palette/alpha/

alpha.rs

use core::{
    fmt,
    iter::FromIterator,
    ops::{
        Add, AddAssign, BitAnd, Deref, DerefMut, Div, DivAssign, Mul, MulAssign, Sub, SubAssign,
    },
};

#[cfg(feature = "approx")]
use approx::{AbsDiffEq, RelativeEq, UlpsEq};
#[cfg(feature = "random")]
use rand::{
    distributions::{
        uniform::{SampleBorrow, SampleUniform, Uniform, UniformSampler},
        Distribution, Standard,
    },
    Rng,
};

use crate::{
    blend::{PreAlpha, Premultiply},
    bool_mask::HasBoolMask,
    cast::ArrayCast,
    clamp, clamp_assign,
    convert::{FromColorUnclamped, IntoColorUnclamped},
    num::{self, Arithmetics, One, PartialCmp, SaturatingAdd, SaturatingSub, Zero},
    stimulus::Stimulus,
    ArrayExt, Clamp, ClampAssign, GetHue, IsWithinBounds, Lighten, LightenAssign, Mix, MixAssign,
    NextArray, Saturate, SaturateAssign, SetHue, ShiftHue, ShiftHueAssign, WithAlpha, WithHue,
};

/// An alpha component wrapper for colors, for adding transparency.
///
/// Instead of having separate types for "RGB with alpha", "HSV with alpha", and
/// so on, Palette uses this wrapper type to attach the alpha component. The
/// memory representation is the same as if `alpha` was the last member/property
/// of `color`, which is just as space efficient. The perk of having a wrapper
/// is that the alpha can easily be added to or separated form any color.
///
/// # Creating Transparent Values
///
/// The color types in Palette have transparent type aliases, such as
/// [`Srgba`](crate::Srgba) for [`Srgb`][crate::Srgb] or [`Hsla`](crate::Hsla)
/// for [`Hsl`](crate::Hsl). These aliases implement `new` and other useful
/// methods. Here's the same example as for [`Rgb`](crate::rgb::Rgb), but with
/// transparency:
///
/// ```
/// use palette::Srgba;
///
/// let rgba_u8 = Srgba::new(171u8, 193, 35, 128);
/// let rgab_f32 = Srgba::new(0.3f32, 0.8, 0.1, 0.5);
///
/// // `new` is also `const`:
/// const RGBA_U8: Srgba<u8> = Srgba::new(171, 193, 35, 128);
///
/// // Conversion methods from the color type are usually available for transparent
/// // values too. For example `into_format` for changing the number format:
/// let rgb_u8_from_f32 = Srgba::new(0.3f32, 0.8, 0.1, 0.5).into_format::<u8, u8>();
///
/// // Hexadecimal is also supported for RGBA, with or without the #:
/// let rgb_from_hex1: Srgba<u8> = "#f034e65a".parse().unwrap();
/// let rgb_from_hex2: Srgba<u8> = "f034e65a".parse().unwrap();
/// assert_eq!(rgb_from_hex1, rgb_from_hex2);
///
/// // This includes the shorthand format:
/// let rgb_from_short_hex: Srgba<u8> = "f3ea".parse().unwrap();
/// let rgb_from_long_hex: Srgba<u8> = "ff33eeaa".parse().unwrap();
/// assert_eq!(rgb_from_short_hex, rgb_from_long_hex);
///
/// // It's also possible to convert from (and to) arrays, tuples and `u32` values:
/// let rgb_from_array = Srgba::from([171u8, 193, 35, 128]);
/// let rgb_from_tuple = Srgba::from((171u8, 193, 35, 128));
/// let rgb_from_u32 = Srgba::from(0x607F005A);
/// ```
///
/// Opaque values can be made transparent using the [`WithAlpha`] trait, in
/// addition to simply wrapping them in `Alpha`. [`WithAlpha`] is also useful in
/// generic code, since it's implemented for both opaque and transparent types.
///
/// ```
/// use palette::{WithAlpha, Srgb};
///
/// let rgb = Srgb::new(171u8, 193, 35);
/// let rgba = rgb.with_alpha(128u8);
/// assert_eq!(rgba.alpha, 128);
/// ```
///
/// You may have noticed the `u8` in `rgb.with_alpha(128u8)`. That's because
/// `Alpha` allows the transparency component to have a different type than the
/// color components. It would be just as valid to write
/// `rgb.with_alpha(0.5f32)`, for example.
///
/// # Accessing Color Components
///
/// To help with the nesting, `Alpha` implements [`Deref`] and [`DerefMut`].
/// This use of the traits is a bit unconventional, since `Alpha` isn't a smart
/// pointer. It turned out to be a quite successful experiment that stuck
/// around.
///
/// ```
/// use palette::Srgba;
///
/// let rgba = Srgba::new(171u8, 193, 35, 128);
/// let red = rgba.red; // Accesses `rgba.color.red`.
/// let alpha = rgba.alpha; // Accesses `rgba.alpha`.
/// let rgb = rgba.color; // Accesses `rgba.color`;
/// ```
///
/// The main drawback is in generic code:
///
/// ```compile_fail
/// use palette::Srgba;
///
/// fn get_red<T>(rgba: Srgba<T>) -> T {
///     rgba.red // Error: cannot move out of dereference of `Alpha<Rgb<_, T>, T>`
/// }
/// ```
///
/// `red` has to be accessed through `color`:
///
/// ```
/// use palette::Srgba;
///
/// fn get_red<T>(rgba: Srgba<T>) -> T {
///     rgba.color.red
/// }
/// ```
#[derive(Clone, Copy, Debug)]
#[repr(C)]
pub struct Alpha<C, T> {
    /// The color.
    pub color: C,

