//! Utility functions for drawing QR codes generated using `qrcodegen`
//! to a canvas provided by the `image` crate.
use image::Luma;
pub use image;
pub use qrcodegen;
/// Draw a QR code to an image buffer.
pub fn draw_canvas(qr: qrcodegen::QrCode) -> image::ImageBuffer<Luma<u8>, Vec<u8>> {
let size = qr.size() as u32;
// "+ 8 * 8" is here to add padding (the white border around the QRCode)
// As some QRCode readers don't work without padding
let image_size = size * 8 + 8 * 8;
let mut canvas = image::GrayImage::new(image_size, image_size);
// Draw the border
for x in 0..image_size {
for y in 0..image_size {
if (y < 8 * 4 || y >= image_size - 8 * 4) || (x < 8 * 4 || x >= image_size - 8 * 4) {
canvas.put_pixel(x, y, Luma([255]));
}
}
}
// The QR inside the white border
for x_qr in 0..size {
for y_qr in 0..size {
// The canvas is a grayscale image without alpha. Hence it's only one 8-bits byte longs
// This clever trick to one-line the value was achieved with advanced mathematics
// And deep understanding of Boolean algebra.
let val = !qr.get_module(x_qr as i32, y_qr as i32) as u8 * 255;
// Multiply coordinates by width of pixels
// And take into account the 8*4 padding on top and left side
let x_start = x_qr * 8 + 8 * 4;
let y_start = y_qr * 8 + 8 * 4;
// Draw a 8-pixels-wide square
for x_img in x_start..x_start + 8 {
for y_img in y_start..y_start + 8 {
canvas.put_pixel(x_img, y_img, Luma([val]));
}
}
}
}
canvas
}
/// Draw text to a PNG QR code.
pub fn draw_png(text: &str) -> Result<Vec<u8>, String> {
use image::ImageEncoder;
let mut vec = Vec::new();
let qr: Result<qrcodegen::QrCode, String> =
match qrcodegen::QrCode::encode_text(text, qrcodegen::QrCodeEcc::Medium) {
Ok(qr) => Ok(qr),
Err(err) => Err(err.to_string()),
};
if qr.is_err() {
return Err(qr.err().unwrap());
}
let code = qr?;
// "+ 8 * 8" is here to add padding (the white border around the QRCode)
// As some QRCode readers don't work without padding
let image_size = (code.size() as u32) * 8 + 8 * 8;
let canvas = draw_canvas(code);
// Encode the canvas into a PNG
let encoder = image::codecs::png::PngEncoder::new(&mut vec);
match encoder.write_image(
&canvas.into_raw(),
image_size,
image_size,
image::ColorType::L8,
) {
Ok(_) => Ok(vec),
Err(err) => Err(err.to_string()),
}
}
/// Draw text to a Base64-encoded PNG QR code.
#[cfg(feature = "base64")]
pub fn draw_base64(text: &str) -> Result<String, String> {
use base64::{engine::general_purpose, Engine as _};
Ok(draw_png(text).map(|vec| general_purpose::STANDARD.encode(vec))?)
}
