Add a new processing stage to inject glyphs from extra sources. Add a basic Eszett/ß glyph, which I produced manually by using the image from https://xkcd.com/2586/, pulling out the beta symbol, and removing the tail

Author: pelson

xkcd-script/font/xkcd-script.otf

@@ -0,0 +1,112 @@
+# -*- coding: utf-8 -*-
+"""
+Extract hand-drawn glyphs from extras/ and convert them to SVG.
+
+Outputs go to ../generated/additional_chars/ and are consumed by pt6_derived_chars.py.
+"""
+import os
+import subprocess
+import tempfile
+import numpy as np
+from PIL import Image
+import fontforge
+
+OUT_DIR = '../generated/additional_chars'
+os.makedirs(OUT_DIR, exist_ok=True)
+
+UPSAMPLE = 12   # upscale factor before potrace; higher = more curve detail
+THRESHOLD = 160  # pixel value below which a pixel is considered ink
+
+
+def _clean_potrace_svg(raw_svg_path, clean_svg_path):
+    """Remove potrace artefacts from raw_svg_path and write clean_svg_path.
+
+    Potrace always emits a background rectangle covering the full canvas, plus
+    occasional single-pixel noise specks.  We load the SVG into FontForge,
+    drop those contours, and re-export so that pt6 receives a file containing
+    only the actual ink outlines.
+
+    Filtering rules (applied in order):
+      1. Background rectangle: <= 12 control points AND spans > 80% of the
+         full bounding box in both axes.
+      2. Noise specks: bbox smaller than 10% of the remaining ink extent in
+         both axes simultaneously.
+    """
+    scratch = fontforge.font()
+    g = scratch.createChar(-1, 'tmp')
+    g.importOutlines(raw_svg_path)
+
+    # Pass 1: drop background rectangle
+    full_bb = g.boundingBox()
+    full_w = full_bb[2] - full_bb[0]
+    full_h = full_bb[3] - full_bb[1]
+    pass1 = fontforge.layer()
+    for c in g.foreground:
+        cb = c.boundingBox()
+        span_w = (cb[2] - cb[0]) / full_w if full_w else 0
+        span_h = (cb[3] - cb[1]) / full_h if full_h else 0
+        if len(list(c)) <= 12 and span_w > 0.8 and span_h > 0.8:
+            continue
+        pass1 += c
+    g.foreground = pass1
+
+    # Pass 2: drop noise specks relative to ink extent
+    ink_bb = g.boundingBox()
+    ink_w = ink_bb[2] - ink_bb[0]
+    ink_h = ink_bb[3] - ink_bb[1]
+    ink = fontforge.layer()
+    for c in pass1:
+        cb = c.boundingBox()
+        if (cb[2] - cb[0]) < ink_w * 0.10 and (cb[3] - cb[1]) < ink_h * 0.10:
+            continue
+        ink += c
+    g.foreground = ink
+
+    scratch.save(clean_svg_path + '.sfd')  # FontForge can't export single-glyph SVG directly
+    # Export via generate — write to a temp SFD then export the glyph as SVG
+    g.export(clean_svg_path)
+    os.remove(clean_svg_path + '.sfd')
+
+
+def extract_symbol(arr, r0, r1, c0, c1, name):
+    """Crop glyph region, upsample, binarise, run potrace, clean, save SVG."""
+    crop = arr[r0:r1, c0:c1]
+    big = Image.fromarray(crop).resize(
+        (crop.shape[1] * UPSAMPLE, crop.shape[0] * UPSAMPLE),
+        Image.BILINEAR)
+    binary = (np.array(big) >= THRESHOLD).astype(np.uint8) * 255
+
+    with tempfile.TemporaryDirectory() as tmp:
+        png_path = os.path.join(tmp, f'{name}.png')
+        pbm_path = os.path.join(tmp, f'{name}.pbm')
+        raw_svg  = os.path.join(tmp, f'{name}_raw.svg')
+        Image.fromarray(binary, mode='L').save(png_path)
+        subprocess.check_call(['convert', png_path, '-threshold', '50%', pbm_path])
+        subprocess.check_call(['potrace', '-s', pbm_path, '-o', raw_svg])
+        svg_path = os.path.join(OUT_DIR, f'{name}.svg')
+        _clean_potrace_svg(raw_svg, svg_path)
+
+    print(f'  wrote {svg_path}')
+    return svg_path
+
+
+# ---------------------------------------------------------------------------
+# Hand-drawn extras (generator/extras/*.png)
+# Each file is a full-glyph image (no cropping needed).  RGBA images are
+# composited onto white before thresholding so transparent areas read as white.
+# A lower upsample factor is used since these images are already high-res.
+# ---------------------------------------------------------------------------
+
+EXTRAS_DIR = 'extras'
+
+EXTRAS = [
+    'eszett',   # ß U+00DF / ẞ U+1E9E source
+]
+
+print('Extracting hand-drawn extras...')
+for name in EXTRAS:
+    src_path = os.path.join(EXTRAS_DIR, f'{name}.png')
+    arr_extra = np.array(Image.open(src_path).convert('L'))
+    h, w = arr_extra.shape
+    extract_symbol(arr_extra, 0, h, 0, w, name)
+

xkcd-script/font/xkcd-script.sfd

@@ -5,6 +5,7 @@
 
 Reads the base SFD produced by pt4_svg_to_font.py, adds derived glyphs, saves.
 """
+import os
 import fontforge
 import psMat
 
@@ -351,6 +352,101 @@ def _accented(cp, base_name, mark_name, gap=20, x_adj=0):
     _accented(cp, base, '_macron_mark')
 
