Split dpi module out into a separate crate (#3518)

Co-authored-by: John Nunley <dev@notgull.net>

dpi/src/lib.rs

@@ -0,0 +1,939 @@
+//! # DPI
+//!
+//! ## Why should I care about UI scaling?
+//!
+//! Modern computer screens don't have a consistent relationship between resolution and size.
+//! 1920x1080 is a common resolution for both desktop and mobile screens, despite mobile screens
+//! typically being less than a quarter the size of their desktop counterparts. Moreover, neither
+//! desktop nor mobile screens have consistent resolutions within their own size classes - common
+//! mobile screens range from below 720p to above 1440p, and desktop screens range from 720p to 5K
+//! and beyond.
+//!
+//! Given that, it's a mistake to assume that 2D content will only be displayed on screens with
+//! a consistent pixel density. If you were to render a 96-pixel-square image on a 1080p screen and
+//! then render the same image on a similarly-sized 4K screen, the 4K rendition would only take up
+//! about a quarter of the physical space as it did on the 1080p screen. That issue is especially
+//! problematic with text rendering, where quarter-sized text becomes a significant legibility
+//! problem.
+//!
+//! Failure to account for the scale factor can create a significantly degraded user experience.
+//! Most notably, it can make users feel like they have bad eyesight, which will potentially cause
+//! them to think about growing elderly, resulting in them having an existential crisis. Once users
+//! enter that state, they will no longer be focused on your application.
+//!
+//! ## How should I handle it?
+//!
+//! The solution to this problem is to account for the device's *scale factor*. The scale factor is
+//! the factor UI elements should be scaled by to be consistent with the rest of the user's system -
+//! for example, a button that's usually 50 pixels across would be 100 pixels across on a device
+//! with a scale factor of `2.0`, or 75 pixels across with a scale factor of `1.5`.
+//!
+//! Many UI systems, such as CSS, expose DPI-dependent units like [points] or [picas]. That's
+//! usually a mistake since there's no consistent mapping between the scale factor and the screen's
+//! actual DPI. Unless printing to a physical medium, you should work in scaled pixels rather
+//! than any DPI-dependent units.
+//!
+//! ### Position and Size types
+//!
+//! The [`PhysicalPosition`] / [`PhysicalSize`] types correspond with the actual pixels on the
+//! device, and the [`LogicalPosition`] / [`LogicalSize`] types correspond to the physical pixels
+//! divided by the scale factor.
+//!
+//! The position and size types are generic over their exact pixel type, `P`, to allow the
+//! API to have integer precision where appropriate (e.g. most window manipulation functions) and
+//! floating precision when necessary (e.g. logical sizes for fractional scale factors and touch
+//! input). If `P` is a floating-point type, please do not cast the values with `as {int}`. Doing so
+//! will truncate the fractional part of the float rather than properly round to the nearest
+//! integer. Use the provided `cast` function or [`From`]/[`Into`] conversions, which handle the
+//! rounding properly. Note that precision loss will still occur when rounding from a float to an
+//! int, although rounding lessens the problem.
+//!
+//! ## Cargo Features
+//!
+//! This crate provides the following Cargo features:
+//!
+//! * `serde`: Enables serialization/deserialization of certain types with
+//!   [Serde](https://crates.io/crates/serde).
+//! * `mint`: Enables mint (math interoperability standard types) conversions.
+//!
+//!
+//! [points]: https://en.wikipedia.org/wiki/Point_(typography)
+//! [picas]: https://en.wikipedia.org/wiki/Pica_(typography)
+
+#![cfg_attr(
+    docsrs,
+    feature(doc_auto_cfg, doc_cfg_hide),
+    doc(cfg_hide(doc, docsrs))
+)]
+#![forbid(unsafe_code)]
+
+#[cfg(feature = "serde")]
+use serde::{Deserialize, Serialize};
+
+pub trait Pixel: Copy + Into<f64> {
+    fn from_f64(f: f64) -> Self;
+    fn cast<P: Pixel>(self) -> P {
+        P::from_f64(self.into())
+    }
+}
+
+impl Pixel for u8 {
+    fn from_f64(f: f64) -> Self {
+        f.round() as u8
+    }
+}
+impl Pixel for u16 {
+    fn from_f64(f: f64) -> Self {
+        f.round() as u16
+    }
+}
+impl Pixel for u32 {
+    fn from_f64(f: f64) -> Self {
+        f.round() as u32
+    }
+}
+impl Pixel for i8 {
+    fn from_f64(f: f64) -> Self {
+        f.round() as i8
+    }
+}
+impl Pixel for i16 {
+    fn from_f64(f: f64) -> Self {
+        f.round() as i16
+    }
+}
+impl Pixel for i32 {
+    fn from_f64(f: f64) -> Self {
+        f.round() as i32
+    }
+}
+impl Pixel for f32 {
+    fn from_f64(f: f64) -> Self {
+        f as f32
+    }
+}
+impl Pixel for f64 {
+    fn from_f64(f: f64) -> Self {
+        f
+    }
+}
+
+/// Checks that the scale factor is a normal positive `f64`.
