write_transparency.rs

//! Shows three things an extended graphics state opens: half-opacity fills that
//! overlap and mix, one colour laid over another in four blend modes, and
//! overlapping letters of one text object knocked out or composited.
//!
//! 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 knockout panel sets the same line twice at half opacity, each
//! letter crossed by a stroke that overlaps it: under `TK true` the text object
//! is painted as one and the overlaps come out as light as the rest, under `TK
//! false` each glyph is composited on its own and the overlaps come out darker.
//! A reader that ignores the flag shows the two lines alike.
//!
//! The three 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, and each line with the entry its
//! state writes, which are the same in every language.
//!
//! Usage: `cargo run --example write_transparency -- tmp/transparency.pdf
//! [font.ttf]`
//!        `HQF_PDF_LANG=fr cargo run --example write_transparency --
//! tmp/transparence.pdf`

use std::env;
use std::fs;
use std::path::{Path, PathBuf};

use hqf_pdf::content::Content;
use hqf_pdf::{BlendMode, Document, ExtGState, Font, GStateHandle, Page, Rgb, TextFlow};

#[path = "shared/out.rs"]
mod out;

#[path = "shared/licence.rs"]
mod licence;

#[path = "shared/language.rs"]
mod language;

#[path = "shared/failure.rs"]
mod failure;

use language::Language;

/// The font the example draws with when none is given on the command line: the
/// one committed for the tests, so that the example runs on any machine.
fn default_font() -> PathBuf {
    Path::new(env!("CARGO_MANIFEST_DIR"))
        .join("tests")
        .join("fonts")
        .join("DejaVuSans.ttf")
}

/// The left edge the panels line up on.
const X: f64 = 80.0;

/// The line the knockout panel sets twice: each letter followed by a combining
/// stroke that takes no room of its own, so the stroke lies across the letter.
const CROSSED: &str = "O\u{338}O\u{338}O\u{338}O\u{338}";

/// The words the page is written in, one set per language.
///
/// What is not language stays out of it: each square is labelled with the name
/// the file writes for its blend mode, and each crossed line with the entry its
/// state writes.
#[derive(Debug)]
struct Words {
    /// The heading above the opacity panel.
    opacity: &'static str,
    /// The heading above the blend panel.
    blends: &'static str,
    /// The heading above the knockout panel.
    knockout: &'static str,
}

impl Words {
    /// The words the page is written in, in `language`.
    fn of(language: Language) -> &'static Self {
        language::pick(&WORDS, language)
    }
}

/// The page in English.
const ENGLISH: Words = Words {
    opacity: "Half-opacity fills overlap and mix.",
    blends: "One orange square over a blue bar, in four blend modes.",
    knockout: "Overlapping letters at half opacity: knocked out on the left, composited with one another on the right.",
};

/// The page in French.
const FRENCH: Words = 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.",
    knockout: "Des lettres qui se chevauchent, à moitié transparentes : en défonce à gauche, composées entre elles à droite.",
};

/// Every language the example is written in. A language is added by writing its
/// own set of words and naming it here.
static WORDS: [(Language, &Words); 2] =
    [(Language::English, &ENGLISH), (Language::French, &FRENCH)];

fn main() -> std::process::ExitCode {
    failure::reported(run())
}

fn run() -> Result<(), Box<dyn std::error::Error>> {
    let language = Language::from_environment()?;
    let words = Words::of(language);

    let mut args = env::args().skip(1);
    // A named file is written as named; the default one carries the language,
    // so the two languages do not overwrite each other in `tmp/`.
    let out = args
        .next()
        .unwrap_or_else(|| language.file_name(&out::default_path("transparency")));
    let font_path = args.next().map_or_else(default_font, PathBuf::from);

    let font = Font::parse(fs::read(&font_path)?)?;
    let mut doc = Document::new();
    doc.set_license(licence::licensed());
    let handle = doc.add_font(font);

