Marching squares: Difference between revisions
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See: [https://en.wikipedia.org/wiki/Marching_squares Marching squares]
=={{header|11l}}==
{{trans|Wren}}
<syntaxhighlight lang="11l">
-V
DIR_E = ( 1, 0)
DIR_NE = ( 1, 1)
DIR_N = ( 0, 1)
DIR_NW = (-1, 1)
DIR_W = (-1, 0)
DIR_SW = (-1, -1)
DIR_S = ( 0, -1)
DIR_SE = ( 1, -1)
F path_str(origin_x, origin_y, directions)
-V :dirn = [:DIR_E = ‘E’,
:DIR_NE = ‘NE’,
:DIR_N = ‘N’,
:DIR_NW = ‘NW’,
:DIR_W = ‘W’,
:DIR_SW = ‘SW’,
:DIR_S = ‘S’,
:DIR_SE = ‘SE’]
R ‘X: ’origin_x‘, Y: ’origin_y‘, Path: ’directions.map(d -> @:dirn[d])
T MarchingSquares
. Int width, height
. [Int] data
F (width, height, data)
.width = width
.height = height
.data = copy(data)
. F is_set(x, y)
I x <= 0 | x > .width | y <= 0 | y > .height
R 0B
R .data[(y - 1) * .width + (x - 1)] != 0
. F value(x, y)
V sum = 0
I .is_set(x, y) {sum [|]= 1}
I .is_set(x + 1, y) {sum [|]= 2}
I .is_set(x, y + 1) {sum [|]= 4}
I .is_set(x + 1, y + 1) {sum [|]= 8}
R sum
. F identify_perimeter_(=initial_x, =initial_y)
I initial_x < 0 {initial_x = 0}
I initial_x > .width {initial_x = .width}
I initial_y < 0 {initial_y = 0}
I initial_y > .height {initial_y = .height}
V initial_value = .value(initial_x, initial_y)
I initial_value C (0, 15)
X.throw RuntimeError(‘Supplied initial coordinates (#., #.) do not lie on a perimeter.’.format(initial_x, initial_y))
[IVec2] directions
V x = initial_x
V y = initial_y
V previous = (0, 0)
L
IVec2 direction
S .value(x, y)
1, 5, 13
direction = :DIR_N
2, 3, 7
direction = :DIR_E
4, 12, 14
direction = :DIR_W
8, 10, 11
direction = :DIR_S
6
direction = I previous == :DIR_N {:DIR_W} E :DIR_E
9
direction = I previous == :DIR_E {:DIR_N} E :DIR_S
E
X.throw RuntimeError(‘Illegal state.’)
directions.append(direction)
x += direction.x
y -= direction.y
previous = direction
I x == initial_x & y == initial_y
L.break
R path_str(initial_x, -initial_y, directions)
F identify_perimeter()
V size = .width * .height
L(i) 0 .< size
I .data[i] != 0
R .identify_perimeter_(i % .width, i I/ .width)
V example = [
0, 0, 0, 0, 0,
0, 0, 0, 0, 0,
0, 0, 1, 1, 0,
0, 0, 1, 1, 0,
0, 0, 0, 1, 0,
0, 0, 0, 0, 0
]
V ms = MarchingSquares(5, 6, example)
print(ms.identify_perimeter())
</syntaxhighlight>
{{out}}
<pre>
X: 2, Y: -2, Path: [S, S, E, S, E, N, N, N, W, W]
</pre>
=={{header|J}}==
Line 11 ⟶ 123:
This is a partial implementation, see the talk page for some discussion of the untouched issues.
<
step2=: {{(($y)#:i.$y) {{<x step2a y{::LUT}}"1 0 y}}
step2a=: {{ if. #y do. x+"1 y else. y end. }}
Line 49 ⟶ 161:
end.
r,<~.c
}}</
Task example:
<
img
1 1
Line 69 ⟶ 181:
│2 4│
│1 3│
└───┘</
Here, <code>img</code> is a bitmap. We pad the bitmap by surrounding it with zeros during processing. The box at the end contains a contour corresponding to the bitmap. Here, the first column represents row number (row 0 at the top) and the second column represents column number (column 0 at the left). Each contour represents a closed loop (so the final coordinate pair would connect with the first coordinate pair).
