docs: new design for the documentation site

Apply the brand to the Material for MkDocs site: Inter and JetBrains Mono
served by the site (upright and real italic), brand colours, blue header band
with the syntax pattern, wordmark in the header, new home page (hero, cards,
animated feature tour), 404 page, polish for tabs, search, footer, focus
rings, tables and code blocks, and theme features (code copy, previous/next
footer, TOC follow, search suggestions).

Draw the number railroad diagram, the parser callback events and the iterator
illustrations as inline SVGs that follow the light and dark scheme. The
generator scripts are in docs/mkdocs/scripts/figures; the feature slideshow
(json-light.svg, json-dark.svg, replacing json.gif on the home page) is built
by docs/mkdocs/scripts/slideshow. Decision nodes in five flowcharts become
hexagons, which need far less room.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
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Niels Lohmann committed 2026-10-25 20:40:26 +01:00
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#!/usr/bin/env -S uv run --script
# /// script
# requires-python = ">=3.9"
# dependencies = ["fonttools==4.67.0", "uharfbuzz==0.57.0"]
# ///
"""Animated SVG slideshow prototype for nlohmann/json, all text outlined (harfbuzz shaping, glyphs as <path> + <use>).
Usage: uv run --script build.py OUT.svg [seconds-per-slide] [auto|light|dark]
auto (the default) follows prefers-color-scheme. light and dark fix the colours, for pages with their own theme
toggle (MkDocs Material), which an <img> cannot see.
The pinned versions keep the output byte-identical; a different harfbuzz may shape slightly differently.
"""
import re, sys, os
import uharfbuzz as hb
from fontTools.pens.svgPathPen import SVGPathPen
HERE = os.path.dirname(os.path.abspath(__file__))
FONTS = os.path.join(HERE, "fonts")
W, H = 1200, 675
TOTAL = 0 # number of slides, set once slides.md is read (for the "02 / 20" labels and the progress segments)
# ---------------------------------------------------------------- glyphs
class Face:
def __init__(self, file, key, feats=None):
blob = hb.Blob.from_file_path(os.path.join(FONTS, file))
self.face = hb.Face(blob)
self.upem = self.face.upem
self.key = key
self.feats = feats or {}
def font(self, var):
f = hb.Font(self.face)
f.set_variations(var)
return f
INTER = Face("Inter.ttf", "i", {"cv11": True, "ss03": True, "kern": True})
MONO = Face("JetBrainsMono.ttf", "m", {"calt": False, "liga": False})
GLYPHS = {} # (face, var, gid) -> id
DEFS = []
def gid_ref(face, font, var, gid):
k = (face.key, tuple(sorted(var.items())), gid)
if k not in GLYPHS:
pen = SVGPathPen(None, ntos=lambda v: str(round(v)))
font.draw_glyph_with_pen(gid, pen)
d = pen.getCommands()
gidname = f"g{len(GLYPHS):x}"
GLYPHS[k] = gidname if d else None
if d:
DEFS.append(f'<path id="{gidname}" d="{d}"/>')
return GLYPHS[k]
def shape(face, text, wght, size, track=0.0):
if not text:
return [], 0, face.upem
var = {"wght": wght}
if face is INTER:
var["opsz"] = max(14, min(32, size))
font = face.font(var)
buf = hb.Buffer()
buf.add_str(text)
buf.guess_segment_properties()
hb.shape(font, buf, face.feats)
out, x = [], 0
tr = track * face.upem
for info, pos in zip(buf.glyph_infos, buf.glyph_positions):
out.append((gid_ref(face, font, var, info.codepoint), x + pos.x_offset, pos.y_offset))
x += pos.x_advance + tr
return out, x - tr, face.upem
def width(text, face=INTER, wght=400, size=16, track=0.0):
_, w, upem = shape(face, text, wght, size, track)
return w * size / upem
def run(text, x, y, size, wght=400, cls="tx", face=INTER, track=0.0):
"""One line of text, baseline at y. Returns (svg, width_px)."""