    /// The transparency component. 0.0 (or 0u8) is fully transparent and 1.0
    /// (or 255u8) is fully opaque.
    pub alpha: T,
}

impl<C, A> Alpha<C, A> {
    /// Return an iterator over the colors in the wrapped collections.
    pub fn iter<'a>(&'a self) -> <&'a Self as IntoIterator>::IntoIter
    where
        &'a Self: IntoIterator,
    {
        self.into_iter()
    }

    /// Return an iterator that allows modifying the colors in the wrapped collections.
    pub fn iter_mut<'a>(&'a mut self) -> <&'a mut Self as IntoIterator>::IntoIter
    where
        &'a mut Self: IntoIterator,
    {
        self.into_iter()
    }
}

impl<C: Premultiply> Alpha<C, C::Scalar> {
    /// Alpha mask the color by its transparency.
    pub fn premultiply(self) -> PreAlpha<C> {
        PreAlpha::new(self.color, self.alpha)
    }
}

impl<C, T: Stimulus> Alpha<C, T> {
    /// Return the `alpha` value minimum.
    pub fn min_alpha() -> T {
        T::zero()
    }

    /// Return the `alpha` value maximum.
    pub fn max_alpha() -> T {
        T::max_intensity()
    }
}

impl<C, T> PartialEq for Alpha<C, T>
where
    T: PartialEq,
    C: PartialEq,
{
    fn eq(&self, other: &Self) -> bool {
        self.color == other.color && self.alpha == other.alpha
    }
}

impl<C, T> Eq for Alpha<C, T>
where
    T: Eq,
    C: Eq,
{
}

impl<C1: WithAlpha<T>, C2, T> FromColorUnclamped<C1> for Alpha<C2, T>
where
    C1::Color: IntoColorUnclamped<C2>,
{
    fn from_color_unclamped(other: C1) -> Self {
        let (color, alpha) = other.split();

        Alpha {
            color: color.into_color_unclamped(),
            alpha,
        }
    }
}

impl<C, A> WithAlpha<A> for Alpha<C, A> {
    type Color = C;
    type WithAlpha = Self;

    fn with_alpha(mut self, alpha: A) -> Self::WithAlpha {
        self.alpha = alpha;
        self
    }

    fn without_alpha(self) -> Self::Color {
        self.color
    }

    fn split(self) -> (Self::Color, A) {
        (self.color, self.alpha)
    }
}

impl<C, T> Deref for Alpha<C, T> {
    type Target = C;

    fn deref(&self) -> &C {
        &self.color
    }
}

impl<C, T> DerefMut for Alpha<C, T> {
    fn deref_mut(&mut self) -> &mut C {
        &mut self.color
    }
}

impl<C> Mix for Alpha<C, C::Scalar>
where
    C: Mix,
    C::Scalar: Zero + One + num::Clamp + Arithmetics + Clone,
{
    type Scalar = C::Scalar;

    #[inline]
    fn mix(mut self, other: Self, factor: C::Scalar) -> Self {
        let factor = clamp(factor, C::Scalar::zero(), C::Scalar::one());

        self.color = self.color.mix(other.color, factor.clone());
        self.alpha = self.alpha.clone() + factor * (other.alpha - self.alpha);

        self
    }
}

impl<C> MixAssign for Alpha<C, C::Scalar>
where
    C: MixAssign,
    C::Scalar: Zero + One + num::Clamp + Arithmetics + AddAssign + Clone,
{
    type Scalar = C::Scalar;

    #[inline]
    fn mix_assign(&mut self, other: Self, factor: C::Scalar) {
        let factor = clamp(factor, C::Scalar::zero(), C::Scalar::one());

        self.color.mix_assign(other.color, factor.clone());
        self.alpha += factor * (other.alpha - self.alpha.clone());
    }
}

impl<C: Lighten> Lighten for Alpha<C, C::Scalar> {
    type Scalar = C::Scalar;

