select a sufficiently large value for `slices` and `refine`. Note that for +// this method, `sampling` must be set to `"segment"`, and hence this is the default setting. +// Using sampling by length would ignore the repeated vertices and ruin the alignment. +// . // The `"tangent"` method generally produces good results when // connecting a discrete polygon to a convex, finely sampled curve. It works by finding // a plane that passed through each edge of the polygon that is tangent to @@ -92,9 +103,8 @@ // all of the tangent points from each other. It connects all of the points of the curve to the corners of the discrete // polygon using triangular faces. Using `refine` with this method will have little effect on the model, so // you should do it only for agreement with other profiles, and these models are linear, so extra slices also -// have no effect. For best efficiency set `refine=1` and `slices=0`. When you use refinement with either -// of these methods, it is always the "segment" based resampling described above. This is necessary because -// sampling by length will ignore the repeated vertices and break the alignment. +// have no effect. For best efficiency set `refine=1` and `slices=0`. As with the "distance" method, refinement +// must be done using the "segment" sampling scheme to preserve alignment across duplicated points. // . // It is possible to specify `method` and `refine` as arrays, but it is important to observe // matching rules when you do this. If a pair of profiles is connected using "tangent" or "distance"