+///
+/// All functions that take a scale factor assert that this will return `true`. If you're sourcing scale factors from
+/// anywhere other than winit, it's recommended to validate them using this function before passing them to winit;
+/// otherwise, you risk panics.
+#[inline]
+pub fn validate_scale_factor(scale_factor: f64) -> bool {
+    scale_factor.is_sign_positive() && scale_factor.is_normal()
+}
+
+/// A position represented in logical pixels.
+///
+/// The position is stored as floats, so please be careful. Casting floats to integers truncates the
+/// fractional part, which can cause noticeable issues. To help with that, an `Into<(i32, i32)>`
+/// implementation is provided which does the rounding for you.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Default, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub struct LogicalPosition<P> {
+    pub x: P,
+    pub y: P,
+}
+
+impl<P> LogicalPosition<P> {
+    #[inline]
+    pub const fn new(x: P, y: P) -> Self {
+        LogicalPosition { x, y }
+    }
+}
+
+impl<P: Pixel> LogicalPosition<P> {
+    #[inline]
+    pub fn from_physical<T: Into<PhysicalPosition<X>>, X: Pixel>(
+        physical: T,
+        scale_factor: f64,
+    ) -> Self {
+        physical.into().to_logical(scale_factor)
+    }
+
+    #[inline]
+    pub fn to_physical<X: Pixel>(&self, scale_factor: f64) -> PhysicalPosition<X> {
+        assert!(validate_scale_factor(scale_factor));
+        let x = self.x.into() * scale_factor;
+        let y = self.y.into() * scale_factor;
+        PhysicalPosition::new(x, y).cast()
+    }
+
+    #[inline]
+    pub fn cast<X: Pixel>(&self) -> LogicalPosition<X> {
+        LogicalPosition {
+            x: self.x.cast(),
+            y: self.y.cast(),
+        }
+    }
+}
+
+impl<P: Pixel, X: Pixel> From<(X, X)> for LogicalPosition<P> {
+    fn from((x, y): (X, X)) -> LogicalPosition<P> {
+        LogicalPosition::new(x.cast(), y.cast())
+    }
+}
+
+impl<P: Pixel, X: Pixel> From<LogicalPosition<P>> for (X, X) {
+    fn from(p: LogicalPosition<P>) -> (X, X) {
+        (p.x.cast(), p.y.cast())
+    }
+}
+
+impl<P: Pixel, X: Pixel> From<[X; 2]> for LogicalPosition<P> {
+    fn from([x, y]: [X; 2]) -> LogicalPosition<P> {
+        LogicalPosition::new(x.cast(), y.cast())
+    }
+}
+
+impl<P: Pixel, X: Pixel> From<LogicalPosition<P>> for [X; 2] {
+    fn from(p: LogicalPosition<P>) -> [X; 2] {
+        [p.x.cast(), p.y.cast()]
+    }
+}
+
+#[cfg(feature = "mint")]
+impl<P: Pixel> From<mint::Point2<P>> for LogicalPosition<P> {
+    fn from(p: mint::Point2<P>) -> Self {
+        Self::new(p.x, p.y)
+    }
+}
+
+#[cfg(feature = "mint")]
+impl<P: Pixel> From<LogicalPosition<P>> for mint::Point2<P> {
+    fn from(p: LogicalPosition<P>) -> Self {
+        mint::Point2 { x: p.x, y: p.y }
+    }
+}
+
+/// A position represented in physical pixels.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Default, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub struct PhysicalPosition<P> {
+    pub x: P,
+    pub y: P,
+}
+
+impl<P> PhysicalPosition<P> {
+    #[inline]
+    pub const fn new(x: P, y: P) -> Self {
