example code for dwrote-rs to exercise fallback

fallback.rs

extern crate dwrote;
extern crate winapi;

use std::borrow::Cow;
use winapi::um::dwrite::{DWRITE_NUMBER_SUBSTITUTION_METHOD_NONE, DWRITE_READING_DIRECTION,
    DWRITE_READING_DIRECTION_LEFT_TO_RIGHT
};

use dwrote::{FontCollection, FontFallback, FontStretch, FontStyle, FontWeight, NumberSubstitution,
    TextAnalysisSource, TextAnalysisSourceImpl,
};

struct MyTextAnalysisSource(u32);

impl TextAnalysisSourceImpl for MyTextAnalysisSource {
    fn get_locale_name<'a>(&'a self, text_pos: u32) -> (Cow<'a, str>, u32) {
        ("en-US".into(), self.0 - text_pos)
    }

    fn get_paragraph_reading_direction(&self) -> DWRITE_READING_DIRECTION {
        DWRITE_READING_DIRECTION_LEFT_TO_RIGHT
    }
}

fn main() {
    let collection = FontCollection::get_system(true);
    let count = collection.get_font_family_count();
    println!("system font: {} families", count);
    /*
    for i in 0..count {
        let family = collection.get_font_family(i);
        println!("font {}: {}", i, family.name());
    }
    */
    let fallback = FontFallback::get_system_fallback().expect("error getting fallback");
    let text = "\u{4000}";
    let text: Vec<_> = text.encode_utf16().collect();
    println!("text: {:x?}", text);
    let number_subst = NumberSubstitution::new(
        DWRITE_NUMBER_SUBSTITUTION_METHOD_NONE,
        "en-US",
        true,
    );
    let len = text.len();
    let text_analysis = TextAnalysisSource::new(
        Box::new(MyTextAnalysisSource(text.len() as u32)),
        text,
        number_subst,
    );
    let fallback_result = fallback.map_characters(
        &text_analysis,
        0,
        len as u32,
        &collection,
        Some("Arial"),
        FontWeight::Regular,
        FontStyle::Normal,
        FontStretch::Normal,
    );
    println!("fallback result: {}, {:?}, {}",
        fallback_result.mapped_length,
        fallback_result.mapped_font.map(|f| f.family_name()),
        fallback_result.scale
    );
}