Initial SewWriter implementation

README.md

@@ -115,6 +115,7 @@ Pystitch will write:
 * .jef (Janome Embroidery Format)
 * .pec (Brother Embroidery Format)
 * .pes (Brother Embroidery Format)
+* .sew (Janome Embroidery Format)
 * .tbf (Tajima Embroidery Format)
 * .u01 (Barudan Embroidery Format)
 * .vp3 (Pfaff Embroidery Format)

src/pystitch/SewWriter.py

@@ -0,0 +1,75 @@
+from typing import BinaryIO
+
+from pystitch.EmbConstant import (
+    COLOR_CHANGE,
+    COMMAND_MASK,
+    END,
+    JUMP,
+    STITCH,
+    TRIM,
+)
+from pystitch.EmbPattern import EmbPattern
+from pystitch.WriteHelper import write_int_16le, write_int_array_8
+
+HEADER_SIZE = 0x1D78
+STITCH_COUNT_OFFSET = 0x32
+
+
+def write(pattern: EmbPattern, f: BinaryIO, settings=None) -> None:
+    """
+    Write pattern to SEW-formatted binary buffer.
+
+    https://edutechwiki.unige.ch/en/Embroidery_format
+    https://community.kde.org/Projects/Liberty/File_Formats/Janome_Embroidery_Format#SEW_Format
+    """
+    # Write initial null bytes for header
+    f.write(bytes(HEADER_SIZE))
+    f.seek(0)
+
+    # Write color count
+    color_count = len(pattern.threadlist)
+    if color_count > 12:
+        raise ValueError("Cannot store more than 12 colors in SEW format")
+    write_int_16le(f, color_count)
+
+    # Write index of each color
+    for thread in pattern.threadlist:
+        if not thread.catalog_number:
+            continue
+        index = int(thread.catalog_number)
+        write_int_16le(f, index)
+
+    # Write stitch count for each color
+    f.seek(STITCH_COUNT_OFFSET, 0)
+    for block in pattern.get_as_colorblocks():
+        stitches, color = block
+        # This may produce lower than actual values
+        count = len([stitch for stitch in stitches if stitch[2] != COLOR_CHANGE])
+        write_int_16le(f, count)
+
+    # Write stitches
+    f.seek(HEADER_SIZE, 0)
+    xx = yy = 0
+    for stitch in pattern.stitches:
+        x, y, command = stitch
+        command &= COMMAND_MASK
+        dx = int(round(x - xx))
+        dy = int(round(y - yy))
+        xx += dx
+        yy += dy
+        if command == END:
+            break
+        elif command == STITCH:
+            write_int_array_8(f, [dx, -dy])
+        elif command == COLOR_CHANGE:
+            write_int_array_8(f, [0x80, 0x01])
+            write_int_array_8(f, [0x00, 0x00])
+        elif command == TRIM:
+            write_int_array_8(f, [0x80, 0x02])
+            write_int_array_8(f, [0x00, 0x00])
+        elif command == JUMP:
+            write_int_array_8(f, [0x80, 0x02])
+            write_int_array_8(f, [dx, -dy])
+
+    # End pattern
+    write_int_array_8(f, [0x80, 0x10])

src/pystitch/__init__.py

@@ -69,6 +69,7 @@
 import pystitch.QccReader as QccReader
 import pystitch.QccWriter as QccWriter
 import pystitch.SewReader as SewReader
+import pystitch.SewWriter as SewWriter
 import pystitch.ShvReader as ShvReader
 import pystitch.SpxReader as SpxReader
 import pystitch.StcReader as StcReader
@@ -280,6 +281,7 @@ def supported_formats():
             "mimetype": "application/x-sew",
             "category": "embroidery",
             "reader": SewReader,
+            "writer": SewWriter,
         }
     )
     yield (