While the above implementation is incomplete, it seems to adequately handle an oval of cassini with focal points at X=1, -1 and Y=0:
<syntaxhighlight lang="j">a=: 1
X=: |:Y=:201#"0]0.02*i:100
Z0=: (*:(*:X)+(*:Y)) + (_2*(*:a)*X -&*: Y) + *:a
Z=: (Z0>:0.8)*Z0<:1.2
C=: unwind step2 step1 Z</syntaxhighlight>
Here, Z is a bitmap, and C is a list of three contours (one with 336 distinct coordinate pairs, and two with 134 distinct coordinate pairs) which surround that bitmap. These can be inspected (after <code>require'viewmat'</code>) with <code>viewmat Z</code> and <code>viewmat 1 (<"1;C)} 200 200$0</code>, and look plausible.
(Presumably the above implementation would fail if a threshold had been picked such that the bitmap exhibited a saddlepoint at the origin.)
=={{header|Julia}}==
Uses the marching squares algorithm: see github.com/JuliaGeometry/Contour.jl/blob/master/src/Contour.jl
See the discussion page for the Oval of Cassini example
<
import GLMakie as GM # GLMakie also defines Contour so import, not using
Line 112 ⟶ 236:
GM.lines!(ovalxs3, ovalys3, color = :lightgreen, linewidth = 4)
GM.display(oplot)
</
<pre>
points = [(3, 4), (4, 3), (4, 2), (4, 1), (3, 0), (2, 1), (2, 1), (1, 2), (1, 3), (2, 4), (3, 4)]
Line 119 ⟶ 243:
=={{header|Lua}}==
Based on the Phix and Wren solutions.
<
local Directions = { -- clockwise from North
N = {x= 0, y=-1},
Line 215 ⟶ 339:
msMain (1, example)
</
<pre>
root: x=1 y=2
Line 222 ⟶ 346:
positions: {1,2, 2,2, 2,3, 3,3, 4,3, 4,4, 5,4, 5,3, 6,3, 6,2, 7,2, 7,3, 6,3, 6,4, 6,5, 6,6, 7,6, 7,7, 6,7, 6,6, 5,6, 4,6, 4,5, 3,5, 3,6, 2,6, 2,7, 1,7, 1,6, 2,6, 2,5, 2,4, 2,3, 1,3, }
</pre>
=={{header|Perl}}==
{{trans|Raku}}
<syntaxhighlight lang="perl">use v5.36;
no warnings 'experimental::for_list';
use List::Util 'any';
use enum <E N W S>;
sub X ($a,$b) { my @c; for my $aa (0..$a) { for my $bb (0..$b) { push @c, $aa, $bb } } @c }
sub identify_perimeter(@data) {
for my ($x,$y) (X $#{$data[0]}, $#data) {
next unless $data[$y][$x] and $data[$y][$x] != 0;
my ($path,$cx,$cy,$d,$p) = ('', $x, $y);
do {
my $mask;
for my($dx,$dy,$b) (0,0,1, 1,0,2, 0,1,4, 1,1,8) {
my ($mx, $my) = ($cx+$dx, $cy+$dy);
$mask += $b if $mx>1 and $my>1 and $data[$my-1][$mx-1] != 0
}
$d = N if any { $mask == $_ } (1, 5,13);
$d = E if any { $mask == $_ } (2, 3, 7);
$d = W if any { $mask == $_ } (4,12,14);
$d = S if any { $mask == $_ } (8,10,11);
$d = $p == N ? W : E if $mask == 6;
$d = $p == E ? N : S if $mask == 9;
$path .= $p = (<E N W S>)[$d];
$cx += (1, 0,-1,0)[$d];
$cy += (0,-1, 0,1)[$d];
} until $cx == $x and $cy == $y;
return $x, -$y, $path
}
exit 'That did not work out...';
}
my @M = ([0, 0, 0, 0, 0],
[0, 0, 0, 0, 0],
[0, 0, 1, 1, 0],
[0, 0, 1, 1, 0],
[0, 0, 0, 1, 0],
[0, 0, 0, 0, 0]);
printf "X: %d, Y: %d, Path: %s\n", identify_perimeter(@M);</syntaxhighlight>
{{out}}
<pre>X: 2, Y: -2, Path: SSESENNNWW</pre>
=={{header|Phix}}==
Based on the same code as the Wren example.
