Add Sierpiński arrowhead curve example

kantoniak · kantoniak · commit 29ba8f40bf26 · 2025-09-21T01:25:10.000-07:00
diff --git a/examples/README.md b/examples/README.md
@@ -15,4 +15,5 @@ You can preview output files in Inkscape with Ink/Stitch installed.
 ## Example list
 
 * `python-pystitch-helloworld`: Basic example, a small square
-* `python-pystitch-addblock`: Simplified syntax, multiple squares with color changing
+* `python-pystitch-addblock`: Simplified syntax, multiple squares with color changing
+* `python-pystitch-sierpinski`: Build's Sierpiński arrowhead curve of selected depth
diff --git a/examples/python-pystitch-sierpinski/main.py b/examples/python-pystitch-sierpinski/main.py
@@ -0,0 +1,61 @@
+from pathlib import Path
+from pystitch import EmbPattern, CONTINGENCY_TIE_ON_THREE_SMALL, CONTINGENCY_TIE_OFF_THREE_SMALL, CONTINGENCY_LONG_STITCH_SEW_TO
+from typing import List, Tuple
+from utils import parse_args, UNITS_PER_MM
+import math
+import pystitch
+
+args = parse_args(default_filename = f'out/{Path(__file__).parent.name}.jef')
+
+# Create and encode pattern
+SIDE_WIDTH = args.side_width * UNITS_PER_MM
+CURVE_ORDER = args.curve_order
+print(f'Curve order: {CURVE_ORDER}')
+
+
+def build_arrowhead_curve(order: int, segment_length: float) -> List[Tuple[float, float]]:
+  path = [(0.0, 0.0)]
+  angle = 60 if order % 2 == 1 else 0
+
+  def expand(symbol: str, depth: int):
+    if depth == 0:
+      return symbol
+    result = ''
+    for char in symbol:
+      if char == 'A':
+        result += 'B-A-B'
+      elif char == 'B':
+        result += 'A+B+A'
+      else:
+        result += char
+    return expand(result, depth - 1)
+
+
+  instructions = expand('A', order)
+  for cmd in instructions:
+    if cmd in 'AB':
+      x, y = path[-1]
+      dx = segment_length * math.cos(math.radians(angle))
+      dy = segment_length * math.sin(math.radians(angle))
+      path.append((x + dx, y - dy))
+    elif cmd == '+':
+      angle += 60
+    elif cmd == '-':
+      angle -= 60
+  return path
+
+
+segment_length = SIDE_WIDTH / pow(2, CURVE_ORDER)
+print(f'Stitch length: {segment_length / UNITS_PER_MM}')
+if (segment_length > 6 * UNITS_PER_MM) or (1 * UNITS_PER_MM > segment_length):
+  print(f'Computed stitch length of {segment_length / UNITS_PER_MM} mm is out of recommended range 1-6 mm.')
+
+pattern = EmbPattern()
+pattern.add_block(build_arrowhead_curve(CURVE_ORDER, segment_length), "red")
+pattern.move_center_to_origin()
+pystitch.write(pattern, args.output, settings = {
+    'max_stitch': segment_length + 1, # Forces acceptable stitch length, the value might be outside of range supported by the machine,
+    'long_stitch_contingency': CONTINGENCY_LONG_STITCH_SEW_TO,
+    'tie_on': CONTINGENCY_TIE_ON_THREE_SMALL, # Tie-on stitches before the pattern
+    'tie_off': CONTINGENCY_TIE_OFF_THREE_SMALL, # Tie-off stitches after the pattern
+  })
diff --git a/examples/python-pystitch-sierpinski/out/.gitkeep b/examples/python-pystitch-sierpinski/out/.gitkeep
diff --git a/examples/python-pystitch-sierpinski/utils.py b/examples/python-pystitch-sierpinski/utils.py
@@ -0,0 +1,30 @@
+from argparse import ArgumentParser
+import os
+
+UNITS_PER_MM = 10
+
+def parse_args(default_filename: str = 'out/out.jef'):
+  ALLOWED_EXTENSIONS = [
+    '.dst',  # Tajima Embroidery Format
+    '.exp',  # Melco Expanded Embroidery Format
+    '.gcode',  # gcode Format, Text File
+    '.jef',  # Janome Embroidery Format
+    '.pec',  # Brother Embroidery Format
+    '.pes',  # Brother Embroidery Format
+    '.tbf',  # Tajima Embroidery Format
+    '.u01',  # Barudan Embroidery Format
+    '.vp3',  # Pfaff Embroidery Format
+    '.xxx'   # Singer Embroidery Format
+  ]
+
+  parser = ArgumentParser(description="Generate an embroidery design.")
+  parser.add_argument('-o', '--output', type=str, default=default_filename, help=f"Output file path. {default_filename} by default")
+  parser.add_argument('-d', '--curve-order', type=int, default=5, help="Curve order. 5 by default")
+  parser.add_argument('-s', '--side-width', type=float, default=60, help="Side width, in mm. 60 mm by default")
+  args = parser.parse_args()
+
+  _, ext = os.path.splitext(args.output)
+  if ext.lower() not in ALLOWED_EXTENSIONS:
+    raise ValueError(f"Invalid file extension '{ext}'. Allowed extensions: {ALLOWED_EXTENSIONS}")
+
+  return args