+        PhysicalPosition { x, y }
+    }
+}
+
+impl<P: Pixel> PhysicalPosition<P> {
+    #[inline]
+    pub fn from_logical<T: Into<LogicalPosition<X>>, X: Pixel>(
+        logical: T,
+        scale_factor: f64,
+    ) -> Self {
+        logical.into().to_physical(scale_factor)
+    }
+
+    #[inline]
+    pub fn to_logical<X: Pixel>(&self, scale_factor: f64) -> LogicalPosition<X> {
+        assert!(validate_scale_factor(scale_factor));
+        let x = self.x.into() / scale_factor;
+        let y = self.y.into() / scale_factor;
+        LogicalPosition::new(x, y).cast()
+    }
+
+    #[inline]
+    pub fn cast<X: Pixel>(&self) -> PhysicalPosition<X> {
+        PhysicalPosition {
+            x: self.x.cast(),
+            y: self.y.cast(),
+        }
+    }
+}
+
+impl<P: Pixel, X: Pixel> From<(X, X)> for PhysicalPosition<P> {
+    fn from((x, y): (X, X)) -> PhysicalPosition<P> {
+        PhysicalPosition::new(x.cast(), y.cast())
+    }
+}
+
+impl<P: Pixel, X: Pixel> From<PhysicalPosition<P>> for (X, X) {
+    fn from(p: PhysicalPosition<P>) -> (X, X) {
+        (p.x.cast(), p.y.cast())
+    }
+}
+
+impl<P: Pixel, X: Pixel> From<[X; 2]> for PhysicalPosition<P> {
+    fn from([x, y]: [X; 2]) -> PhysicalPosition<P> {
+        PhysicalPosition::new(x.cast(), y.cast())
+    }
+}
+
+impl<P: Pixel, X: Pixel> From<PhysicalPosition<P>> for [X; 2] {
+    fn from(p: PhysicalPosition<P>) -> [X; 2] {
+        [p.x.cast(), p.y.cast()]
+    }
+}
+
+#[cfg(feature = "mint")]
+impl<P: Pixel> From<mint::Point2<P>> for PhysicalPosition<P> {
+    fn from(p: mint::Point2<P>) -> Self {
+        Self::new(p.x, p.y)
+    }
+}
+
+#[cfg(feature = "mint")]
+impl<P: Pixel> From<PhysicalPosition<P>> for mint::Point2<P> {
+    fn from(p: PhysicalPosition<P>) -> Self {
+        mint::Point2 { x: p.x, y: p.y }
+    }
+}
+
+/// A size represented in logical pixels.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Default, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub struct LogicalSize<P> {
+    pub width: P,
+    pub height: P,
+}
+
+impl<P> LogicalSize<P> {
+    #[inline]
+    pub const fn new(width: P, height: P) -> Self {
+        LogicalSize { width, height }
+    }
+}
+
+impl<P: Pixel> LogicalSize<P> {
+    #[inline]
+    pub fn from_physical<T: Into<PhysicalSize<X>>, X: Pixel>(
+        physical: T,
+        scale_factor: f64,
+    ) -> Self {
+        physical.into().to_logical(scale_factor)
+    }
+
+    #[inline]
+    pub fn to_physical<X: Pixel>(&self, scale_factor: f64) -> PhysicalSize<X> {
+        assert!(validate_scale_factor(scale_factor));
+        let width = self.width.into() * scale_factor;
+        let height = self.height.into() * scale_factor;
+        PhysicalSize::new(width, height).cast()
+    }
+
+    #[inline]
+    pub fn cast<X: Pixel>(&self) -> LogicalSize<X> {
+        LogicalSize {
+            width: self.width.cast(),
+            height: self.height.cast(),
+        }
+    }
+}
+
+impl<P: Pixel, X: Pixel> From<(X, X)> for LogicalSize<P> {
+    fn from((x, y): (X, X)) -> LogicalSize<P> {
+        LogicalSize::new(x.cast(), y.cast())
