NAME
Math::PlanePath::R5DragonMidpoint -- R5 dragon curve midpoints
SYNOPSIS
use Math::PlanePath::R5DragonMidpoint;my $path = Math::PlanePath::R5DragonMidpoint->new;my ($x, $y) = $path->n_to_xy (123);
DESCRIPTION
This is midpoints of the R5 dragon curve by Jorg Arndt,
31--30 11| |32 29 10| |51--50 35--34--33 28--27--26 9| | | |52 49 36--37--38 23--24--25 8| | | |55--54--53 48--47--46 41--40--39 22 7| | | |56--57--58 63--64 45 42 19--20--21 6| | | | | |81--80 59 62 65 44--43 18--17--16 11--10 5| | | | | | | |82 79 60--61 66--67--68 15 12 9 4| | | | | |..-83 78--77--76 71--70--69 14--13 8-- 7-- 6 3| | |75 72 3-- 4-- 5 2| | |74--73 2 1|0-- 1 <- Y=0^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 X=0 1 2 3
The points are the middle of each edge of the "R5DragonCurve", rotated -45 degrees, shrunk by sqrt(2). and shifted to the origin.
*--11--* *--7--* R5DragonCurve| | | | and its midpoints12 10 8 6| | | |*--17--*--13--*--9--*--5--*| | | |18 16 14 4| | | |..-* *--15--* *--3--*|2|+--1--*
Arms
Multiple copies of the curve can be selected, each advancing successively. Like the main "R5DragonCurve" this midpoint curve covers 1/4 of the plane and 4 arms rotated by 0, 90, 180, 270 degrees mesh together perfectly. With 4 arms all integer X,Y points are visited.
"arms => 4" begins as follows. N=0,4,8,12,16,etc is the first arm (the same shape as the plain curve above), then N=1,5,9,13,17 the second, N=2,6,10,14 the third, etc.
arms=>4 76--80-... 6|72--68--64 44--40 5| | |25--21 60 48 36 4| | | | |29 17 56--52 32--28--24 75--79 3| | | | |41--37--33 13-- 9-- 5 12--16--20 71 83 2| | | | |45--49--53 6-- 2 1 8 59--63--67 ... 1| | | |... 65--61--57 10 3 0-- 4 55--51--47 <- Y=0| | | | |81 69 22--18--14 7--11--15 35--39--43 -1| | | | |77--73 26--30--34 54--58 19 31 -2| | | | |38 50 62 23--27 -3| | |42--46 66--70--74 -4|...-82--78 -5^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^-6 -5 -4 -3 -2 -1 X=0 1 2 3 4 5
FUNCTIONS
See "FUNCTIONS" in Math::PlanePath for behaviour common to all path classes.
- "$path = Math::PlanePath::R5DragonMidpoint->new ()"
-
Create and return a new path object.
- "($x,$y) = $path->n_to_xy ($n)"
-
Return the X,Y coordinates of point number
$non the path. Points begin at 0 and if"$n < 0"then the return is an empty list.Fractional positions give an X,Y position along a straight line between the integer positions.
- "$n = $path->n_start()"
-
Return 0, the first N in the path.
Level Methods
- "($n_lo, $n_hi) = $path->level_to_n_range($level)"
-
Return
"(0, 5**$level - 1)", or for multiple arms return"(0, $arms *5**$level - 1)".There are 5^level segments comprising the curve, or arms*5^level when multiple arms, numbered starting from 0.
FORMULAS
X,Y to N
An X,Y point can be turned into N by dividing out digits of a complex base 1+2i. At each step the low base-5 digit is formed from X,Y and an adjustment applied to move X,Y to a multiple of 1+2i ready to divide out.
A 10x10 table is used for the digit and adjustments, indexed by Xmod10 and Ymod10. There's probably an a*X+b*Y mod 5 or mod 20 for a smaller table. But in any case once the adjustment is found the result is
Ndigit = digit_table[X mod 10, Y mod 10] # low to highXm = X + Xadj_table [X mod 10, Y mod 10]Ym = Y + Yadj_table [X mod 10, Y mod 10]new X,Y = (Xm,Ym) / (1+2i)= (Xm,Ym) * (1-2i) / 5= ((Xm+2*Ym)/5, (Ym-2*Xm)/5)
These X,Y reductions eventually reach one of the starting points for the four arms
X,Y endpoint Arm +---+---+------------ --- | 2 | 1 | Y=10, 0 0 +---+---+0, 1 1 | 3 | 0 | Y=0-1, 1 2 +---+---+-1, 0 3 X=-1 X=0
For arms 1 and 3 the digits must be flipped 4-digit, so 0,1,2,3,4 -> 4,3,2,1,0. The arm number and hence whether this flip is needed is not known until reaching the endpoint.
if arm oddthen N = 5^numdigits - 1 - N
If only some of the arms are of interest then reaching one of the other arm numbers means the original X,Y was outside the desired curve.
SEE ALSO
Math::PlanePath, Math::PlanePath::R5DragonCurve
Math::PlanePath::DragonMidpoint, Math::PlanePath::TerdragonMidpoint
HOME PAGE
<http://user42.tuxfamily.org/math-planepath/index.html>
LICENSE
Copyright 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020 Kevin Ryde
This file is part of Math-PlanePath.
Math-PlanePath is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version.
Math-PlanePath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with Math-PlanePath. If not, see <http://www.gnu.org/licenses/>.