glyphs, w, upem = shape(face, text, wght, size, track)
s = size / upem
uses = "".join(f'<use href="#{g}" x="{gx}"' + (f' y="{-gy}"' if gy else "") + "/>"
for g, gx, gy in glyphs if g)
return (f'<g class="{cls}" transform="translate({x:g} {y:g}) scale({s:.6g} {-s:.6g})">{uses}</g>', w * s)
def runs(parts, x, y, size, face=INTER, track=0.0):
"""Several (text, wght, cls) pieces on one line."""
out = []
for text, wght, cls in parts:
svg, w = run(text, x, y, size, wght, cls, face, track)
out.append(svg)
x += w + track * size
return "".join(out), x
def wrap(text, maxw, size, wght=400):
lines = _wrap(text, maxw, size, wght)
# no one-word widow: pull the last word of the previous line down if it still fits
if len(lines) > 1 and " " not in lines[-1] and " " in lines[-2]:
head, last = lines[-2].rsplit(" ", 1)
if width(last + " " + lines[-1], size=size, wght=wght) <= maxw:
lines[-2:] = [head, last + " " + lines[-1]]
return lines
def _wrap(text, maxw, size, wght=400):
lines, cur = [], ""
for word in text.split(" "):
t = (cur + " " + word).strip()
if cur and width(t, size=size, wght=wght) > maxw:
lines.append(cur)
cur = word
else:
cur = t
return lines + [cur]
# ---------------------------------------------------------------- pieces
def wordmark(x, y, size, on="page"):
"""The wordmark with hand kerning around the slash (see the logo in the brand kit). Below 32 px it switches to the
small optical master (nlohmann 250 / slash 450), because Thin falls apart at footer size."""
a, sl = ("wm-a", "wm-s") if on == "page" else ("on-a", "on-s")
small = size < 32
w = (250, 450, 800) if small else (100, 400, 800)
k = (0.004, 0.024) if small else (-0.006, 0.012)
out = []
for i, (t, wg, c) in enumerate([("nlohmann", w[0], a), ("/", w[1], sl), ("json", w[2], a)]):
svg, wd = run(t, x, y, size, wg, c, track=-0.02)
out.append(svg)
x += wd - 0.02 * size + (k[i] * size if i < 2 else 0)
return "".join(out), x
KW = {"using", "auto", "return", "const", "struct", "for", "override"}
TYPES = {"int", "void", "bool", "double", "char", "float"}
CONSTANTS = {"true", "false", "nullptr"}
TOKEN = re.compile(r'(//.*$)|(R"\(.*?\)"|R"\(.*$|"(?:[^"\\]|\\.)*"|\'(?:[^\'\\]|\\.)\')|(<[\w/.]+>(?=\s*$))|(#\w+)'
r'|(\b\d+(?:\.\d+)?\b)|(\b[A-Za-z_]\w*\b)|(\s+)|(.)')
def code_block(lines, x, y, size, lh):
"""Lines of C++; a raw string literal may span lines."""
