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Add an option to hull2d_path

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RonaldoCMP 2021-05-05 23:41:02 +01:00
parent 4568fe76df
commit 8a2651cf3f
1 changed files with 16 additions and 10 deletions
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26
hull.scad
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@ -75,30 +75,36 @@ module hull_points(points, fast=false) {
function _backtracking(i,points,h,t,m) =
m<t || _is_cw(points[i], points[h[m-1]], points[h[m-2]]) ? m :
_backtracking(i,points,h,t,m-1) ;
function _backtracking(i,points,h,t,m,all) =
m<t || _is_cw(points[i], points[h[m-1]], points[h[m-2]],all) ? m :
_backtracking(i,points,h,t,m-1,all) ;
// clockwise check (2d)
function _is_cw(a,b,c) = cross(a-c,b-c)<-EPSILON*norm(a-c)*norm(b-c);
function _is_cw(a,b,c,all) =
all ? cross(a-c,b-c)<=0 :
cross(a-c,b-c)<-EPSILON*norm(a-c)*norm(b-c);
// Function: hull2d_path()
// Usage:
// hull2d_path(points)
// hull2d_path(points,all)
// Description:
// Takes a list of arbitrary 2D points, and finds the convex hull polygon to enclose them.
// Returns a path as a list of indices into `points`. May return extra points, that are on edges of the hull.
// Returns a path as a list of indices into `points`.
// When all==true, returns extra points that are on edges of the hull.
// Arguments:
// points - list of 2d points to get the hull of.
// all - when true, includes all points on the edges of the convex hull. Default: false.
// Example(2D):
// pts = [[-10,-10], [0,10], [10,10], [12,-10]];
// path = hull2d_path(pts);
// move_copies(pts) color("red") sphere(1);
// polygon(points=pts, paths=[path]);
//
// Code based on this method:
// https://www.hackerearth.com/practice/math/geometry/line-sweep-technique/tutorial/
//
function hull2d_path(points) =
function hull2d_path(points, all=false) =
assert(is_path(points,2),"Invalid input to hull2d_path")
len(points) < 2 ? [] :
let( n = len(points),
@ -109,7 +115,7 @@ function hull2d_path(points) =
k = 2,
h = [ip[0],ip[1]]; // current list of hull point indices
i <= n;
k = i<n ? _backtracking(ip[i],points,h,2,k)+1 : k,
k = i<n ? _backtracking(ip[i],points,h,2,k,all)+1 : k,
h = i<n ? [for(j=[0:1:k-2]) h[j], ip[i]] : [],
i = i+1
) if( i==n ) h ][0] )
@ -119,7 +125,7 @@ function hull2d_path(points) =
t = k+1,
h = lh; // current list of hull point indices
i >= -1;
k = i>=0 ? _backtracking(ip[i],points,h,t,k)+1 : k,
k = i>=0 ? _backtracking(ip[i],points,h,t,k,all)+1 : k,
h = [for(j=[0:1:k-2]) h[j], if(i>0) ip[i]],
i = i-1
) if( i==-1 ) h ][0] ;