Implement `QRCode` widget

3 files changed, 318 insertions, 0 deletions

diff --git a/graphics/Cargo.toml b/graphics/Cargo.toml
index 1511f8b0..4ce50e5a 100644
--- a/graphics/Cargo.toml
+++ b/graphics/Cargo.toml
@@ -6,6 +6,7 @@ edition = "2018"
 
 [features]
 canvas = ["lyon"]
+qr_code = ["qrcode", "canvas"]
 font-source = ["font-kit"]
 font-fallback = []
 font-icons = []
@@ -32,6 +33,10 @@ path = "../style"
 version = "0.16"
 optional = true
 
+[dependencies.qrcode]
+version = "0.12"
+optional = true
+
 [dependencies.font-kit]
 version = "0.8"
 optional = true
diff --git a/graphics/src/widget.rs b/graphics/src/widget.rs
index f87b558a..159ca91b 100644
--- a/graphics/src/widget.rs
+++ b/graphics/src/widget.rs
@@ -63,3 +63,11 @@ pub mod canvas;
 #[cfg(feature = "canvas")]
 #[doc(no_inline)]
 pub use canvas::Canvas;
+
+#[cfg(feature = "qr_code")]
+#[cfg_attr(docsrs, doc(cfg(feature = "qr_code")))]
+pub mod qr_code;
+
+#[cfg(feature = "qr_code")]
+#[doc(no_inline)]
+pub use qr_code::QRCode;
diff --git a/graphics/src/widget/qr_code.rs b/graphics/src/widget/qr_code.rs
new file mode 100644
index 00000000..b3a01dd7
--- /dev/null
+++ b/graphics/src/widget/qr_code.rs
@@ -0,0 +1,305 @@
+//! Encode and display information in a QR code.
+use crate::canvas;
+use crate::{Backend, Defaults, Primitive, Renderer, Vector};
+
+use iced_native::{
+    layout, mouse, Color, Element, Hasher, Layout, Length, Point, Rectangle,
+    Size, Widget,
+};
+use thiserror::Error;
+
+const DEFAULT_CELL_SIZE: u16 = 4;
+const QUIET_ZONE: usize = 2;
+
+/// A type of matrix barcode consisting of squares arranged in a grid which
+/// can be read by an imaging device, such as a camera.
+#[derive(Debug)]
+pub struct QRCode<'a> {
+    state: &'a State,
+    dark: Color,
+    light: Color,
+    cell_size: u16,
+}
+
+impl<'a> QRCode<'a> {
+    /// Creates a new [`QRCode`] with the provided [`State`].
+    pub fn new(state: &'a State) -> Self {
+        Self {
+            cell_size: DEFAULT_CELL_SIZE,
+            dark: Color::BLACK,
+            light: Color::WHITE,
+            state,
+        }
+    }
+
+    /// Sets both the dark and light [`Color`]s of the [`QRCode`].
+    pub fn color(mut self, dark: Color, light: Color) -> Self {
+        self.dark = dark;
+        self.light = light;
+        self
+    }
+
+    /// Sets the size of the squares of the grid cell of the [`QRCode`].
+    pub fn cell_size(mut self, cell_size: u16) -> Self {
+        self.cell_size = cell_size;
+        self
+    }
+}
+
+impl<'a, Message, B> Widget<Message, Renderer<B>> for QRCode<'a>
+where
+    B: Backend,
+{
+    fn width(&self) -> Length {
+        Length::Shrink
+    }
+
+    fn height(&self) -> Length {
+        Length::Shrink
+    }
+
+    fn layout(
+        &self,
+        _renderer: &Renderer<B>,
+        _limits: &layout::Limits,
+    ) -> layout::Node {
+        let side_length = (self.state.width + 2 * QUIET_ZONE) as f32
+            * f32::from(self.cell_size);
+
+        layout::Node::new(Size::new(
+            f32::from(side_length),
+            f32::from(side_length),
+        ))
+    }
+
+    fn hash_layout(&self, state: &mut Hasher) {
+        use std::hash::Hash;
+
+        self.state.contents.hash(state);
+    }
+
+    fn draw(
+        &self,
+        _renderer: &mut Renderer<B>,
+        _defaults: &Defaults,
+        layout: Layout<'_>,
+        _cursor_position: Point,
+        _viewport: &Rectangle,
+    ) -> (Primitive, mouse::Interaction) {
+        let bounds = layout.bounds();
+        let side_length = self.state.width + 2 * QUIET_ZONE;
+
+        // Reuse cache if possible
+        let geometry = self.state.cache.draw(bounds.size(), |frame| {
+            // Scale units to cell size
+            frame.scale(f32::from(self.cell_size));
+
+            // Draw background
+            frame.fill_rectangle(
+                Point::ORIGIN,
+                Size::new(side_length as f32, side_length as f32),
+                self.light,
+            );
+
+            // Avoid drawing on the quiet zone
+            frame.translate(Vector::new(QUIET_ZONE as f32, QUIET_ZONE as f32));
+
+            // Draw contents
+            self.state
+                .contents
+                .iter()
+                .enumerate()
+                .filter(|(_, value)| **value == qrcode::Color::Dark)
+                .for_each(|(index, _)| {
+                    let row = index / self.state.width;
+                    let column = index % self.state.width;
+
+                    frame.fill_rectangle(
+                        Point::new(column as f32, row as f32),
+                        Size::UNIT,
+                        self.dark,
+                    );
+                });
+        });
+
+        (
+            Primitive::Translate {
+                translation: Vector::new(bounds.x, bounds.y),
+                content: Box::new(geometry.into_primitive()),
+            },
+            mouse::Interaction::default(),
+        )
+    }
+}
+
+impl<'a, Message, B> Into<Element<'a, Message, Renderer<B>>> for QRCode<'a>
+where
+    B: Backend,
+{
+    fn into(self) -> Element<'a, Message, Renderer<B>> {
+        Element::new(self)