    #[inline]
    fn lighten(self, factor: C::Scalar) -> Self {
        Alpha {
            color: self.color.lighten(factor),
            alpha: self.alpha,
        }
    }

    #[inline]
    fn lighten_fixed(self, amount: C::Scalar) -> Self {
        Alpha {
            color: self.color.lighten_fixed(amount),
            alpha: self.alpha,
        }
    }
}

impl<C: LightenAssign> LightenAssign for Alpha<C, C::Scalar> {
    type Scalar = C::Scalar;

    #[inline]
    fn lighten_assign(&mut self, factor: C::Scalar) {
        self.color.lighten_assign(factor);
    }

    #[inline]
    fn lighten_fixed_assign(&mut self, amount: C::Scalar) {
        self.color.lighten_fixed_assign(amount);
    }
}

impl<C: GetHue, T> GetHue for Alpha<C, T> {
    type Hue = C::Hue;

    #[inline]
    fn get_hue(&self) -> C::Hue {
        self.color.get_hue()
    }
}

impl<C, T, H> WithHue<H> for Alpha<C, T>
where
    C: WithHue<H>,
{
    #[inline]
    fn with_hue(mut self, hue: H) -> Self {
        self.color = self.color.with_hue(hue);
        self
    }
}

impl<C, T, H> SetHue<H> for Alpha<C, T>
where
    C: SetHue<H>,
{
    #[inline]
    fn set_hue(&mut self, hue: H) {
        self.color.set_hue(hue);
    }
}

impl<C, T> ShiftHue for Alpha<C, T>
where
    C: ShiftHue,
{
    type Scalar = C::Scalar;

    #[inline]
    fn shift_hue(mut self, amount: Self::Scalar) -> Self {
        self.color = self.color.shift_hue(amount);
        self
    }
}

impl<C, T> ShiftHueAssign for Alpha<C, T>
where
    C: ShiftHueAssign,
{
    type Scalar = C::Scalar;

    #[inline]
    fn shift_hue_assign(&mut self, amount: Self::Scalar) {
        self.color.shift_hue_assign(amount);
    }
}

impl<C: Saturate> Saturate for Alpha<C, C::Scalar> {
    type Scalar = C::Scalar;

    #[inline]
    fn saturate(self, factor: C::Scalar) -> Self {
        Alpha {
            color: self.color.saturate(factor),
            alpha: self.alpha,
        }
    }

    #[inline]
    fn saturate_fixed(self, amount: C::Scalar) -> Self {
        Alpha {
            color: self.color.saturate_fixed(amount),
            alpha: self.alpha,
        }
    }
}

impl<C: SaturateAssign> SaturateAssign for Alpha<C, C::Scalar> {
    type Scalar = C::Scalar;

    #[inline]
    fn saturate_assign(&mut self, factor: C::Scalar) {
        self.color.saturate_assign(factor);
    }

    #[inline]
    fn saturate_fixed_assign(&mut self, amount: C::Scalar) {
        self.color.saturate_fixed_assign(amount);
    }
}

impl<C, T> IsWithinBounds for Alpha<C, T>
where
    C: IsWithinBounds,
    T: Stimulus + PartialCmp + IsWithinBounds<Mask = C::Mask>,
    C::Mask: BitAnd<Output = C::Mask>,
{
    #[inline]
    fn is_within_bounds(&self) -> C::Mask {
        self.color.is_within_bounds()
            & self.alpha.gt_eq(&Self::min_alpha())
            & self.alpha.lt_eq(&Self::max_alpha())
    }
}

impl<C, T> Clamp for Alpha<C, T>
where
    C: Clamp,
    T: Stimulus + num::Clamp,
{
    #[inline]
    fn clamp(self) -> Self {
        Alpha {
            color: self.color.clamp(),
            alpha: clamp(self.alpha, Self::min_alpha(), Self::max_alpha()),
        }
    }
}

impl<C, T> ClampAssign for Alpha<C, T>
where
    C: ClampAssign,
    T: Stimulus + num::ClampAssign,
{
    #[inline]
    fn clamp_assign(&mut self) {
        self.color.clamp_assign();
        clamp_assign(&mut self.alpha, Self::min_alpha(), Self::max_alpha());
    }
}

unsafe impl<C> ArrayCast for Alpha<C, <<C as ArrayCast>::Array as ArrayExt>::Item>
where
    C: ArrayCast,
    C::Array: NextArray,
{
    type Array = <C::Array as NextArray>::Next;
}

impl<C, T> HasBoolMask for Alpha<C, T>
where
    C: HasBoolMask,
    T: HasBoolMask<Mask = C::Mask>,
{
    type Mask = C::Mask;
}

impl<C: Default, T: Stimulus> Default for Alpha<C, T> {
    fn default() -> Alpha<C, T> {
        Alpha {
            color: C::default(),
            alpha: Self::max_alpha(),
        }
    }
}

