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147 | """Shows two things an extended graphics state opens: half-opacity fills that
overlap and mix, and one colour laid over another in four blend modes.
The Python twin of the `write_transparency` example in Rust. The opacity panel
draws three rectangles, each at half opacity, so the colours show through one
another where they overlap. The blend panel lays the same orange square over a
blue bar four times, once in each of four modes, so the mode each square is
painted in can be read from the colour it leaves.
The two headings are held in `Words`, once per language, and `HQF_PDF_LANG` picks which
set is drawn. Each square is labelled with the name the file writes for its blend mode,
which is the same in every language.
Usage: python examples/write_transparency.py [out.pdf] [font.ttf]
HQF_PDF_LANG=fr python examples/write_transparency.py
"""
from __future__ import annotations
from dataclasses import dataclass
from pathlib import Path
import _language
import _licence
import _out
import hqf_pdf
# The left edge the panels line up on.
X = 80.0
@dataclass(frozen=True)
class Words:
"""Every word the page draws, in one language.
What is not language stays out of it: each square is labelled with the name the file
writes for its blend mode.
"""
# The heading above the opacity panel.
opacity: str
# The heading above the blend panel.
blends: str
# The page in English.
ENGLISH = Words(
opacity="Half-opacity fills overlap and mix.",
blends="One orange square over a blue bar, in four blend modes.",
)
# The page in French.
FRENCH = Words(
opacity="Des aplats à moitié transparents se chevauchent et se mélangent.",
blends="Un carré orange sur une barre bleue, dans quatre modes de fusion.",
)
# 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 heading(
content: hqf_pdf.Content,
handle: hqf_pdf.FontHandle,
top: float,
label: str,
left: float,
) -> None:
"""Sets a one-line label with its baseline at top, left edge at left."""
flow = hqf_pdf.TextFlow(handle, 8.0)
lines = flow.break_lines(label, 400.0)
flow.draw(content, lines, left, top, 400.0)
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("transparency.pdf", language)).stem)
document = hqf_pdf.Document()
document.set_license(_licence.licensed())
handle = document.add_font(hqf_pdf.Font.from_path(_out.font_path()))
# The states the two panels apply, added once and shared.
half = document.add_ext_gstate(hqf_pdf.ExtGState(fill_alpha=0.5))
modes = (
("Normal", hqf_pdf.BlendMode.Normal),
("Multiply", hqf_pdf.BlendMode.Multiply),
("Screen", hqf_pdf.BlendMode.Screen),
("Difference", hqf_pdf.BlendMode.Difference),
)
blends = [
(label, document.add_ext_gstate(hqf_pdf.ExtGState(blend_mode=mode)))
for label, mode in modes
]
content = hqf_pdf.Content()
# The opacity panel: three overlapping rectangles, each at half opacity.
heading(content, handle, 720.0, words.opacity, X)
colors = (
(0.0, hqf_pdf.Rgb(0.85, 0.15, 0.15)),
(30.0, hqf_pdf.Rgb(0.15, 0.65, 0.20)),
(60.0, hqf_pdf.Rgb(0.15, 0.30, 0.85)),
)
for offset, color in colors:
content.save_state()
content.set_ext_gstate(half)
content.set_fill(color)
content.rect(X + offset, 590.0, 90.0, 90.0)
content.fill()
content.restore_state()
# The blend panel: an orange square over a blue bar, once per mode.
heading(content, handle, 520.0, words.blends, X)
square = 80.0
gap = 20.0
left = X
for label, state in blends:
content.set_fill(hqf_pdf.Rgb(0.15, 0.35, 0.80))
content.rect(left, 380.0, square, square)
content.fill()
content.save_state()
content.set_ext_gstate(state)
content.set_fill(hqf_pdf.Rgb(0.95, 0.55, 0.10))
content.rect(left + 20.0, 360.0, square, square)
content.fill()
content.restore_state()
heading(content, handle, 350.0, label, left)
left += square + gap
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()
|