Textes et formes remplis d'un dégradé

//! Fills text and a shape with a gradient, through a shading pattern.
//!
//! Where `write_gradient` paints a gradient into a clipped box, this makes a
//! gradient the colour something is *filled* with: a headline whose letters are
//! windows onto a three-stop blend, and a panel filled with a radial one. The
//! gradient lives in the page's own space, so the letters show the part of it
//! behind them.
//!
//! The two captions are held in `Words`, once per language, and `HQF_PDF_LANG`
//! picks which set is drawn. The headline is the library's own name and reads
//! the same in every language.
//!
//! Usage: `cargo run --example write_gradient_fill -- tmp/gradient_fill.pdf
//! [font.ttf]`
//!        `HQF_PDF_LANG=fr cargo run --example write_gradient_fill --
//! tmp/degrade_remplissage.pdf`

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

use hqf_pdf::content::Content;
use hqf_pdf::{
    Axial, DeviceSpace, Document, Exponential, Font, FontHandle, Page, Radial, Rgb, Shading,
    Stitching,
};

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

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

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

use language::Language;

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

/// The headline the gradient fills, which is the library's own name.
const HEADLINE: &str = "hqf-pdf";

/// The words the page is written in, one set per language.
#[derive(Debug)]
struct Words {
    /// The caption under the headline.
    letters: &'static str,
    /// The caption under the panel.
    shape: &'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 {
    letters: "Text filled with a gradient, through a shading pattern.",
    shape: "A shape filled with a radial gradient.",
};

/// The page in French.
const FRENCH: Words = Words {
    letters: "Du texte rempli par un dégradé, au moyen d'un motif.",
    shape: "Une forme remplie par un dégradé en cercle.",
};

/// 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)];

/// Draws one line of text with its baseline at `(x, y)`, in whatever fill
/// colour is in force.
fn text(
    content: &mut Content,
    font: &FontHandle,
    size: f64,
    x: f64,
    y: f64,
    line: &str,
) -> Result<(), hqf_pdf::Error> {
    content.begin_text();
    content.set_font(font.name(), size)?;
    content.text_origin(x, y)?;
    content.show_glyphs(&font.glyphs(line));
    content.end_text();
    Ok(())
}

fn main() -> 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("gradient_fill")));
    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);

    let left = 70.0;

    // A three-stop gradient spanning the width of the headline, set as a fill
    // pattern so the letters show it through their shapes.
    let headline_size = 84.0;
    let headline_baseline = 660.0;
    let headline_width = handle.measure(HEADLINE, headline_size);
    let ramp = Stitching::new(
        [0.0, 1.0],
        vec![
            Exponential::new([0.0, 1.0], 1.0)
                .endpoints(vec![0.85, 0.12, 0.12], vec![0.12, 0.55, 0.2])
                .into(),
            Exponential::new([0.0, 1.0], 1.0)
                .endpoints(vec![0.12, 0.55, 0.2], vec![0.12, 0.2, 0.8])
                .into(),
        ],
        vec![0.5],
        vec![[0.0, 1.0], [0.0, 1.0]],
    );
    let letters = doc.add_shading_pattern(&Shading::from(Axial::new(
        (left, headline_baseline),
        (left + headline_width, headline_baseline),
        DeviceSpace::Rgb,
        ramp,
    )))?;

    // A radial gradient filling a panel below the headline.
    let (px, py, pw, ph) = (left, 350.0, 455.0, 190.0);
    let panel = doc.add_shading_pattern(&Shading::from(
        Radial::rgb(
            (px + pw / 2.0, py + ph / 2.0, 0.0),
            (px + pw / 2.0, py + ph / 2.0, pw / 2.0),
            Rgb::new(1.0, 1.0, 1.0),
            Rgb::new(0.1, 0.15, 0.45),
        )
        .extend(false, true),
    ))?;

    let mut content = Content::new();

    // The headline, its letters filled with the gradient.
    content.save_state();
    content.set_fill_pattern(&letters);
    text(
        &mut content,
        &handle,
        headline_size,
        left,
        headline_baseline,
        HEADLINE,
    )?;
    content.restore_state();

    // A caption, in plain black.
    text(
        &mut content,
        &handle,
        13.0,
        left,
        headline_baseline - 26.0,
        words.letters,
    )?;

    // The panel, filled with the radial gradient.
    content.save_state();
    content.set_fill_pattern(&panel);
    content.rect(px, py, pw, ph)?.fill();
    content.restore_state();

    text(&mut content, &handle, 12.0, px, py - 16.0, words.shape)?;

    let mut page = Page::a4();
    page.content = content.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(())
}

#[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:?}"
        );
    }
}