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152 | """Writes a page of QR codes, drawn as squares.
The Python twin of the `write_qr` example in Rust: the same page, through the
binding rather than through the library directly.
Whether a QR code works is not a question the page can answer, and not one a human
eye can: it is answered by a scanner. So the page carries what each code says
under it, and `scripts/check_qr.sh` points a decoder at the rendered image and
compares.
The head of the sheet says what the squares are for, so that the page is worth
something to whoever opens it without the code beside it. Those words are held in
`Words`, once per language, and `HQF_PDF_LANG` picks which set the sheet is headed in.
What the codes carry stands apart from them: a scanner reads it, not a person, and it is
the same in every language.
Usage: python examples/write_qr.py [out.pdf] [font.ttf]
HQF_PDF_LANG=fr python examples/write_qr.py
"""
from __future__ import annotations
from dataclasses import dataclass
from pathlib import Path
import _language
import _licence
import _out
import hqf_pdf
# What the codes carry: an invoice link, a payment reference, and a line of mixed
# punctuation.
CARRIED = [
"https://example.test/invoice/FR-1964413",
"REF 2026-07-16/ACME",
"a-Z 0..9 +*#% and on",
]
# The side of one module, in points. Four pixels to a module at 288dpi, so every
# module's edge lands on a pixel boundary.
MODULE = 3.0
# Where the foot of the row of codes sits, in points up from the foot of the sheet.
TOP = 640.0
# How far in from the left edge of the sheet the head of the page is set. The quiet zone
# of the first code starts here too, so the heading stands over the left edge of the row
# of codes.
MARGIN = 72.0
# Where the baseline of the heading sits, in points up from the foot of the sheet.
HEAD_TOP = 794.0
# The size the heading is set at, in points.
HEADING = 16.0
# The size the lines under the heading are set at, in points.
BODY = 10.5
# How far under the heading the first line beneath it sits, in points.
HEAD_GAP = 24.0
# How far below one line under the heading the next one sits, in points.
LINE_STEP = 15.0
@dataclass(frozen=True)
class Words:
"""Every word the sheet is headed in, in one language."""
# What the page says it is, at its head and in what the file says of itself.
title: str
# What the page says under its heading.
lines: tuple[str, str]
# The head of the sheet in English.
ENGLISH = Words(
title="QR codes, drawn as squares",
lines=(
"A QR code holds a link or a reference that a telephone reads in one shot. It is",
"drawn square by square here, so it stays readable at any size it is printed at.",
),
)
# The head of the sheet in French.
FRENCH = Words(
title="Des codes QR, dessinés en carrés",
lines=(
"Un code QR porte un lien ou une référence qu'un téléphone lit d'un seul coup. Il",
"est dessiné carré par carré ici, donc il reste lisible à toute taille imprimée.",
),
)
# Every language the example is written in. A language is added by writing its own set
# of words and naming it here.
WORDS = {_language.ENGLISH: ENGLISH, _language.FRENCH: FRENCH}
def head(content, handle, words) -> None:
"""Draw the heading, and the lines under it that say what the page is for."""
content.draw_text(handle, HEADING, MARGIN, HEAD_TOP, words.title)
y = HEAD_TOP - HEAD_GAP
for line in words.lines:
content.draw_text(handle, BODY, MARGIN, y, line)
y -= LINE_STEP
def main() -> None:
language = _language.from_environment()
words = _language.words_of(WORDS, language)
# A named file is written as named; the default one carries the language, so the two
# languages do not overwrite each other in `tmp/`.
out = _out.output_path(Path(_language.file_name("qr.pdf", language)).stem)
document = hqf_pdf.Document()
document.set_license(_licence.licensed())
document.set_info("Title", words.title)
handle = document.add_font(hqf_pdf.Font.from_path(_out.font_path()))
content = hqf_pdf.Content()
content.set_fill(hqf_pdf.Rgb(0.0, 0.0, 0.0))
head(content, handle, words)
quiet = hqf_pdf.QrCode.quiet_zone() * MODULE
left = MARGIN
top = TOP
for carried in CARRIED:
code = hqf_pdf.QrCode(carried)
side = code.size * MODULE
caption = handle.measure(carried, 8.0)
# The quiet zone is the caller's: the code is drawn that far in, and nothing
# else is drawn beside it.
content.draw_qr(code, left + quiet, top, side)
content.draw_text(handle, 8.0, left + quiet, top - 12.0, carried)
left += max(side, caption) + quiet * 2.0 + 24.0
page = hqf_pdf.Page.a4()
page.set_content(content)
document.add_page(page)
written = document.write(out)
print(f"wrote {out} ({written} bytes)")
if __name__ == "__main__":
main()
|