+    }
+}
+
+impl<P: Pixel, X: Pixel> From<LogicalSize<P>> for (X, X) {
+    fn from(s: LogicalSize<P>) -> (X, X) {
+        (s.width.cast(), s.height.cast())
+    }
+}
+
+impl<P: Pixel, X: Pixel> From<[X; 2]> for LogicalSize<P> {
+    fn from([x, y]: [X; 2]) -> LogicalSize<P> {
+        LogicalSize::new(x.cast(), y.cast())
+    }
+}
+
+impl<P: Pixel, X: Pixel> From<LogicalSize<P>> for [X; 2] {
+    fn from(s: LogicalSize<P>) -> [X; 2] {
+        [s.width.cast(), s.height.cast()]
+    }
+}
+
+#[cfg(feature = "mint")]
+impl<P: Pixel> From<mint::Vector2<P>> for LogicalSize<P> {
+    fn from(v: mint::Vector2<P>) -> Self {
+        Self::new(v.x, v.y)
+    }
+}
+
+#[cfg(feature = "mint")]
+impl<P: Pixel> From<LogicalSize<P>> for mint::Vector2<P> {
+    fn from(s: LogicalSize<P>) -> Self {
+        mint::Vector2 {
+            x: s.width,
+            y: s.height,
+        }
+    }
+}
+
+/// A size represented in physical pixels.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Default, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub struct PhysicalSize<P> {
+    pub width: P,
+    pub height: P,
+}
+
+impl<P> PhysicalSize<P> {
+    #[inline]
+    pub const fn new(width: P, height: P) -> Self {
+        PhysicalSize { width, height }
+    }
+}
+
+impl<P: Pixel> PhysicalSize<P> {
+    #[inline]
+    pub fn from_logical<T: Into<LogicalSize<X>>, X: Pixel>(logical: T, scale_factor: f64) -> Self {
+        logical.into().to_physical(scale_factor)
+    }
+
+    #[inline]
+    pub fn to_logical<X: Pixel>(&self, scale_factor: f64) -> LogicalSize<X> {
+        assert!(validate_scale_factor(scale_factor));
+        let width = self.width.into() / scale_factor;
+        let height = self.height.into() / scale_factor;
+        LogicalSize::new(width, height).cast()
+    }
+
+    #[inline]
+    pub fn cast<X: Pixel>(&self) -> PhysicalSize<X> {
+        PhysicalSize {
+            width: self.width.cast(),
+            height: self.height.cast(),
+        }
+    }
+}
+
+impl<P: Pixel, X: Pixel> From<(X, X)> for PhysicalSize<P> {
+    fn from((x, y): (X, X)) -> PhysicalSize<P> {
+        PhysicalSize::new(x.cast(), y.cast())
+    }
+}
+
+impl<P: Pixel, X: Pixel> From<PhysicalSize<P>> for (X, X) {
+    fn from(s: PhysicalSize<P>) -> (X, X) {
+        (s.width.cast(), s.height.cast())
+    }
+}
+
+impl<P: Pixel, X: Pixel> From<[X; 2]> for PhysicalSize<P> {
+    fn from([x, y]: [X; 2]) -> PhysicalSize<P> {
+        PhysicalSize::new(x.cast(), y.cast())
+    }
+}
+
+impl<P: Pixel, X: Pixel> From<PhysicalSize<P>> for [X; 2] {
+    fn from(s: PhysicalSize<P>) -> [X; 2] {
+        [s.width.cast(), s.height.cast()]
+    }
+}
+
+#[cfg(feature = "mint")]
+impl<P: Pixel> From<mint::Vector2<P>> for PhysicalSize<P> {
+    fn from(v: mint::Vector2<P>) -> Self {
+        Self::new(v.x, v.y)
+    }
+}
+
+#[cfg(feature = "mint")]
+impl<P: Pixel> From<PhysicalSize<P>> for mint::Vector2<P> {
+    fn from(s: PhysicalSize<P>) -> Self {
+        mint::Vector2 {
+            x: s.width,
+            y: s.height,
+        }
+    }
+}
+
+/// A size that's either physical or logical.