#[cfg(feature = "approx")]
impl<C, T> AbsDiffEq for Alpha<C, T>
where
    C: AbsDiffEq<Epsilon = T::Epsilon>,
    T: AbsDiffEq,
    T::Epsilon: Clone,
{
    type Epsilon = T::Epsilon;

    fn default_epsilon() -> Self::Epsilon {
        T::default_epsilon()
    }

    fn abs_diff_eq(&self, other: &Self, epsilon: T::Epsilon) -> bool {
        self.color.abs_diff_eq(&other.color, epsilon.clone())
            && self.alpha.abs_diff_eq(&other.alpha, epsilon)
    }
}

#[cfg(feature = "approx")]
impl<C, T> RelativeEq for Alpha<C, T>
where
    C: RelativeEq<Epsilon = T::Epsilon>,
    T: RelativeEq,
    T::Epsilon: Clone,
{
    fn default_max_relative() -> Self::Epsilon {
        T::default_max_relative()
    }

    fn relative_eq(
        &self,
        other: &Alpha<C, T>,
        epsilon: Self::Epsilon,
        max_relative: Self::Epsilon,
    ) -> bool {
        self.color
            .relative_eq(&other.color, epsilon.clone(), max_relative.clone())
            && self.alpha.relative_eq(&other.alpha, epsilon, max_relative)
    }
}

#[cfg(feature = "approx")]
impl<C, T> UlpsEq for Alpha<C, T>
where
    C: UlpsEq<Epsilon = T::Epsilon>,
    T: UlpsEq,
    T::Epsilon: Clone,
{
    fn default_max_ulps() -> u32 {
        T::default_max_ulps()
    }

    fn ulps_eq(&self, other: &Alpha<C, T>, epsilon: Self::Epsilon, max_ulps: u32) -> bool {
        self.color.ulps_eq(&other.color, epsilon.clone(), max_ulps)
            && self.alpha.ulps_eq(&other.alpha, epsilon, max_ulps)
    }
}

impl<C, T> Add for Alpha<C, T>
where
    C: Add,
    T: Add,
{
    type Output = Alpha<C::Output, <T as Add>::Output>;

    fn add(self, other: Alpha<C, T>) -> Self::Output {
        Alpha {
            color: self.color + other.color,
            alpha: self.alpha + other.alpha,
        }
    }
}

impl<T, C> Add<T> for Alpha<C, T>
where
    T: Add + Clone,
    C: Add<T>,
{
    type Output = Alpha<C::Output, <T as Add>::Output>;

    fn add(self, c: T) -> Self::Output {
        Alpha {
            color: self.color + c.clone(),
            alpha: self.alpha + c,
        }
    }
}

impl<C, T> AddAssign for Alpha<C, T>
where
    C: AddAssign,
    T: AddAssign,
{
    fn add_assign(&mut self, other: Alpha<C, T>) {
        self.color += other.color;
        self.alpha += other.alpha;
    }
}

impl<T, C> AddAssign<T> for Alpha<C, T>
where
    T: AddAssign + Clone,
    C: AddAssign<T>,
{
    fn add_assign(&mut self, c: T) {
        self.color += c.clone();
        self.alpha += c;
    }
}

impl<C, T> SaturatingAdd for Alpha<C, T>
where
    C: SaturatingAdd,
    T: SaturatingAdd,
{
    type Output = Alpha<C::Output, <T as SaturatingAdd>::Output>;

    fn saturating_add(self, other: Alpha<C, T>) -> Self::Output {
        Alpha {
            color: self.color.saturating_add(other.color),
            alpha: self.alpha.saturating_add(other.alpha),
        }
    }
}

impl<T, C> SaturatingAdd<T> for Alpha<C, T>
where
    T: SaturatingAdd + Clone,
    C: SaturatingAdd<T>,
{
    type Output = Alpha<C::Output, <T as SaturatingAdd>::Output>;

    fn saturating_add(self, c: T) -> Self::Output {
        Alpha {
            color: self.color.saturating_add(c.clone()),
            alpha: self.alpha.saturating_add(c),
        }
    }
}

impl<C, T> Sub for Alpha<C, T>
where
    C: Sub,
    T: Sub,
{
    type Output = Alpha<C::Output, <T as Sub>::Output>;

    fn sub(self, other: Alpha<C, T>) -> Self::Output {
        Alpha {
            color: self.color - other.color,
            alpha: self.alpha - other.alpha,
        }
    }
}

impl<T, C> Sub<T> for Alpha<C, T>
where
    T: Sub + Clone,
    C: Sub<T>,
{
    type Output = Alpha<C::Output, <T as Sub>::Output>;

    fn sub(self, c: T) -> Self::Output {
        Alpha {
            color: self.color - c.clone(),
            alpha: self.alpha - c,
        }
    }
}