<!--<
<span style="color: #008080;">with</span> <span style="color: #008080;">javascript_semantics</span>
<span style="color: #008080;">enum</span> <span style="color: #000000;">E</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">N</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">W</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">S</span>
Line 279 ⟶ 450:
<span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"X: %d, Y: %d, Path: %s\n"</span><span style="color: #0000FF;">,</span><span style="color: #000000;">identifyPerimeter</span><span style="color: #0000FF;">(</span><span style="color: #000000;">example</span><span style="color: #0000FF;">))</span>
<!--</
{{out}}
<pre>
Line 286 ⟶ 457:
=={{header|Python}}==
<
from skimage import measure
Line 301 ⟶ 472:
contours = round(measure.find_contours(example, 0.1))[0]
print('[', ', '.join([str((p[1], 5 - p[0])) for p in contours]), ']')
</
<pre>
[ (3.0, 0.0), (2.0, 1.0), (2.0, 1.0), (1.0, 2.0), (1.0, 3.0), (2.0, 4.0), (3.0, 4.0), (4.0, 3.0), (4.0, 2.0), (4.0, 1.0), (3.0, 0.0) ]
</pre>
=={{header|Raku}}==
{{trans|Phix}}
<syntaxhighlight lang="raku" line># 20220708 Raku programming solution
enum <E N W S>;
my (@dx,@dy) := (1,0,-1,0), (0,-1,0,1);
my \example = ((0, 0, 0, 0, 0),
(0, 0, 0, 0, 0),
(0, 0, 1, 1, 0),
(0, 0, 1, 1, 0),
(0, 0, 0, 1, 0),
(0, 0, 0, 0, 0));
printf("X: %d, Y: %d, Path: %s\n", identifyPerimeter(example));
sub identifyPerimeter(\data) {
my (\height,\width) = { .elems, .first.elems }(data);
for ^width X ^height -> (\x,\y) {
if data[y;x] {
my ($cx,$cy,$directions,$previous) = x, y;
repeat {
my $mask;
for (0,0,1),(1,0,2),(0,1,4),(1,1,8) -> (\dx,\dy,\b) {
my ($mx,$my) = $cx+dx,$cy+dy;
$mask += b if all $mx>1, $my>1, data[$my-1;$mx-1]
}
given do given $mask {
when * ∈ ( 1, 5, 13 ) { N }
when * ∈ ( 2, 3, 7 ) { E }
when * ∈ ( 4, 12, 14 ) { W }
when * ∈ ( 8, 10, 11 ) { S }
when * ∈ ( 6 ) { $previous == N ?? W !! E }
when * ∈ ( 9 ) { $previous == E ?? N !! S }
} {
$directions ~= $previous = $_ ;
($cx,$cy) <<+=<< (@dx[.value], @dy[.value])
}
} until $cx==x and $cy==y ;
return x, -y, $directions
}
}
return -1, -1, "Not found!"
}</syntaxhighlight>
Output is the same as the Phix entry.
=={{header|Wren}}==
{{libheader|Wren-seq}}
This is a translation of the [http://www.tomgibara.com/computer-vision/marching-squares public domain Java code], written by Tom Gibara, which is linked to from the Wikipedia article. It also uses his example to test the code.
<
/* A direction in the plane. */
Line 526 ⟶ 744:
var ms = MarchingSquares.new(5, 6, example)
var path = ms.identifyPerimeter()
System.print(path)</
{{out}}
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