 
+# ---------------------------------------------------------------------------
+# Glyphs imported from xkcd comic images
+# ---------------------------------------------------------------------------
+
+_COMIC_CHARS_DIR = os.path.join(os.path.dirname(__file__), '../generated/additional_chars')
+
+
+def _import_comic_glyph(font, name, svg_path, target_top, weight_delta=0, y_clip=None):
+    """Import a pre-cleaned SVG (from pt5_additional_sources.py) and scale it
+    so the top of the ink reaches target_top in font units, preserving the
+    aspect ratio so any descender falls naturally below baseline.
+
+    weight_delta: passed to changeWeight() after scaling (positive = thicker).
+    y_clip: if given, clip the glyph at this y-coordinate using FontForge's
+    intersect() against a background rectangle, removing everything below y_clip.
+    Use y_clip=0 to clip at the baseline (removes descenders, seats the glyph
+    on the baseline with a natural edge rather than a raw image crop).
+    """
+    g = font.createChar(-1, f'_comic_{name}')
+    g.clear()
+    g.importOutlines(svg_path)
+
+    # Scale uniformly so the top of the ink reaches target_top
+    bb = g.boundingBox()
+    scale = target_top / bb[3]
+    g.transform(psMat.scale(scale))
+
+    # Translate to add left margin; vertical position follows naturally from scale
+    bb = g.boundingBox()
+    g.transform(psMat.translate(-bb[0] + 20, 0))
+
+    if weight_delta:
+        g.removeOverlap()
+        g.changeWeight(weight_delta)
+
+    if y_clip is not None:
+        # Clip at y_clip: keep only ink above y_clip.
+        # Place a filled rectangle covering [y_clip, +∞] in the background layer,
+        # then intersect() keeps only the foreground that overlaps that rectangle.
+        # FontForge uses clockwise winding for filled (outer) contours.
+        g.removeOverlap()
+        g.correctDirection()
+        clip_rect = fontforge.contour()
+        clip_rect += fontforge.point(-10000, 10000, True)   # top-left
+        clip_rect += fontforge.point(10000, 10000, True)    # top-right
+        clip_rect += fontforge.point(10000, y_clip, True)   # bottom-right
+        clip_rect += fontforge.point(-10000, y_clip, True)  # bottom-left
+        clip_rect.closed = True
+        bg = fontforge.layer()
+        bg += clip_rect
+        g.background = bg
+        g.intersect()
+
+    g.correctDirection()
+    g.removeOverlap()
+    g.addExtrema()
+
+    bb = g.boundingBox()
+    g.width = int(round(bb[2] + 20))
+    return g
+
+
+# ß/ẞ source: hand-drawn glyph from extras/eszett.png, vectorised by pt0.
+_eszett_svg = os.path.join(_COMIC_CHARS_DIR, 'eszett.svg')
+if os.path.exists(_eszett_svg):
+    # ß  U+00DF  Latin Small Letter Sharp S — scaled to ascender height (like 'b')
+    _eszett_glyph = _import_comic_glyph(
+        font, 'eszett', _eszett_svg,
+        target_top=font['b'].boundingBox()[3] * 0.65,
+        weight_delta=15)
+    # Snap bottom to baseline so ß sits like a/e
+    _bb = _eszett_glyph.boundingBox()
+    if _bb[1] < 0:
+        _eszett_glyph.transform(psMat.translate(0, -_bb[1]))
+    _eszett = font.createMappedChar(0x00DF)
+    _eszett.clear()
+    for c in _eszett_glyph.foreground:
+        _eszett.foreground += c
+    _eszett.width = _eszett_glyph.width
+
+    # ẞ  U+1E9E  Latin Capital Letter Sharp S — scaled to capital height (like 'B')
+    _cap_eszett_glyph = _import_comic_glyph(
+        font, 'eszett_cap', _eszett_svg,
+        target_top=font['B'].boundingBox()[3] * 0.75,
+        weight_delta=15)
+    _bb = _cap_eszett_glyph.boundingBox()
+    if _bb[1] < 0:
+        _cap_eszett_glyph.transform(psMat.translate(0, -_bb[1]))
+    _cap_glyph = font.createMappedChar(0x1E9E)
+    _cap_glyph.clear()
+    for c in _cap_eszett_glyph.foreground:
+        _cap_glyph.foreground += c
+    _cap_glyph.width = _cap_eszett_glyph.width
+
+
 # ---------------------------------------------------------------------------
 # Save
 # ---------------------------------------------------------------------------

xkcd-script/font/xkcd-script.ttf

@@ -2,7 +2,7 @@
 """
 Apply font-wide properties: kerning, spacing, and any other metric tweaks.
 
-Reads the SFD produced by pt5_derived_chars.py (which has all glyphs),
+Reads the SFD produced by pt6_derived_chars.py (which has all glyphs),
 applies properties, saves.
 """
 import fontforge

xkcd-script/font/xkcd-script.woff

@@ -12,6 +12,7 @@ $RUN_CTXT python3 pt1_character_extraction.py
 $RUN_CTXT python3 pt2_character_classification.py
 $RUN_CTXT python3 pt3_ppm_to_svg.py
 $RUN_CTXT python3 pt4_svg_to_font.py
-$RUN_CTXT python3 pt5_derived_chars.py
-$RUN_CTXT python3 pt6_font_properties.py
-$RUN_CTXT python3 pt7_gen_reprod_font.py
+$RUN_CTXT python3 pt5_additional_sources.py
+$RUN_CTXT python3 pt6_derived_chars.py
+$RUN_CTXT python3 pt7_font_properties.py
+$RUN_CTXT python3 pt8_gen_reprod_font.py