gpui/

lerp.rs

//! Interpolation between two values of the same type.
use crate::{
    AbsoluteLength, Background, Bounds, Corners, DefiniteLength, DevicePixels, Edges, Fill, Length,
    Percentage, Pixels, Point, Radians, Relative, Rems, RingColor, Size, colors::Colors,
};
use palette::{
    Hsla, IntoColor, Oklab, Oklaba,
    rgb::{Rgb, Rgba},
};
use std::{
    fmt::Debug,
    ops::{Add, Mul, Sub},
};

/// A type whose values can be interpolated between two endpoints.
///
/// `delta` is the fraction of the way from `self` to `to`. `0.0` gives `self`, and `1.0` gives
/// `to`. For numbers, deltas outside that range extrapolate. [`Animated`](crate::Animated),
/// [`Transition`](crate::Transition) and style transitions call `lerp` for every frame.
///
/// Types that cannot be meaningfully blended, such as a gradient [`Background`](crate::Background)
/// or a length that mixes pixels with rems, hold `self` until `delta` reaches `1.0`, then switch to
/// `to`. [`Hsla`](crate::Hsla) values are converted through RGB; [`Interpolate`](crate::Interpolate)
/// instead takes the shorter path around the hue wheel.
///
/// # Examples
///
/// ```
/// use gpui::{Lerp, px};
///
/// assert_eq!(0.0_f32.lerp(&10.0, 0.25), 2.5);
/// assert_eq!(px(0.).lerp(&px(10.), 0.5), px(5.));
///
/// // A bool blends to a number.
/// let halfway: f32 = false.lerp(&true, 0.5);
/// assert_eq!(halfway, 0.5);
/// ```
pub trait Lerp<Output = Self>
where
    Self: Sized,
{
    /// Returns the value `delta` of the way from `self` to `to`.
    fn lerp(&self, to: &Self, delta: f32) -> Output;
}

impl Lerp<f32> for bool {
    fn lerp(&self, to: &Self, delta: f32) -> f32 {
        lerp(*self as u8 as f32, *to as u8 as f32, delta)
    }
}

macro_rules! float_lerps {
    ( $( $ty:ty ),+ ) => {
        $(
            impl Lerp for $ty {
                fn lerp(&self, to: &Self, delta: f32) -> Self {
                    lerp(*self, *to, delta as $ty)
                }
            }
        )+
    };
}

float_lerps!(f32, f64);

macro_rules! int_lerps {
    ( $( $ty:ident as $ty_into:ident ),+ ) => {
        $(
            impl Lerp for $ty {
                fn lerp(&self, to: &Self, delta: f32) -> Self {
                    lerp(*self as $ty_into, *to as $ty_into, delta as $ty_into) as $ty
                }
            }
        )+
    };
}

int_lerps!(
    usize as f32,
    u8 as f32,
    u16 as f32,
    u32 as f32,
    u64 as f64,
    u128 as f64,
    isize as f32,
    i8 as f32,
    i16 as f32,
    i32 as f32,
    i64 as f64,
    i128 as f64
);

macro_rules! struct_lerps {
    ( $( $ty:ident $( < $gen:ident > )? { $( $n:ident ),+ } ),+ $(,)? ) => {
        $(
            impl$(<$gen: Lerp + Clone + Debug + Default + PartialEq>)? Lerp for $ty$(<$gen>)? {
                fn lerp(&self, to: &Self, delta: f32) -> Self {
                    $ty$(::<$gen>)? {
                        $(
                            $n: self.$n.lerp(&to.$n, delta)
                        ),+
                    }
                }
            }
        )+
    };
}

struct_lerps!(
    Point<T> { x, y },
    Size<T> { width, height },
    Edges<T> { top, right, bottom, left },
    Corners<T> { top_left, top_right, bottom_right, bottom_left },
    Bounds<T> { origin, size },
    Rgba { color, alpha },
    Colors { text, selected_text, background, disabled, selected, border, separator, container }
);

macro_rules! tuple_struct_lerps {
    ( $( $ty:ident ( $n:ty ) ),+ ) => {
        $(
            impl Lerp for $ty {
                fn lerp(&self, to: &Self, delta: f32) -> Self {
                    $ty(self.0.lerp(&to.0, delta))
                }
            }
        )+
    };
}