+    }
+}
+
+/// The state of a [`QRCode`].
+///
+/// It stores the data that will be displayed.
+#[derive(Debug)]
+pub struct State {
+    contents: Vec<qrcode::Color>,
+    width: usize,
+    cache: canvas::Cache,
+}
+
+impl State {
+    /// Creates a new [`State`] with the provided data.
+    ///
+    /// This method uses an [`ErrorCorrection::Medium`] and chooses the smallest
+    /// size to display the data.
+    pub fn new(data: impl AsRef<[u8]>) -> Result<Self, Error> {
+        let encoded = qrcode::QrCode::new(data)?;
+
+        Ok(Self::build(encoded))
+    }
+
+    /// Creates a new [`State`] with the provided [`ErrorCorrection`].
+    pub fn with_error_correction(
+        data: impl AsRef<[u8]>,
+        error_correction: ErrorCorrection,
+    ) -> Result<Self, Error> {
+        let encoded = qrcode::QrCode::with_error_correction_level(
+            data,
+            error_correction.into(),
+        )?;
+
+        Ok(Self::build(encoded))
+    }
+
+    /// Creates a new [`State`] with the provided [`Version`] and
+    /// [`ErrorCorrection`].
+    pub fn with_version(
+        data: impl AsRef<[u8]>,
+        version: Version,
+        error_correction: ErrorCorrection,
+    ) -> Result<Self, Error> {
+        let encoded = qrcode::QrCode::with_version(
+            data,
+            version.into(),
+            error_correction.into(),
+        )?;
+
+        Ok(Self::build(encoded))
+    }
+
+    fn build(encoded: qrcode::QrCode) -> Self {
+        let width = encoded.width();
+        let contents = encoded.into_colors();
+
+        Self {
+            contents,
+            width,
+            cache: canvas::Cache::new(),
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+/// The size of a [`QRCode`].
+///
+/// The higher the version the larger the grid of cells, and therefore the more
+/// information the [`QRCode`] can carry.
+pub enum Version {
+    /// A normal QR code version. It should be between 1 and 40.
+    Normal(u8),
+
+    /// A micro QR code version. It should be between 1 and 4.
+    Micro(u8),
+}
+
+impl From<Version> for qrcode::Version {
+    fn from(version: Version) -> Self {
+        match version {
+            Version::Normal(v) => qrcode::Version::Normal(i16::from(v)),
+            Version::Micro(v) => qrcode::Version::Micro(i16::from(v)),
+        }
+    }
+}
+
+/// The error correction level.
+///
+/// It controls the amount of data that can be damaged while still being able
+/// to recover the original information.
+///
+/// A higher error correction level allows for more corrupted data.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ErrorCorrection {
+    /// Low error correction. 7% of the data can be restored.
+    Low,
+    /// Medium error correction. 15% of the data can be restored.
+    Medium,
+    /// Quartile error correction. 25% of the data can be restored.
+    Quartile,
+    /// High error correction. 30% of the data can be restored.
+    High,
+}
+
+impl From<ErrorCorrection> for qrcode::EcLevel {
+    fn from(ec_level: ErrorCorrection) -> Self {
+        match ec_level {
+            ErrorCorrection::Low => qrcode::EcLevel::L,
+            ErrorCorrection::Medium => qrcode::EcLevel::M,
+            ErrorCorrection::Quartile => qrcode::EcLevel::Q,
+            ErrorCorrection::High => qrcode::EcLevel::H,
+        }
+    }
+}
+
+/// An error that occurred when building a [`State`] for a [`QRCode`].
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Error)]
+pub enum Error {
+    /// The data is too long to encode in a QR code for the chosen [`Version`].
+    #[error(
+        "The data is too long to encode in a QR code for the chosen version"
+    )]
+    DataTooLong,
+
+    /// The chosen [`Version`] and [`ErrorCorrection`] combination is invalid.
+    #[error(
+        "The chosen version and error correction level combination is invalid."
+    )]
+    InvalidVersion,
+
+    /// One or more characters in the provided data are not supported by the
+    /// chosen [`Version`].
+    #[error(
+        "One or more characters in the provided data are not supported by the \
+        chosen version"
+    )]
+    UnsupportedCharacterSet,
+
+    /// The chosen ECI designator is invalid. A valid designator should be
+    /// between 0 and 999999.
+    #[error(
+        "The chosen ECI designator is invalid. A valid designator should be \
+        between 0 and 999999."
+    )]
+    InvalidEciDesignator,
+
+    /// A character that does not belong to the character set was found.
+    #[error("A character that does not belong to the character set was found")]
+    InvalidCharacter,
+}
+
+impl From<qrcode::types::QrError> for Error {
+    fn from(error: qrcode::types::QrError) -> Self {
+        use qrcode::types::QrError;
+
+        match error {
+            QrError::DataTooLong => Error::DataTooLong,
+            QrError::InvalidVersion => Error::InvalidVersion,
+            QrError::UnsupportedCharacterSet => Error::UnsupportedCharacterSet,
+            QrError::InvalidEciDesignator => Error::InvalidEciDesignator,
+            QrError::InvalidCharacter => Error::InvalidCharacter,
+        }
+    }
+}