impl<C, T> SubAssign for Alpha<C, T>
where
    C: SubAssign,
    T: SubAssign,
{
    fn sub_assign(&mut self, other: Alpha<C, T>) {
        self.color -= other.color;
        self.alpha -= other.alpha;
    }
}

impl<T, C> SubAssign<T> for Alpha<C, T>
where
    T: SubAssign + Clone,
    C: SubAssign<T>,
{
    fn sub_assign(&mut self, c: T) {
        self.color -= c.clone();
        self.alpha -= c;
    }
}

impl<C, T> SaturatingSub for Alpha<C, T>
where
    C: SaturatingSub,
    T: SaturatingSub,
{
    type Output = Alpha<C::Output, <T as SaturatingSub>::Output>;

    fn saturating_sub(self, other: Alpha<C, T>) -> Self::Output {
        Alpha {
            color: self.color.saturating_sub(other.color),
            alpha: self.alpha.saturating_sub(other.alpha),
        }
    }
}

impl<T, C> SaturatingSub<T> for Alpha<C, T>
where
    T: SaturatingSub + Clone,
    C: SaturatingSub<T>,
{
    type Output = Alpha<C::Output, <T as SaturatingSub>::Output>;

    fn saturating_sub(self, c: T) -> Self::Output {
        Alpha {
            color: self.color.saturating_sub(c.clone()),
            alpha: self.alpha.saturating_sub(c),
        }
    }
}

impl<C, T> Mul for Alpha<C, T>
where
    C: Mul,
    T: Mul,
{
    type Output = Alpha<C::Output, <T as Mul>::Output>;

    fn mul(self, other: Alpha<C, T>) -> Self::Output {
        Alpha {
            color: self.color * other.color,
            alpha: self.alpha * other.alpha,
        }
    }
}

impl<T, C> Mul<T> for Alpha<C, T>
where
    T: Mul + Clone,
    C: Mul<T>,
{
    type Output = Alpha<C::Output, <T as Mul>::Output>;

    fn mul(self, c: T) -> Self::Output {
        Alpha {
            color: self.color * c.clone(),
            alpha: self.alpha * c,
        }
    }
}

impl<C, T> MulAssign for Alpha<C, T>
where
    C: MulAssign,
    T: MulAssign,
{
    fn mul_assign(&mut self, other: Alpha<C, T>) {
        self.color *= other.color;
        self.alpha *= other.alpha;
    }
}

impl<T, C> MulAssign<T> for Alpha<C, T>
where
    T: MulAssign + Clone,
    C: MulAssign<T>,
{
    fn mul_assign(&mut self, c: T) {
        self.color *= c.clone();
        self.alpha *= c;
    }
}

impl<C, T> Div for Alpha<C, T>
where
    C: Div,
    T: Div,
{
    type Output = Alpha<C::Output, <T as Div>::Output>;

    fn div(self, other: Alpha<C, T>) -> Self::Output {
        Alpha {
            color: self.color / other.color,
            alpha: self.alpha / other.alpha,
        }
    }
}

impl<T, C> Div<T> for Alpha<C, T>
where
    T: Div + Clone,
    C: Div<T>,
{
    type Output = Alpha<C::Output, <T as Div>::Output>;

    fn div(self, c: T) -> Self::Output {
        Alpha {
            color: self.color / c.clone(),
            alpha: self.alpha / c,
        }
    }
}

impl<C, T> DivAssign for Alpha<C, T>
where
    C: DivAssign,
    T: DivAssign,
{
    fn div_assign(&mut self, other: Alpha<C, T>) {
        self.color /= other.color;
        self.alpha /= other.alpha;
    }
}

impl<T, C> DivAssign<T> for Alpha<C, T>
where
    T: DivAssign + Clone,
    C: DivAssign<T>,
{
    fn div_assign(&mut self, c: T) {
        self.color /= c.clone();
        self.alpha /= c;
    }
}

impl_array_casts!([C, T, const N: usize] Alpha<C, T>, [T; N], where Alpha<C, T>: ArrayCast<Array = [T; N]>);

impl<C, T: Stimulus> From<C> for Alpha<C, T> {
    fn from(color: C) -> Alpha<C, T> {
        Alpha {
            color,
            alpha: Self::max_alpha(),
        }
    }
}

impl<C, T> fmt::LowerHex for Alpha<C, T>
where
    T: fmt::LowerHex,
    C: fmt::LowerHex,
{
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let size = f.width().unwrap_or(::core::mem::size_of::<T>() * 2);
        write!(
            f,
            "{:0width$x}{:0width$x}",
            self.color,
            self.alpha,
            width = size
        )
    }
}

