1 files changed, 153 insertions, 0 deletions
diff --git a/crates/typst-library/src/layout/ratio.rs b/crates/typst-library/src/layout/ratio.rs
new file mode 100644
index 00000000..1c0dcd29
--- /dev/null
+++ b/crates/typst-library/src/layout/ratio.rs
@@ -0,0 +1,153 @@
+use std::fmt::{self, Debug, Formatter};
+use std::ops::{Add, Div, Mul, Neg};
+
+use ecow::EcoString;
+use typst_utils::{Numeric, Scalar};
+
+use crate::foundations::{repr, ty, Repr};
+
+/// A ratio of a whole.
+///
+/// Written as a number, followed by a percent sign.
+///
+/// # Example
+/// ```example
+/// #set align(center)
+/// #scale(x: 150%)[
+///   Scaled apart.
+/// ]
+/// ```
+#[ty(cast)]
+#[derive(Default, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
+pub struct Ratio(Scalar);
+
+impl Ratio {
+    /// A ratio of `0%` represented as `0.0`.
+    pub const fn zero() -> Self {
+        Self(Scalar::ZERO)
+    }
+
+    /// A ratio of `100%` represented as `1.0`.
+    pub const fn one() -> Self {
+        Self(Scalar::ONE)
+    }
+
+    /// Create a new ratio from a value, where `1.0` means `100%`.
+    pub const fn new(ratio: f64) -> Self {
+        Self(Scalar::new(ratio))
+    }
+
+    /// Get the underlying ratio.
+    pub const fn get(self) -> f64 {
+        (self.0).get()
+    }
+
+    /// Whether the ratio is zero.
+    pub fn is_zero(self) -> bool {
+        self.0 == 0.0
+    }
+
+    /// Whether the ratio is one.
+    pub fn is_one(self) -> bool {
+        self.0 == 1.0
+    }
+
+    /// The absolute value of this ratio.
+    pub fn abs(self) -> Self {
+        Self::new(self.get().abs())
+    }
+
+    /// Return the ratio of the given `whole`.
+    pub fn of<T: Numeric>(self, whole: T) -> T {
+        let resolved = whole * self.get();
+        if resolved.is_finite() {
+            resolved
+        } else {
+            T::zero()
+        }
+    }
+}
+
+impl Debug for Ratio {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        write!(f, "{:?}%", self.get() * 100.0)
+    }
+}
+
+impl Repr for Ratio {
+    fn repr(&self) -> EcoString {
+        repr::format_float_with_unit(self.get() * 100.0, "%")
+    }
+}
+
+impl Neg for Ratio {
+    type Output = Self;
+
+    fn neg(self) -> Self {
+        Self(-self.0)
+    }
+}
+
+impl Add for Ratio {
+    type Output = Self;
+
+    fn add(self, other: Self) -> Self {
+        Self(self.0 + other.0)
+    }
+}
+
+typst_utils::sub_impl!(Ratio - Ratio -> Ratio);
+
+impl Mul for Ratio {
+    type Output = Self;
+
+    fn mul(self, other: Self) -> Self {
+        Self(self.0 * other.0)
+    }
+}
+
+impl Mul<f64> for Ratio {
+    type Output = Self;
+
+    fn mul(self, other: f64) -> Self {
+        Self(self.0 * other)
+    }
+}
+
+impl Mul<Ratio> for f64 {
+    type Output = Ratio;
+
+    fn mul(self, other: Ratio) -> Ratio {
+        other * self
+    }
+}
+
+impl Div for Ratio {
+    type Output = f64;
+
+    fn div(self, other: Self) -> f64 {
+        self.get() / other.get()
+    }
+}
+
+impl Div<f64> for Ratio {
+    type Output = Self;
+
+    fn div(self, other: f64) -> Self {
+        Self(self.0 / other)
+    }
+}
+
+impl Div<Ratio> for f64 {
+    type Output = Self;
+
+    fn div(self, other: Ratio) -> Self {
+        self / other.get()
+    }
+}
+
+typst_utils::assign_impl!(Ratio += Ratio);
+typst_utils::assign_impl!(Ratio -= Ratio);
+typst_utils::assign_impl!(Ratio *= Ratio);
+typst_utils::assign_impl!(Ratio *= f64);
+typst_utils::assign_impl!(Ratio /= f64);