out, in_raw = [], False
for line in lines:
if line:
svg, in_raw = code_line(line, x, y, size, in_raw)
out.append(svg)
y += lh
else:
y += lh * BLANK
return "".join(out)
BLANK = 0.55 # an empty code line is a paragraph break, not a full line
def code_height(lines, size, lh):
n_full = sum(1 for l in lines if l)
n_blank = len(lines) - n_full
return lh * (n_full - 1) + lh * BLANK * n_blank + size
def code_line(line, x, y, size, in_raw=False):
if line.startswith("$ "):
return runs([("$ ", 400, "tx3"), (line[2:], 400, "tx")], x, y, size, MONO)[0], False
out, cx = [], x
if in_raw:
end = line.find(')"')
head = line if end < 0 else line[:end + 2]
svg, w = run(head, cx, y, size, 400, "str", MONO)
out.append(svg)
if end < 0:
return "".join(out), True
cx += w
line = line[end + 2:]
in_raw = False
for m in TOKEN.finditer(line):
com, st, inc, pp, num, ident, ws, other = m.groups()
t = m.group(0)
if st and st.startswith('R"(') and not st.endswith(')"'):
in_raw = True
face, wght, cls = MONO, 400, "tx"
if com:
cls = "com" # upright: JetBrains Mono Italic's cursive f reads as a florin at README size
elif st or inc:
cls = "str"
elif pp:
cls = "pp"
elif ident in KW:
wght, cls = 600, "kw"
elif ident in TYPES:
cls = "ty"
elif num or ident in CONSTANTS:
cls = "num"
elif ident and line[m.end():m.end() + 1] == "(":
cls = "fn" # a call or definition: name directly followed by "("
svg, w = run(t, cx, y, size, wght, cls, face)
if not ws:
out.append(svg)
cx += w
return "".join(out), in_raw
SEG, SEG_GAP = 20, 5
def progress(idx, n_proto, y):
"""TOTAL segments at the bottom right; earlier slides full, current one fills over the slide's time."""
seg, gap = SEG, SEG_GAP
x0 = W - 64 - TOTAL * seg - (TOTAL - 1) * gap
out = []
for k in range(TOTAL):
x = x0 + k * (seg + gap)
out.append(f'<rect class="seg" x="{x}" y="{y}" width="{seg}" height="3" rx="1.5"/>')
if k < idx:
out.append(f'<rect class="seg-on" x="{x}" y="{y}" width="{seg}" height="3" rx="1.5"/>')
elif k == idx:
out.append(f'<rect class="seg-on fill" x="{x}" y="{y}" width="{seg}" height="3" rx="1.5"/>')
return "".join(out)
def pattern_def():
tile = [("{", 14, 34), ("]", 92, 22), (":", 136, 60), ("[", 52, 82), (",", 118, 112),
("}", 20, 140), (":", 78, 150), ("{", 140, 158)]
glyphs = "".join(run(c, x, y, 26, 600, "pat", MONO)[0] for c, x, y in tile)
return f'<pattern id="pat" width="160" height="160" patternUnits="userSpaceOnUse">{glyphs}</pattern>'
# ---------------------------------------------------------------- slides
CODE_SIZES = []
SLOGAN = "What if JSON was part of modern C++?"
def band_bg():
"""Hero gradient plus the syntax pattern, faded out towards the text side (left)."""
return ('<rect width="1200" height="675" fill="url(#hero)"/>'
'<rect width="1200" height="675" fill="url(#pat)" mask="url(#patfade)"/>')
def footer_band(idx, n, left=None):
out = []
if left:
out.append(run(left, 64, FOOT_Y, 20, 600, "on-tx")[0])
out.append(progress(idx, n, FOOT_Y - 7.5).replace('class="seg"', 'class="seg on-band"').replace('class="seg-on', 'class="seg-on on-band'))
return "".join(out)
FOOT_Y = 640 # one footer baseline on every slide: wordmark or URL left, progress right
def slide_title(idx, n):
out = [band_bg()]
x = 96
label = "VERSION 3.13.0"
lw = width(label, MONO, 500, 15, 0.04)