impl<C, T> fmt::UpperHex for Alpha<C, T>
where
    T: fmt::UpperHex,
    C: fmt::UpperHex,
{
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let size = f.width().unwrap_or(::core::mem::size_of::<T>() * 2);
        write!(
            f,
            "{:0width$X}{:0width$X}",
            self.color,
            self.alpha,
            width = size
        )
    }
}

impl<Tc, Ta, C, A> Extend<Alpha<Tc, Ta>> for Alpha<C, A>
where
    C: Extend<Tc>,
    A: Extend<Ta>,
{
    fn extend<T: IntoIterator<Item = Alpha<Tc, Ta>>>(&mut self, iter: T) {
        for color in iter {
            self.color.extend(core::iter::once(color.color));
            self.alpha.extend(core::iter::once(color.alpha));
        }
    }
}

impl<Tc, Ta, C, A> FromIterator<Alpha<Tc, Ta>> for Alpha<C, A>
where
    C: Extend<Tc> + FromIterator<Tc>,
    A: Extend<Ta> + Default,
{
    fn from_iter<T: IntoIterator<Item = Alpha<Tc, Ta>>>(iter: T) -> Self {
        let mut result = Self {
            color: C::from_iter(None), // Default is currently a used for black, meaning it's not always what we want here.
            alpha: A::default(),
        };

        for color in iter {
            result.color.extend(core::iter::once(color.color));
            result.alpha.extend(core::iter::once(color.alpha));
        }

        result
    }
}

/// An iterator for transparent colors.
pub struct Iter<C, A> {
    pub(crate) color: C,
    pub(crate) alpha: A,
}

impl<C, A> Iterator for Iter<C, A>
where
    C: Iterator,
    A: Iterator,
{
    type Item = Alpha<C::Item, A::Item>;

    fn next(&mut self) -> Option<Self::Item> {
        let color = self.color.next();
        let alpha = self.alpha.next();

        if let (Some(color), Some(alpha)) = (color, alpha) {
            Some(Alpha { color, alpha })
        } else {
            None
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        let hint = self.color.size_hint();
        debug_assert_eq!(
            self.alpha.size_hint(),
            hint,
            "the color and alpha iterators have different size hints"
        );

        hint
    }

    fn count(self) -> usize {
        let count = self.color.count();
        debug_assert_eq!(
            self.alpha.count(),
            count,
            "the color and alpha iterators have different counts"
        );

        count
    }
}

impl<C, A> DoubleEndedIterator for Iter<C, A>
where
    C: DoubleEndedIterator,
    A: DoubleEndedIterator,
{
    fn next_back(&mut self) -> Option<Self::Item> {
        let color = self.color.next_back();
        let alpha = self.alpha.next_back();

        if let (Some(color), Some(alpha)) = (color, alpha) {
            Some(Alpha { color, alpha })
        } else {
            None
        }
    }
}

impl<C, A> ExactSizeIterator for Iter<C, A>
where
    C: ExactSizeIterator,
    A: ExactSizeIterator,
{
    fn len(&self) -> usize {
        let len = self.color.len();
        debug_assert_eq!(
            self.alpha.len(),
            len,
            "the color and alpha iterators have different lengths"
        );

        len
    }
}

#[cfg(feature = "serializing")]
impl<C, T> serde::Serialize for Alpha<C, T>
where
    C: serde::Serialize,
    T: serde::Serialize,
{
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: serde::Serializer,
    {
        self.color.serialize(crate::serde::AlphaSerializer {
            inner: serializer,
            alpha: &self.alpha,
        })
    }
}

#[cfg(feature = "serializing")]
impl<'de, C, T> serde::Deserialize<'de> for Alpha<C, T>
where
    C: serde::Deserialize<'de>,
    T: serde::Deserialize<'de>,
{
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        let mut alpha: Option<T> = None;

        let color = C::deserialize(crate::serde::AlphaDeserializer {
            inner: deserializer,
            alpha: &mut alpha,
        })?;

        if let Some(alpha) = alpha {
            Ok(Self { color, alpha })
        } else {
            Err(serde::de::Error::missing_field("alpha"))
        }
    }
}

#[cfg(feature = "random")]
impl<C, T> Distribution<Alpha<C, T>> for Standard
where
    Standard: Distribution<C> + Distribution<T>,
{
    fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> Alpha<C, T> {
        Alpha {
            color: rng.gen(),
            alpha: rng.gen(),
        }
    }
}

/// Sample transparent colors uniformly.
#[cfg(feature = "random")]
pub struct UniformAlpha<C, T>
where
    T: SampleUniform,
    C: SampleUniform,
{
    color: Uniform<C>,
    alpha: Uniform<T>,
}

#[cfg(feature = "random")]
impl<C, T> SampleUniform for Alpha<C, T>
where
    T: Clone + SampleUniform,
    C: Clone + SampleUniform,
{
    type Sampler = UniformAlpha<C, T>;
}