+#[derive(Debug, Copy, Clone, PartialEq)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub enum Size {
+    Physical(PhysicalSize<u32>),
+    Logical(LogicalSize<f64>),
+}
+
+impl Size {
+    pub fn new<S: Into<Size>>(size: S) -> Size {
+        size.into()
+    }
+
+    pub fn to_logical<P: Pixel>(&self, scale_factor: f64) -> LogicalSize<P> {
+        match *self {
+            Size::Physical(size) => size.to_logical(scale_factor),
+            Size::Logical(size) => size.cast(),
+        }
+    }
+
+    pub fn to_physical<P: Pixel>(&self, scale_factor: f64) -> PhysicalSize<P> {
+        match *self {
+            Size::Physical(size) => size.cast(),
+            Size::Logical(size) => size.to_physical(scale_factor),
+        }
+    }
+
+    pub fn clamp<S: Into<Size>>(input: S, min: S, max: S, scale_factor: f64) -> Size {
+        let (input, min, max) = (
+            input.into().to_physical::<f64>(scale_factor),
+            min.into().to_physical::<f64>(scale_factor),
+            max.into().to_physical::<f64>(scale_factor),
+        );
+
+        let width = input.width.clamp(min.width, max.width);
+        let height = input.height.clamp(min.height, max.height);
+
+        PhysicalSize::new(width, height).into()
+    }
+}
+
+impl<P: Pixel> From<PhysicalSize<P>> for Size {
+    #[inline]
+    fn from(size: PhysicalSize<P>) -> Size {
+        Size::Physical(size.cast())
+    }
+}
+
+impl<P: Pixel> From<LogicalSize<P>> for Size {
+    #[inline]
+    fn from(size: LogicalSize<P>) -> Size {
+        Size::Logical(size.cast())
+    }
+}
+
+/// A position that's either physical or logical.
+#[derive(Debug, Copy, Clone, PartialEq)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub enum Position {
+    Physical(PhysicalPosition<i32>),
+    Logical(LogicalPosition<f64>),
+}
+
+impl Position {
+    pub fn new<S: Into<Position>>(position: S) -> Position {
+        position.into()
+    }
+
+    pub fn to_logical<P: Pixel>(&self, scale_factor: f64) -> LogicalPosition<P> {
+        match *self {
+            Position::Physical(position) => position.to_logical(scale_factor),
+            Position::Logical(position) => position.cast(),
+        }
+    }
+
+    pub fn to_physical<P: Pixel>(&self, scale_factor: f64) -> PhysicalPosition<P> {
+        match *self {
+            Position::Physical(position) => position.cast(),
+            Position::Logical(position) => position.to_physical(scale_factor),
+        }
+    }
+}
+
+impl<P: Pixel> From<PhysicalPosition<P>> for Position {
+    #[inline]
+    fn from(position: PhysicalPosition<P>) -> Position {
+        Position::Physical(position.cast())
+    }
+}
+
+impl<P: Pixel> From<LogicalPosition<P>> for Position {
+    #[inline]
+    fn from(position: LogicalPosition<P>) -> Position {
+        Position::Logical(position.cast())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::collections::HashSet;
+
+    macro_rules! test_pixel_int_impl {
+        ($($name:ident => $ty:ty),*) => {$(
+            #[test]
+            fn $name() {
+                assert_eq!(
+                    <$ty as Pixel>::from_f64(37.0),
+                    37,
+                );
+                assert_eq!(
+                    <$ty as Pixel>::from_f64(37.4),
+                    37,
+                );
+                assert_eq!(
+                    <$ty as Pixel>::from_f64(37.5),
+                    38,
+                );
+                assert_eq!(
+                    <$ty as Pixel>::from_f64(37.9),
+                    38,
+                );
+
+                assert_eq!(
+                    <$ty as Pixel>::cast::<u8>(37),
+                    37,
+                );
+                assert_eq!(
+                    <$ty as Pixel>::cast::<u16>(37),
+                    37,
+                );
+                assert_eq!(