out.append(f'<rect class="chip" x="{x}" y="186" width="{lw + 28:.1f}" height="34" rx="4"/>')
out.append(run(label, x + 14, 208.5, 15, 500, "on-tx", MONO, 0.04)[0])
out.append(wordmark(x - 6, 336, 112, on="band")[0])
out.append(runs([("// ", 400, "w70"), (SLOGAN, 400, "on-s")], x, 404, 26, MONO)[0])
out.append(footer_band(idx, n, "github.com/nlohmann/json"))
return "".join(out)
def slide_feature(idx, n, title, bullets, code, badge=None):
out = ['<rect class="bg" width="1200" height="675"/>']
x, top, bottom = 64, 136, 596
# title row: 48/800, -3 %
svg, tw = run(title, x - 2, 98, 48, 800, "tx", track=-0.03)
out.append(svg)
if badge:
cx = x + tw + 16
cw = width(badge, MONO, 600, 13, 0.06) + 18
out.append(f'<rect class="red" x="{cx:.1f}" y="68.5" width="{cw:.1f}" height="26" rx="4"/>')
out.append(run(badge, cx + 9, 86.2, 13, 600, "on-tx", MONO, 0.06)[0])
# code panel: fixed left edge, fixed width, fixed top on every slide; only its height follows the code
pad, lf = 28, 1.45
px, pw = 488, 1136 - 488
em = max(width(l, MONO, 400, 1) for l in code)
cs = 19.0
while cs > 14 and (em * cs > pw - 2 * pad or code_height(code, cs, lf * cs) > bottom - top - 2 * pad):
cs -= 0.5
CODE_SIZES.append((title, cs))
if cs < 18:
print(f" warning: {title!r} code at {cs} px ({em * 19:.0f} px wide at 19 px)", file=sys.stderr)
lh = lf * cs
ph = max(2 * pad + code_height(code, cs, lh), 240)
out.append(f'<rect class="panel" x="{px}" y="{top}" width="{pw}" height="{ph:.0f}" rx="6"/>')
first = top + pad + cs * 0.78
out.append(code_block(code, px + pad, first, cs, lh))
# bullets: 24/400 on 34, first baseline level with the first code baseline
colw = px - x - 40
by = first
for b in bullets:
out.append(f'<rect class="blk" x="{x}" y="{by - 10.6:.1f}" width="8" height="8" rx="1.5"/>')
for line in wrap(b, colw - 24, 24):
out.append(run(line, x + 24, by, 24, 400, "tx2")[0])
by += 34
by += 16
# footer: small-master wordmark left, progress right, no rule, no numeral
out.append(wordmark(64, FOOT_Y, 22)[0])
out.append(progress(idx, n, FOOT_Y - 7.5))
return "".join(out)
def slide_closing(idx, n):
out = [band_bg()]
x = 96
out.append(wordmark(x - 4, 146, 80, on="band")[0])
out.append(runs([("// ", 400, "w70"), (SLOGAN, 400, "on-s")], x, 200, 22, MONO)[0])
info = [
("{", None),
(' "copyright": ', "(c) 2013-2026 Niels Lohmann"),
(' "license": ', "MIT"),
(' "docs": ', "json.nlohmann.me"),
(' "github": ', "github.com/nlohmann/json"),
(' "sponsor": ', "github.com/sponsors/nlohmann"),
(' "mail": ', "mail@nlohmann.me"),
("}", None),
]
cs, lh, pad = 21, 33, 28
py = 244
pw = max(width(k + '"' + (v or "") + '",', MONO, 400, cs) for k, v in info) + 2 * pad
out.append(f'<rect class="on-panel" x="{x}" y="{py}" width="{pw:.0f}" height="{2 * pad + lh * (len(info) - 1) + cs:.0f}" rx="6"/>')
y = py + pad + cs * 0.8
for k, (key, val) in enumerate(info):
if val is None:
out.append(run(key, x + pad, y, cs, 400, "on-tx", MONO)[0])
else:
comma = "," if k < len(info) - 2 else ""
out.append(runs([(key, 400, "on-tx"), (f'"{val}"', 400, "on-s"), (comma, 400, "on-tx")], x + pad, y, cs, MONO)[0])
y += lh
out.append(footer_band(idx, n))
return "".join(out)
def load_slides(path):
"""Feature slides from Markdown: '# Title {badge: TEXT}', '- bullet' lines, one fenced code block."""