#[cfg(feature = "random")]
impl<C, T> UniformSampler for UniformAlpha<C, T>
where
    T: Clone + SampleUniform,
    C: Clone + SampleUniform,
{
    type X = Alpha<C, T>;

    fn new<B1, B2>(low_b: B1, high_b: B2) -> Self
    where
        B1: SampleBorrow<Self::X> + Sized,
        B2: SampleBorrow<Self::X> + Sized,
    {
        let low = low_b.borrow().clone();
        let high = high_b.borrow().clone();

        UniformAlpha {
            color: Uniform::new::<C, _>(low.color, high.color),
            alpha: Uniform::new::<_, T>(low.alpha, high.alpha),
        }
    }

    fn new_inclusive<B1, B2>(low_b: B1, high_b: B2) -> Self
    where
        B1: SampleBorrow<Self::X> + Sized,
        B2: SampleBorrow<Self::X> + Sized,
    {
        let low = low_b.borrow().clone();
        let high = high_b.borrow().clone();

        UniformAlpha {
            color: Uniform::new_inclusive::<C, _>(low.color, high.color),
            alpha: Uniform::new_inclusive::<_, T>(low.alpha, high.alpha),
        }
    }

    fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> Alpha<C, T> {
        Alpha {
            color: self.color.sample(rng),
            alpha: self.alpha.sample(rng),
        }
    }
}

#[cfg(feature = "bytemuck")]
unsafe impl<C, T> bytemuck::Zeroable for Alpha<C, T>
where
    C: bytemuck::Zeroable,
    T: bytemuck::Zeroable,
{
}

// Safety:
//
// It is a requirement of `ArrayCast` that the in-memory representation of `C`
// is made of `T`s. Because `T` is `Pod`, `Alpha<C, T>` is `Pod` as well because
// no internal padding can be introduced during monomorphization.
#[cfg(feature = "bytemuck")]
unsafe impl<C, T> bytemuck::Pod for Alpha<C, T>
where
    T: bytemuck::Pod,
    C: bytemuck::Pod + ArrayCast,
{
}

#[cfg(test)]
mod test {
    use crate::encoding::Srgb;
    use crate::rgb::Rgba;

    #[test]
    fn lower_hex() {
        assert_eq!(
            format!("{:x}", Rgba::<Srgb, u8>::new(171, 193, 35, 161)),
            "abc123a1"
        );
    }

    #[test]
    fn lower_hex_small_numbers() {
        assert_eq!(
            format!("{:x}", Rgba::<Srgb, u8>::new(1, 2, 3, 4)),
            "01020304"
        );
        assert_eq!(
            format!("{:x}", Rgba::<Srgb, u16>::new(1, 2, 3, 4)),
            "0001000200030004"
        );
        assert_eq!(
            format!("{:x}", Rgba::<Srgb, u32>::new(1, 2, 3, 4)),
            "00000001000000020000000300000004"
        );
        assert_eq!(
            format!("{:x}", Rgba::<Srgb, u64>::new(1, 2, 3, 4)),
            "0000000000000001000000000000000200000000000000030000000000000004"
        );
    }

    #[test]
    fn lower_hex_custom_width() {
        assert_eq!(
            format!("{:03x}", Rgba::<Srgb, u8>::new(1, 2, 3, 4)),
            "001002003004"
        );
        assert_eq!(
            format!("{:03x}", Rgba::<Srgb, u16>::new(1, 2, 3, 4)),
            "001002003004"
        );
        assert_eq!(
            format!("{:03x}", Rgba::<Srgb, u32>::new(1, 2, 3, 4)),
            "001002003004"
        );
        assert_eq!(
            format!("{:03x}", Rgba::<Srgb, u64>::new(1, 2, 3, 4)),
            "001002003004"
        );
    }

    #[test]
    fn upper_hex() {
        assert_eq!(
            format!("{:X}", Rgba::<Srgb, u8>::new(171, 193, 35, 161)),
            "ABC123A1"
        );
    }

    #[test]
    fn upper_hex_small_numbers() {
        assert_eq!(
            format!("{:X}", Rgba::<Srgb, u8>::new(1, 2, 3, 4)),
            "01020304"
        );
        assert_eq!(
            format!("{:X}", Rgba::<Srgb, u16>::new(1, 2, 3, 4)),
            "0001000200030004"
        );
        assert_eq!(
            format!("{:X}", Rgba::<Srgb, u32>::new(1, 2, 3, 4)),
            "00000001000000020000000300000004"
        );
        assert_eq!(
            format!("{:X}", Rgba::<Srgb, u64>::new(1, 2, 3, 4)),
            "0000000000000001000000000000000200000000000000030000000000000004"
        );
    }