+                    <$ty as Pixel>::cast::<u32>(37),
+                    37,
+                );
+                assert_eq!(
+                    <$ty as Pixel>::cast::<i8>(37),
+                    37,
+                );
+                assert_eq!(
+                    <$ty as Pixel>::cast::<i16>(37),
+                    37,
+                );
+                assert_eq!(
+                    <$ty as Pixel>::cast::<i32>(37),
+                    37,
+                );
+            }
+        )*};
+    }
+
+    test_pixel_int_impl! {
+        test_pixel_int_u8 => u8,
+        test_pixel_int_u16 => u16,
+        test_pixel_int_u32 => u32,
+        test_pixel_int_i8 => i8,
+        test_pixel_int_i16 => i16
+    }
+
+    macro_rules! assert_approx_eq {
+        ($a:expr, $b:expr $(,)?) => {
+            assert!(
+                ($a - $b).abs() < 0.001,
+                "{} is not approximately equal to {}",
+                $a,
+                $b
+            );
+        };
+    }
+
+    macro_rules! test_pixel_float_impl {
+    ($($name:ident => $ty:ty),*) => {$(
+        #[test]
+        fn $name() {
+            assert_approx_eq!(
+                <$ty as Pixel>::from_f64(37.0),
+                37.0,
+            );
+            assert_approx_eq!(
+                <$ty as Pixel>::from_f64(37.4),
+                37.4,
+            );
+            assert_approx_eq!(
+                <$ty as Pixel>::from_f64(37.5),
+                37.5,
+            );
+            assert_approx_eq!(
+                <$ty as Pixel>::from_f64(37.9),
+                37.9,
+            );
+
+            assert_eq!(
+                <$ty as Pixel>::cast::<u8>(37.0),
+                37,
+            );
+            assert_eq!(
+                <$ty as Pixel>::cast::<u8>(37.4),
+                37,
+            );
+            assert_eq!(
+                <$ty as Pixel>::cast::<u8>(37.5),
+                38,
+            );
+
+            assert_eq!(
+                <$ty as Pixel>::cast::<u16>(37.0),
+                37,
+            );
+            assert_eq!(
+                <$ty as Pixel>::cast::<u16>(37.4),
+                37,
+            );
+            assert_eq!(
+                <$ty as Pixel>::cast::<u16>(37.5),
+                38,
+            );
+
+            assert_eq!(
+                <$ty as Pixel>::cast::<u32>(37.0),
+                37,
+            );
+            assert_eq!(
+                <$ty as Pixel>::cast::<u32>(37.4),
+                37,
+            );
+            assert_eq!(
+                <$ty as Pixel>::cast::<u32>(37.5),
+                38,
+            );
+
+            assert_eq!(
+                <$ty as Pixel>::cast::<i8>(37.0),
+                37,
+            );
+            assert_eq!(
+                <$ty as Pixel>::cast::<i8>(37.4),
+                37,
+            );
+            assert_eq!(
+                <$ty as Pixel>::cast::<i8>(37.5),
+                38,
+            );
+
+            assert_eq!(
+                <$ty as Pixel>::cast::<i16>(37.0),
+                37,
+            );
+            assert_eq!(
+                <$ty as Pixel>::cast::<i16>(37.4),
+                37,
+            );
+            assert_eq!(
+                <$ty as Pixel>::cast::<i16>(37.5),
+                38,
+            );
+        }
+    )*};
+}
+
+    test_pixel_float_impl! {
+        test_pixel_float_f32 => f32,
+        test_pixel_float_f64 => f64
+    }
+
+    #[test]
+    fn test_validate_scale_factor() {
+        assert!(validate_scale_factor(1.0));
+        assert!(validate_scale_factor(2.0));
+        assert!(validate_scale_factor(3.0));
+        assert!(validate_scale_factor(1.5));
+        assert!(validate_scale_factor(0.5));
+
+        assert!(!validate_scale_factor(0.0));
+        assert!(!validate_scale_factor(-1.0));
+        assert!(!validate_scale_factor(f64::INFINITY));