text = re.sub(r"<!--.*?-->", "", open(path).read(), flags=re.S)
slides, cur, in_code = [], None, False
for no, line in enumerate(text.split("\n"), 1):
if in_code:
if line.startswith("```"):
in_code = False
else:
cur["code"].append(line)
elif line.startswith("```"):
in_code = True
elif line.startswith("# "):
title, badge = line[2:].strip(), None
m = re.search(r"\s*\{badge:\s*(.*?)\}$", title)
if m:
title, badge = title[:m.start()], m.group(1)
cur = {"title": title, "bullets": [], "code": [], "badge": badge}
slides.append(cur)
elif line.startswith("- ") and cur:
cur["bullets"].append(line[2:].strip())
elif line[:1] in " \t" and line.strip() and cur and cur["bullets"]:
cur["bullets"][-1] += " " + line.strip()
elif line.strip():
raise SystemExit(f"{path}:{no}: unexpected line: {line!r}")
for sl in slides:
while sl["code"] and not sl["code"][-1].strip():
sl["code"].pop()
if not sl["code"]:
raise SystemExit(f"{path}: slide {sl['title']!r} has no code block")
return slides
FEATURES = load_slides(os.path.join(HERE, "slides.md"))
def _feature(f):
return lambda i, n: slide_feature(i, n, f["title"], f["bullets"], f["code"], f["badge"])
SLIDES = [slide_title] + [_feature(f) for f in FEATURES] + [slide_closing]
TOTAL = len(SLIDES)
# ---------------------------------------------------------------- assemble
def build(sec):
n = len(SLIDES)
T = n * sec
fade = 0.6
a, b, c = fade / T * 100, sec / T * 100, (sec + fade) / T * 100
def cls(i):
return "s s0" if i == 0 else "s sl" if i == n - 1 else "s"
bodies = [f'<g class="{cls(i)}" style="animation-delay:{i * sec:g}s">{fn(i, n)}</g>' for i, fn in enumerate(SLIDES)]
css = f"""
.bg{{fill:#fff}} .tx{{fill:#0f1419}} .tx2{{fill:#3d444f}} .tx3{{fill:#8a919c}} .com{{fill:#646d7a}}
.bl{{fill:#1747a6}} .blk{{fill:#1747a6}} .kw{{fill:#1747a6}} .ty{{fill:#0d6e72}} .fn{{fill:#6b3fb8}} .str{{fill:#23793a}} .num{{fill:#b04a07}} .pp{{fill:#a3247a}}
.panel{{fill:#f5f7fa;stroke:#e3e6eb;stroke-width:1}} .rule{{stroke:#e3e6eb;stroke-width:1}}
.wm-a{{fill:#0f1419}} .wm-s{{fill:#1747a6}}
.on-a,.on-tx{{fill:#fff}} .red{{fill:#d93a3f}} .on-panel{{fill:#fff;fill-opacity:.08;stroke:#fff;stroke-opacity:.16}} .on-s{{fill:#bcd3fb}} .w70{{fill:#fff;fill-opacity:.7}} .on-tx2{{fill:#dbe6fb}} .chip{{fill:#fff;fill-opacity:.14}}
.pat{{fill:#fff;fill-opacity:.09}}
.h1{{stop-color:#1d55c4}} .h2{{stop-color:#123a8a}}
.seg{{fill:#e3e6eb}} .seg-on{{fill:#1747a6}}
.seg.on-band{{fill:#fff;fill-opacity:.25}} .seg-on.on-band{{fill:#fff;fill-opacity:1}}
@media (prefers-color-scheme:dark){{
.bg{{fill:#0f1218}} .tx,.wm-a{{fill:#f2f4f7}} .tx2{{fill:#c3c8d1}} .tx3{{fill:#7b828e}} .com{{fill:#8b929e}}
.bl,.blk,.wm-s,.seg-on,.kw{{fill:#7aa7f5}} .ty{{fill:#4fd1c5}} .fn{{fill:#c4a3ff}} .str{{fill:#7ed491}} .num{{fill:#f5a65b}} .pp{{fill:#f48fc8}}
.panel{{fill:#171b23;stroke:#272c36}} .rule{{stroke:#272c36}} .seg{{fill:#272c36}}
