QR Code Generator

A QR (Quick Response) code is a type of two-dimensional barcode, first designed in 1994 for the automotive industry in Japan. It is an optical label that is machine-readable and stores information in a matrix of black squares on a white background. Unlike traditional one-dimensional barcodes, which can only store a small amount of information in a single line, QR codes can store significantly more data, including URLs, text, contact information (vCards), Wi-Fi network details, and more.

Key features of QR codes include:
- High Data Capacity: They can store hundreds of times more information than conventional barcodes.
- Error Correction: QR codes incorporate error correction (Reed-Solomon error correction), allowing them to be scanned even if part of the code is damaged, dirty, or obscured. There are four error correction levels (L, M, Q, H), with 'L' being the lowest (7% of data can be restored) and 'H' being the highest (30% of data can be restored).
- Omnidirectional Readability: They can be read from any direction (360 degrees) due to their distinctive finder patterns at three corners.

How a QR Code Generator Works (Simplified Process):
1. Input Data: The generator takes the desired text, URL, or other data as input.
2. Data Encoding: The input data is converted into a sequence of bits according to a specific encoding mode (numeric, alphanumeric, byte, or Kanji).
3. Error Correction Encoding: Redundant data is added using Reed-Solomon error correction codes. The amount of redundancy depends on the chosen error correction level.
4. Structure and Arrangement: The data bits and error correction bits are arranged into a series of 'modules' (the black and white squares). Fixed patterns like finder patterns (for position), alignment patterns (for perspective correction), timing patterns (for module coordinates), and format information (for error correction level and mask pattern) are added.
5. Masking: A mask pattern is applied to ensure a good balance of dark and light modules, preventing large, unvarying areas that could be difficult for scanners to read.
6. Quiet Zone: A mandatory white border (quiet zone) is added around the entire code to separate it from surrounding content, aiding scanning.
7. Rendering: Finally, the structured module matrix is rendered into a visual image (e.g., PNG, SVG, or console ASCII art) that can be displayed or printed.

QR code generators are widely used in marketing, logistics, ticketing, payments, and many other applications to provide quick access to information via smartphone cameras.

Example Code

```rust
// To run this code, add the following to your Cargo.toml:
// [dependencies]
// qrcode-rs = "0.13"

use qrcode_rs::QrCode;
use qrcode_rs::EcLevel;

fn main() {
    // The text or data you want to encode into the QR code
    let data_to_encode = "https://www.rust-lang.org/";

    println!("Generating QR Code for: '{}'\n", data_to_encode);

    // Create a new QR code instance.
    // We specify EcLevel::M for Medium error correction, which means
    // about 15% of the code can be damaged and still be readable.
    let code = QrCode::new(data_to_encode.as_bytes())
        .expect("Failed to create QR code. Data might be too long or invalid.");

    // Render the QR code to a string using ASCII block characters for display in the console.
    // - `quiet_zone(true)` adds a necessary white border around the QR code.
    // - `light_color("  ")` defines two spaces for a 'light' module.
    // - `dark_color("██")` defines two block characters for a 'dark' module.
    let qr_string = code.render()
        .quiet_zone(true)
        .light_color("  ")
        .dark_color("██")
        .build();

    // Print the generated QR code to the console
    println!("{}", qr_string);

    // You can also save the QR code as an image (e.g., PNG) by enabling the 'image' feature
    // in your Cargo.toml for qrcode-rs:
    // qrcode-rs = { version = "0.13", features = ["image"] }
    // And adding 'image = "0.24"' as a direct dependency.
    /*
    #[cfg(feature = "image")]
    {
        use qrcode_rs::image::QrCodeImage;
        println!("\nSaving QR code to 'qrcode.png'...");
        let image = code.render::<QrCodeImage>()
            .dark_color([0, 0, 0, 255]) // Black
            .light_color([255, 255, 255, 255]) // White
            .build();
        image.save("qrcode.png").expect("Failed to save QR code image");
        println!("QR code saved as 'qrcode.png'");
    }
    */
}
```

Example Code

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