+        assert!(!validate_scale_factor(f64::NAN));
+        assert!(!validate_scale_factor(f64::NEG_INFINITY));
+    }
+
+    #[test]
+    fn test_logical_position() {
+        let log_pos = LogicalPosition::new(1.0, 2.0);
+        assert_eq!(log_pos.to_physical::<u32>(1.0), PhysicalPosition::new(1, 2));
+        assert_eq!(log_pos.to_physical::<u32>(2.0), PhysicalPosition::new(2, 4));
+        assert_eq!(log_pos.cast::<u32>(), LogicalPosition::new(1, 2));
+        assert_eq!(
+            log_pos,
+            LogicalPosition::from_physical(PhysicalPosition::new(1.0, 2.0), 1.0)
+        );
+        assert_eq!(
+            log_pos,
+            LogicalPosition::from_physical(PhysicalPosition::new(2.0, 4.0), 2.0)
+        );
+        assert_eq!(
+            LogicalPosition::from((2.0, 2.0)),
+            LogicalPosition::new(2.0, 2.0)
+        );
+        assert_eq!(
+            LogicalPosition::from([2.0, 3.0]),
+            LogicalPosition::new(2.0, 3.0)
+        );
+
+        let x: (f64, f64) = log_pos.into();
+        assert_eq!(x, (1.0, 2.0));
+        let x: [f64; 2] = log_pos.into();
+        assert_eq!(x, [1.0, 2.0]);
+    }
+
+    #[test]
+    fn test_physical_position() {
+        assert_eq!(
+            PhysicalPosition::from_logical(LogicalPosition::new(1.0, 2.0), 1.0),
+            PhysicalPosition::new(1, 2)
+        );
+        assert_eq!(
+            PhysicalPosition::from_logical(LogicalPosition::new(2.0, 4.0), 0.5),
+            PhysicalPosition::new(1, 2)
+        );
+        assert_eq!(
+            PhysicalPosition::from((2.0, 2.0)),
+            PhysicalPosition::new(2.0, 2.0)
+        );
+        assert_eq!(
+            PhysicalPosition::from([2.0, 3.0]),
+            PhysicalPosition::new(2.0, 3.0)
+        );
+
+        let x: (f64, f64) = PhysicalPosition::new(1, 2).into();
+        assert_eq!(x, (1.0, 2.0));
+        let x: [f64; 2] = PhysicalPosition::new(1, 2).into();
+        assert_eq!(x, [1.0, 2.0]);
+    }
+
+    #[test]
+    fn test_logical_size() {
+        let log_size = LogicalSize::new(1.0, 2.0);
+        assert_eq!(log_size.to_physical::<u32>(1.0), PhysicalSize::new(1, 2));
+        assert_eq!(log_size.to_physical::<u32>(2.0), PhysicalSize::new(2, 4));
+        assert_eq!(log_size.cast::<u32>(), LogicalSize::new(1, 2));
+        assert_eq!(
+            log_size,
+            LogicalSize::from_physical(PhysicalSize::new(1.0, 2.0), 1.0)
+        );
+        assert_eq!(
+            log_size,
+            LogicalSize::from_physical(PhysicalSize::new(2.0, 4.0), 2.0)
+        );
+        assert_eq!(LogicalSize::from((2.0, 2.0)), LogicalSize::new(2.0, 2.0));
+        assert_eq!(LogicalSize::from([2.0, 3.0]), LogicalSize::new(2.0, 3.0));
+
+        let x: (f64, f64) = log_size.into();
+        assert_eq!(x, (1.0, 2.0));
+        let x: [f64; 2] = log_size.into();
+        assert_eq!(x, [1.0, 2.0]);
+    }
+
+    #[test]
+    fn test_physical_size() {
+        assert_eq!(
+            PhysicalSize::from_logical(LogicalSize::new(1.0, 2.0), 1.0),
+            PhysicalSize::new(1, 2)
+        );
+        assert_eq!(
+            PhysicalSize::from_logical(LogicalSize::new(2.0, 4.0), 0.5),
+            PhysicalSize::new(1, 2)
+        );
+        assert_eq!(PhysicalSize::from((2.0, 2.0)), PhysicalSize::new(2.0, 2.0));
+        assert_eq!(PhysicalSize::from([2.0, 3.0]), PhysicalSize::new(2.0, 3.0));
+
+        let x: (f64, f64) = PhysicalSize::new(1, 2).into();
+        assert_eq!(x, (1.0, 2.0));
+        let x: [f64; 2] = PhysicalSize::new(1, 2).into();
+        assert_eq!(x, [1.0, 2.0]);
+    }
+
+    #[test]
+    fn test_size() {
+        assert_eq!(
+            Size::new(PhysicalSize::new(1, 2)),
+            Size::Physical(PhysicalSize::new(1, 2))
+        );
+        assert_eq!(
+            Size::new(LogicalSize::new(1.0, 2.0)),