.red{{fill:#c8383d}} .h1{{stop-color:#163f93}} .h2{{stop-color:#0c2556}}
}}
.s{{opacity:0;animation:show {T:g}s linear infinite backwards}}
.fill{{transform-box:fill-box;transform-origin:left;animation:fill {T:g}s linear infinite backwards;animation-delay:inherit}}
.s0{{animation-name:show0}} .sl{{animation-name:showl}}
@keyframes show{{0%{{opacity:0;animation-timing-function:cubic-bezier(.2,.6,.2,1)}} {a:.4f}%{{opacity:1}} {c:.4f}%{{opacity:1}} {c + .01:.4f}%{{opacity:0}} 100%{{opacity:0}}}}
@keyframes show0{{0%{{opacity:1}} {c:.4f}%{{opacity:1}} {c + .01:.4f}%{{opacity:0}} 100%{{opacity:0}}}}
@keyframes showl{{0%{{opacity:0;animation-timing-function:cubic-bezier(.2,.6,.2,1)}} {a:.4f}%{{opacity:1}} {b:.4f}%{{opacity:1}} {c:.4f}%{{opacity:0}} 100%{{opacity:0}}}}
@keyframes fill{{0%{{transform:scaleX(0)}} {b:.4f}%{{transform:scaleX(1)}} 100%{{transform:scaleX(1)}}}}
@media (prefers-reduced-motion:reduce){{.s,.fill{{animation:none}} .s:first-of-type{{opacity:1}}}}
"""
css = re.sub(r"\n\s*", "", css)
pat = pattern_def()
return (f'<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 {W} {H}" width="{W}" height="{H}" role="img">'
f'<title>JSON for Modern C++: feature slideshow (animated, {n} slides, {sec:g} s each)</title>'
f'<style>{css}</style>'
f'<defs>{"".join(DEFS)}{pat}'
f'<linearGradient id="hero" gradientTransform="rotate(70 .5 .5)"><stop class="h1" offset="0"/><stop class="h2" offset="1"/></linearGradient>'
f'<linearGradient id="fadeg" x1="0" x2="1" y1="0" y2="0"><stop offset=".25" stop-color="#fff" stop-opacity="0"/><stop offset=".85" stop-color="#fff" stop-opacity="1"/></linearGradient>'
f'<mask id="patfade" maskUnits="userSpaceOnUse" x="0" y="0" width="{W}" height="{H}"><rect width="{W}" height="{H}" fill="url(#fadeg)"/></mask></defs>'
f'<rect class="bg" width="{W}" height="{H}"/>'
f'{"".join(bodies)}</svg>')
def fix_scheme(svg, scheme):
"""Drop the dark-mode block (light) or apply it unconditionally (dark)."""
if scheme == "auto":
return svg
start = svg.index("@media (prefers-color-scheme:dark){")
i, depth = svg.index("{", start), 0
for j in range(i, len(svg)):
depth += {"{": 1, "}": -1}.get(svg[j], 0)
if depth == 0:
break
inner = svg[i + 1:j] if scheme == "dark" else ""
return svg[:start] + inner + svg[j + 1:]
if __name__ == "__main__":
out = sys.argv[1]
sec = float(sys.argv[2]) if len(sys.argv) > 2 else 15
scheme = sys.argv[3] if len(sys.argv) > 3 else "auto"
if scheme not in ("auto", "light", "dark"):
sys.exit(f"unknown colour scheme {scheme!r}: use auto, light or dark")
svg = fix_scheme(build(sec), scheme)
# defs are appended while slides render, so build the slides first (done inside build via f-string order)
open(out, "w").write(svg)
print(out, len(svg.encode()) // 1024, "KB,", len(GLYPHS), "glyphs; code px:", " ".join(f"{c:g}" for _, c in CODE_SIZES))