    #[test]
    fn upper_hex_custom_width() {
        assert_eq!(
            format!("{:03X}", Rgba::<Srgb, u8>::new(1, 2, 3, 4)),
            "001002003004"
        );
        assert_eq!(
            format!("{:03X}", Rgba::<Srgb, u16>::new(1, 2, 3, 4)),
            "001002003004"
        );
        assert_eq!(
            format!("{:03X}", Rgba::<Srgb, u32>::new(1, 2, 3, 4)),
            "001002003004"
        );
        assert_eq!(
            format!("{:03X}", Rgba::<Srgb, u64>::new(1, 2, 3, 4)),
            "001002003004"
        );
    }

    #[test]
    fn check_min_max_components() {
        assert_eq!(Rgba::<Srgb>::min_alpha(), 0.0);
        assert_eq!(Rgba::<Srgb>::max_alpha(), 1.0);
    }

    #[cfg(feature = "serializing")]
    #[test]
    fn serialize() {
        let color = Rgba::<Srgb>::new(0.3, 0.8, 0.1, 0.5);

        assert_eq!(
            serde_json::to_string(&color).unwrap(),
            r#"{"red":0.3,"green":0.8,"blue":0.1,"alpha":0.5}"#
        );

        assert_eq!(
            ron::to_string(&color).unwrap(),
            r#"(red:0.3,green:0.8,blue:0.1,alpha:0.5)"#
        );
    }

    #[cfg(feature = "serializing")]
    #[test]
    fn deserialize() {
        let color = Rgba::<Srgb>::new(0.3, 0.8, 0.1, 0.5);

        assert_eq!(
            serde_json::from_str::<Rgba<Srgb>>(r#"{"alpha":0.5,"red":0.3,"green":0.8,"blue":0.1}"#)
                .unwrap(),
            color
        );

        assert_eq!(
            ron::from_str::<Rgba<Srgb>>(r#"(alpha:0.5,red:0.3,green:0.8,blue:0.1)"#).unwrap(),
            color
        );

        assert_eq!(
            ron::from_str::<Rgba<Srgb>>(r#"Rgb(alpha:0.5,red:0.3,green:0.8,blue:0.1)"#).unwrap(),
            color
        );
    }

    #[cfg(feature = "serializing")]
    #[test]
    fn serde_round_trips() {
        let color = Rgba::<Srgb>::new(0.3, 0.8, 0.1, 0.5);

        assert_eq!(
            serde_json::from_str::<Rgba<Srgb>>(&serde_json::to_string(&color).unwrap()).unwrap(),
            color
        );

        assert_eq!(
            ron::from_str::<Rgba<Srgb>>(&ron::to_string(&color).unwrap()).unwrap(),
            color
        );
    }

    #[cfg(feature = "serializing")]
    #[test]
    fn serde_various_types() {
        macro_rules! test_roundtrip {
            ($value:expr $(, $ron_name:expr)?) => {
                let value = super::Alpha {
                    color: $value,
                    alpha: 0.5,
                };
                assert_eq!(
                    serde_json::from_str::<super::Alpha<_, f32>>(
                        &serde_json::to_string(&value).expect("json serialization")
                    )
                    .expect("json deserialization"),
                    value
                );

                let ron_string = ron::to_string(&value).expect("ron serialization");
                assert_eq!(
                    ron::from_str::<super::Alpha<_, f32>>(&ron_string)
                        .expect("ron deserialization"),
                    value
                );
                $(
                    assert_eq!(
                        ron::from_str::<super::Alpha<_, f32>>(&format!("{}{ron_string}", $ron_name))
                            .expect("ron deserialization"),
                        value
                    );
                )?
            };
        }

        #[derive(Serialize, Deserialize, PartialEq, Debug)]
        struct Empty;
        #[derive(Serialize, Deserialize, PartialEq, Debug)]
        struct UnitTuple();
        #[derive(Serialize, Deserialize, PartialEq, Debug)]
        struct Newtype(f32);
        #[derive(Serialize, Deserialize, PartialEq, Debug)]
        struct Tuple(f32, f32);
        #[derive(Serialize, Deserialize, PartialEq, Debug)]
        struct Struct {
            value: f32,
        }

        test_roundtrip!(());
        test_roundtrip!(Empty, "Empty");
        test_roundtrip!(UnitTuple(), "UnitTuple");
        test_roundtrip!(Newtype(0.1), "Newtype");
        test_roundtrip!(Tuple(0.1, 0.2), "Tuple");
        test_roundtrip!(Struct { value: 0.1 }, "Struct");
    }

    test_uniform_distribution! {
        Rgba<Srgb, f32> {
            red: (0.0, 1.0),
            green: (0.0, 1.0),
            blue: (0.0, 1.0),
            alpha: (0.0, 1.0)
        },
        min: Rgba::new(0.0f32, 0.0, 0.0, 0.0),
        max: Rgba::new(1.0, 1.0, 1.0, 1.0)
    }
}