Gen Stroke Path

1#!/usr/bin/env python3
2"""gen-stroke-path.py — generalized draw-on path generator.
3
4Lays out ANY word in a single-line (pen-path) SVG font — Hershey/EMS — and emits
5one continuous-dash-revealable path `d`. The glyph data IS the pen path, so
6stroke-order reveal is exact by construction for any text, no per-word tuning.
7
8Usage: gen-stroke-path.py <font.svg> <text> <target_width_px> <baseline_y> <x0>
9Prints: the path `d` string + layout info on stderr.
10"""
11import re, sys
12
13# Windows sizes stdio to the ANSI code page (cp1252). These scripts emit UTF-8 on
14# every platform; say so rather than depending on the console's code page. Carry
15# `errors` across: reconfigure() resets it to "strict", and CPython deliberately gives
16# stderr "backslashreplace" so the diagnostic path can never itself raise.
17for _stream in (sys.stdout, sys.stderr):
18    if hasattr(_stream, "reconfigure"):
19        _stream.reconfigure(encoding="utf-8", errors=_stream.errors)
20
21font_path, text, target_w, baseline_y, x0 = (
22    sys.argv[1], sys.argv[2], float(sys.argv[3]), float(sys.argv[4]), float(sys.argv[5]))
23
24# SVG fonts are UTF-8 and each glyph's `unicode="…"` attribute IS a literal character.
25# Decoded with the platform default, a non-ASCII glyph key silently becomes the wrong
26# character (or raises) on Windows, so that glyph never matches the requested text.
27svg = open(font_path, encoding="utf-8").read()
28glyphs = {}
29for m in re.finditer(r'<glyph\s+unicode="(.)"[^>]*?horiz-adv-x="([\d.]+)"(?:[^>]*?d="([^"]*)")?', svg):
30    ch, adv, d = m.group(1), float(m.group(2)), m.group(3) or ""
31    glyphs[ch] = (adv, d)
32# default advance for space
33space_adv = glyphs.get(" ", (300, ""))[0]
34
35# total advance width in font units
36total = 0.0
37for ch in text:
38    total += glyphs.get(ch, (space_adv, ""))[0]
39s = target_w / total                       # scale font-units → px
40
41out = []
42cursor = 0.0
43NUM = re.compile(r"[-\d.]+")
44for ch in text:
45    adv, d = glyphs.get(ch, (space_adv, ""))
46    if d:
47        # polylines only (M/L): transform every coordinate pair
48        toks = re.findall(r"([ML])\s+([-\d.]+)\s+([-\d.]+)", d)
49        for cmd, xs, ys in toks:
50            x = x0 + (cursor + float(xs)) * s
51            y = baseline_y - float(ys) * s          # SVG-font y is UP; flip
52            out.append(f"{cmd} {x:.1f} {y:.1f}")
53    cursor += adv
54
55print(" ".join(out))
56print(f"[gen] chars={len(text)} scale={s:.3f} width={total*s:.0f}px "
57      f"subpaths={sum(1 for o in out if o.startswith('M'))}", file=sys.stderr)