    // The states the three panels apply, added once and shared.
    let half = doc.add_ext_gstate(ExtGState::new().fill_alpha(0.5));
    let modes = [
        ("Normal", BlendMode::Normal),
        ("Multiply", BlendMode::Multiply),
        ("Screen", BlendMode::Screen),
        ("Difference", BlendMode::Difference),
    ];
    let blends: Vec<(&str, GStateHandle)> = modes
        .into_iter()
        .map(|(label, mode)| (label, doc.add_ext_gstate(ExtGState::new().blend_mode(mode))))
        .collect();
    let knockouts = [
        (
            "TK true",
            doc.add_ext_gstate(ExtGState::new().fill_alpha(0.5).text_knockout(true)),
        ),
        (
            "TK false",
            doc.add_ext_gstate(ExtGState::new().fill_alpha(0.5).text_knockout(false)),
        ),
    ];

    let mut c = Content::new();

    // The opacity panel: three overlapping rectangles, each at half opacity.
    heading(&mut c, &handle, 720.0, words.opacity, X)?;
    let colors = [
        (0.0, Rgb::new(0.85, 0.15, 0.15)),
        (30.0, Rgb::new(0.15, 0.65, 0.20)),
        (60.0, Rgb::new(0.15, 0.30, 0.85)),
    ];
    for (offset, color) in colors {
        c.save_state().set_ext_gstate(&half).set_fill(color)?;
        c.rect(X + offset, 590.0, 90.0, 90.0)?.fill();
        c.restore_state();
    }

    // The blend panel: an orange square over a blue bar, once per mode.
    heading(&mut c, &handle, 520.0, words.blends, X)?;
    let square = 80.0;
    let gap = 20.0;
    let mut left = X;
    for (label, state) in &blends {
        c.set_fill(Rgb::new(0.15, 0.35, 0.80))?
            .rect(left, 380.0, square, square)?
            .fill();
        c.save_state()
            .set_ext_gstate(state)
            .set_fill(Rgb::new(0.95, 0.55, 0.10))?;
        c.rect(left + 20.0, 360.0, square, square)?.fill();
        c.restore_state();
        heading(&mut c, &handle, 350.0, label, left)?;
        left += square + gap;
    }

    // The knockout panel: the crossed line twice, the state applied before the
    // text object opens, since a text object reads the flag as it begins.
    heading(&mut c, &handle, 300.0, words.knockout, X)?;
    let crossed = TextFlow::new(&handle, 48.0).color(Rgb::new(0.15, 0.30, 0.85));
    let lines = crossed.break_lines(CROSSED, 200.0);
    let mut left = X;
    for (label, state) in &knockouts {
        c.save_state().set_ext_gstate(state);
        c.begin_text();
        crossed.draw(&mut c, &lines, left, 280.0, 200.0)?;
        c.end_text();
        c.restore_state();
        heading(&mut c, &handle, 210.0, label, left)?;
        left += 200.0;
    }

    let mut page = Page::a4();
    page.content = c.into_bytes();
    doc.add_page(page)?;

    let bytes = doc.to_bytes()?;
    if let Some(parent) = Path::new(&out).parent() {
        fs::create_dir_all(parent)?;
    }
    fs::write(&out, &bytes)?;
    println!("wrote {out}: {} bytes", bytes.len());
    Ok(())
}

/// Sets a one-line label with its baseline at `top`, left edge at `left`.
fn heading(
    c: &mut Content,
    handle: &hqf_pdf::FontHandle,
    top: f64,
    label: &str,
    left: f64,
) -> Result<(), Box<dyn std::error::Error>> {
    let flow = TextFlow::new(handle, 8.0);
    let lines = flow.break_lines(label, 400.0);
    c.begin_text();
    flow.draw(c, &lines, left, top, 400.0)?;
    c.end_text();
    Ok(())
}

#[cfg(test)]
mod tests {
    use super::{WORDS, language};

    /// The lines two languages are allowed to write the same way. There are
    /// none: every word is a word of the language it is written in.
    const SPARED: [&str; 0] = [];

    #[test]
    fn every_language_draws_the_page_in_its_own_words() {
        let untranslated = language::untranslated_lines(&WORDS, &SPARED);

        assert!(
            untranslated.is_empty(),
            "the page says these in more than one language: {untranslated:?}"
        );
    }
}