+            Size::Logical(LogicalSize::new(1.0, 2.0))
+        );
+
+        assert_eq!(
+            Size::new(PhysicalSize::new(1, 2)).to_logical::<f64>(1.0),
+            LogicalSize::new(1.0, 2.0)
+        );
+        assert_eq!(
+            Size::new(PhysicalSize::new(1, 2)).to_logical::<f64>(2.0),
+            LogicalSize::new(0.5, 1.0)
+        );
+        assert_eq!(
+            Size::new(LogicalSize::new(1.0, 2.0)).to_logical::<f64>(1.0),
+            LogicalSize::new(1.0, 2.0)
+        );
+
+        assert_eq!(
+            Size::new(PhysicalSize::new(1, 2)).to_physical::<u32>(1.0),
+            PhysicalSize::new(1, 2)
+        );
+        assert_eq!(
+            Size::new(PhysicalSize::new(1, 2)).to_physical::<u32>(2.0),
+            PhysicalSize::new(1, 2)
+        );
+        assert_eq!(
+            Size::new(LogicalSize::new(1.0, 2.0)).to_physical::<u32>(1.0),
+            PhysicalSize::new(1, 2)
+        );
+        assert_eq!(
+            Size::new(LogicalSize::new(1.0, 2.0)).to_physical::<u32>(2.0),
+            PhysicalSize::new(2, 4)
+        );
+
+        let small = Size::Physical((1, 2).into());
+        let medium = Size::Logical((3, 4).into());
+        let medium_physical = Size::new(medium.to_physical::<u32>(1.0));
+        let large = Size::Physical((5, 6).into());
+        assert_eq!(Size::clamp(medium, small, large, 1.0), medium_physical);
+        assert_eq!(Size::clamp(small, medium, large, 1.0), medium_physical);
+        assert_eq!(Size::clamp(large, small, medium, 1.0), medium_physical);
+    }
+
+    #[test]
+    fn test_position() {
+        assert_eq!(
+            Position::new(PhysicalPosition::new(1, 2)),
+            Position::Physical(PhysicalPosition::new(1, 2))
+        );
+        assert_eq!(
+            Position::new(LogicalPosition::new(1.0, 2.0)),
+            Position::Logical(LogicalPosition::new(1.0, 2.0))
+        );
+
+        assert_eq!(
+            Position::new(PhysicalPosition::new(1, 2)).to_logical::<f64>(1.0),
+            LogicalPosition::new(1.0, 2.0)
+        );
+        assert_eq!(
+            Position::new(PhysicalPosition::new(1, 2)).to_logical::<f64>(2.0),
+            LogicalPosition::new(0.5, 1.0)
+        );
+        assert_eq!(
+            Position::new(LogicalPosition::new(1.0, 2.0)).to_logical::<f64>(1.0),
+            LogicalPosition::new(1.0, 2.0)
+        );
+
+        assert_eq!(
+            Position::new(PhysicalPosition::new(1, 2)).to_physical::<u32>(1.0),
+            PhysicalPosition::new(1, 2)
+        );
+        assert_eq!(
+            Position::new(PhysicalPosition::new(1, 2)).to_physical::<u32>(2.0),
+            PhysicalPosition::new(1, 2)
+        );
+        assert_eq!(
+            Position::new(LogicalPosition::new(1.0, 2.0)).to_physical::<u32>(1.0),
+            PhysicalPosition::new(1, 2)
+        );
+        assert_eq!(
+            Position::new(LogicalPosition::new(1.0, 2.0)).to_physical::<u32>(2.0),
+            PhysicalPosition::new(2, 4)
+        );
+    }
+
+    // Eat coverage for the Debug impls et al
+    #[test]
+    fn ensure_attrs_do_not_panic() {
+        let _ = format!("{:?}", LogicalPosition::<u32>::default().clone());
+        HashSet::new().insert(LogicalPosition::<u32>::default());
+
+        let _ = format!("{:?}", PhysicalPosition::<u32>::default().clone());
+        HashSet::new().insert(PhysicalPosition::<u32>::default());
+
+        let _ = format!("{:?}", LogicalSize::<u32>::default().clone());
+        HashSet::new().insert(LogicalSize::<u32>::default());
+
+        let _ = format!("{:?}", PhysicalSize::<u32>::default().clone());
+        HashSet::new().insert(PhysicalSize::<u32>::default());
+
+        let _ = format!("{:?}", Size::Physical((1, 2).into()).clone());
+        let _ = format!("{:?}", Position::Physical((1, 2).into()).clone());
+    }
+}