tuple_struct_lerps!(
    Radians(f32),
    Percentage(f32),
    DevicePixels(i32),
    Relative(f32),
    Rems(f32),
    Pixels(f32)
);

macro_rules! new_constructor_lerps {
    ( $( $ty:ident $( < $gen:ident > )? ::new ( $( $n:ident ),+ ) ),+ $(,)? ) => {
        $(
            impl$(<$gen: Lerp + Clone + Debug + Default + PartialEq>)? Lerp for $ty$(<$gen>)? {
                fn lerp(&self, to: &Self, delta: f32) -> Self {
                    $ty$(::<$gen>)?::new(
                        $(
                            self.$n.lerp(&to.$n, delta)
                        ),+
                    )
                }
            }
        )+
    };
}

new_constructor_lerps!(
    Rgb::new(red, green, blue),
    Oklab::new(l, a, b),
    Oklaba::new(l, a, b, alpha)
);

impl Lerp for Hsla {
    fn lerp(&self, to: &Self, delta: f32) -> Self {
        if delta <= 0.0 {
            return *self;
        }
        if delta >= 1.0 {
            return *to;
        }

        let from: Rgba = (*self).into_color();
        let to: Rgba = (*to).into_color();
        from.lerp(&to, delta).into_color()
    }
}

impl Lerp for RingColor {
    fn lerp(&self, to: &Self, delta: f32) -> Self {
        match (*self, *to) {
            (Self::Color(from), Self::Color(to)) => Self::Color(from.lerp(&to, delta)),
            (_, to) if delta >= 1.0 => to,
            (from, _) => from,
        }
    }
}

impl Lerp for AbsoluteLength {
    fn lerp(&self, to: &Self, delta: f32) -> Self {
        match (*self, *to) {
            (Self::Pixels(from), Self::Pixels(to)) => Self::Pixels(from.lerp(&to, delta)),
            (Self::Rems(from), Self::Rems(to)) => Self::Rems(from.lerp(&to, delta)),
            (from, Self::Pixels(to)) if from.is_zero() => {
                Self::Pixels(Pixels::default().lerp(&to, delta))
            }
            (from, Self::Rems(to)) if from.is_zero() => {
                Self::Rems(Rems::default().lerp(&to, delta))
            }
            (Self::Pixels(from), to) if to.is_zero() => {
                Self::Pixels(from.lerp(&Pixels::default(), delta))
            }
            (Self::Rems(from), to) if to.is_zero() => {
                Self::Rems(from.lerp(&Rems::default(), delta))
            }
            _ if delta >= 1.0 => *to,
            _ => *self,
        }
    }
}

impl Lerp for DefiniteLength {
    fn lerp(&self, to: &Self, delta: f32) -> Self {
        match (*self, *to) {
            (Self::Absolute(from), Self::Absolute(to)) => Self::Absolute(from.lerp(&to, delta)),
            (Self::Relative(from), Self::Relative(to)) => Self::Relative(from.lerp(&to, delta)),
            _ if delta >= 1.0 => *to,
            _ => *self,
        }
    }
}

impl Lerp for Length {
    fn lerp(&self, to: &Self, delta: f32) -> Self {
        match (*self, *to) {
            (Self::Definite(from), Self::Definite(to)) => Self::Definite(from.lerp(&to, delta)),
            _ if delta >= 1.0 => *to,
            _ => *self,
        }
    }
}

impl Lerp for Background {
    fn lerp(&self, to: &Self, delta: f32) -> Self {
        if delta <= 0.0 {
            return *self;
        }
        if delta >= 1.0 {
            return *to;
        }

        match (self.as_solid(), to.as_solid()) {
            (Some(from), Some(to_color)) => {
                Background::from(from.lerp(&to_color, delta)).color_space(to.interpolation_space())
            }
            _ => *self,
        }
    }
}

impl Lerp for Fill {
    fn lerp(&self, to: &Self, delta: f32) -> Self {
        match (self, to) {
            (Self::Color(from), Self::Color(to)) => Self::Color(from.lerp(to, delta)),
        }
    }
}

fn lerp<T>(from: T, to: T, alpha: T) -> T
where
    T: Copy + Add<Output = T> + Sub<Output = T> + Mul<Output = T>,
{
    from + (to - from) * alpha
}