qrcode 0.14.1

QR code encoder in Rust
Documentation 
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//! UTF-8 rendering, with 2 pixels per symbol.

use crate::render::{Canvas as RenderCanvas, Color, Pixel};

const CODEPAGE: [&str; 4] = [" ", "\u{2584}", "\u{2580}", "\u{2588}"];

#[derive(Copy, Clone, PartialEq)]
pub enum Dense1x2 {
    Dark,
    Light,
}

impl Pixel for Dense1x2 {
    type Image = String;
    type Canvas = Canvas1x2;
    fn default_color(color: Color) -> Dense1x2 {
        color.select(Dense1x2::Dark, Dense1x2::Light)
    }
    fn default_unit_size() -> (u32, u32) {
        (1, 1)
    }
}

impl Dense1x2 {
    fn value(self) -> u8 {
        match self {
            Dense1x2::Dark => 1,
            Dense1x2::Light => 0,
        }
    }
    fn parse_2_bits(sym: u8) -> &'static str {
        CODEPAGE[usize::from(sym)]
    }
}

pub struct Canvas1x2 {
    canvas: Vec<u8>,
    width: u32,
    dark_pixel: u8,
}

impl RenderCanvas for Canvas1x2 {
    type Pixel = Dense1x2;
    type Image = String;

    fn new(width: u32, height: u32, dark_pixel: Dense1x2, light_pixel: Dense1x2) -> Self {
        let a = vec![light_pixel.value(); (width * height) as usize];
        Canvas1x2 { width, canvas: a, dark_pixel: dark_pixel.value() }
    }

    fn draw_dark_pixel(&mut self, x: u32, y: u32) {
        self.canvas[(x + y * self.width) as usize] = self.dark_pixel;
    }

    fn into_image(self) -> String {
        self.canvas
            // Chopping array into 1-line sized fragments
            .chunks_exact(self.width as usize)
            .collect::<Vec<&[u8]>>()
            // And then glueing every 2 lines.
            .chunks(2)
            .map(|rows| {
                {
                    // Then zipping those 2 lines together into a single 2-bit number list.
                    if rows.len() == 2 {
                        rows[0].iter().zip(rows[1]).map(|(top, bot)| (top * 2 + bot)).collect::<Vec<u8>>()
                    } else {
                        rows[0].iter().map(|top| (top * 2)).collect::<Vec<u8>>()
                    }
                }
                .into_iter()
                // Mapping those 2-bit numbers to corresponding pixels.
                .map(Dense1x2::parse_2_bits)
                .collect::<Vec<&str>>()
                .concat()
            })
            .collect::<Vec<String>>()
            .join("\n")
    }
}

#[test]
fn test_render_to_utf8_string() {
    use crate::render::Renderer;
    let colors = &[Color::Dark, Color::Light, Color::Light, Color::Dark];
    let image: String = Renderer::<Dense1x2>::new(colors, 2, 1).build();

    assert_eq!(&image, " ▄  \n  ▀ ");

    let image2 = Renderer::<Dense1x2>::new(colors, 2, 1).module_dimensions(2, 2).build();

    assert_eq!(&image2, "        \n  ██    \n    ██  \n        ");
}

#[test]
fn integration_render_utf8_1x2() {
    use crate::render::unicode::Dense1x2;
    use crate::{EcLevel, QrCode, Version};

    let code = QrCode::with_version(b"09876542", Version::Micro(2), EcLevel::L).unwrap();
    let image = code.render::<Dense1x2>().module_dimensions(1, 1).build();
    assert_eq!(
        image,
        String::new()
            + "                 \n"
            + "  █▀▀▀▀▀█ ▀ █ ▀  \n"
            + "  █ ███ █  ▀ █   \n"
            + "  █ ▀▀▀ █  ▀█ █  \n"
            + "  ▀▀▀▀▀▀▀ ▄▀▀ █  \n"
            + "  ▀█ ▀▀▀▀▀██▀▀▄  \n"
            + "  ▀███▄ ▀▀ █ ██  \n"
            + "  ▀▀▀ ▀ ▀▀ ▀  ▀  \n"
            + "                 "
    )
}

#[test]
fn integration_render_utf8_1x2_inverted() {
    use crate::render::unicode::Dense1x2;
    use crate::{EcLevel, QrCode, Version};

    let code = QrCode::with_version(b"12345678", Version::Micro(2), EcLevel::L).unwrap();
    let image = code
        .render::<Dense1x2>()
        .dark_color(Dense1x2::Light)
        .light_color(Dense1x2::Dark)
        .module_dimensions(1, 1)
        .build();
    assert_eq!(
        image,
        "█████████████████\n\
         ██ ▄▄▄▄▄ █▄▀▄█▄██\n\
         ██ █   █ █   █ ██\n\
         ██ █▄▄▄█ █▄▄██▀██\n\
         ██▄▄▄▄▄▄▄█▄▄▄▀ ██\n\
         ██▄ ▀ ▀ ▀▄▄  ████\n\
         ██▄▄▀▄█ ▀▀▀ ▀▄▄██\n\
         ██▄▄▄█▄▄█▄██▄█▄██\n\
         ▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀"
    );
}