Implement bytemuck behind a feature (#775)

emath/src/pos2.rs

@@ -8,8 +8,10 @@ use crate::*;
 ///
 /// Mathematically this is known as a "point", but the term position was chosen so not to
 /// conflict with the unit (one point = X physical pixels).
+#[repr(C)]
 #[derive(Clone, Copy, Default, PartialEq)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+#[cfg_attr(feature = "bytemuck", derive(bytemuck::Pod, bytemuck::Zeroable))]
 pub struct Pos2 {
     pub x: f32,
     pub y: f32,

emath/src/rect.rs

@@ -6,8 +6,10 @@ use crate::*;
 /// A rectangular region of space.
 ///
 /// Normally given in points, e.g. logical pixels.
+#[repr(C)]
 #[derive(Clone, Copy, Eq, PartialEq)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+#[cfg_attr(feature = "bytemuck", derive(bytemuck::Pod, bytemuck::Zeroable))]
 pub struct Rect {
     pub min: Pos2,
     pub max: Pos2,

emath/src/rect_transform.rs

@@ -3,7 +3,10 @@ use crate::*;
 /// Linearly transforms positions from one [`Rect`] to another.
 ///
 /// `RectTransform` stores the rectangles, and therefore supports clamping and culling.
+#[repr(C)]
 #[derive(Clone, Copy, Debug, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+#[cfg_attr(feature = "bytemuck", derive(bytemuck::Pod, bytemuck::Zeroable))]
 pub struct RectTransform {
     from: Rect,
     to: Rect,

emath/src/rot2.rs

@@ -13,7 +13,10 @@ use super::Vec2;
 //
 /// Normally a `Rot2` is normalized (unit-length).
 /// If not, it will also scale vectors.
+#[repr(C)]
 #[derive(Clone, Copy, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+#[cfg_attr(feature = "bytemuck", derive(bytemuck::Pod, bytemuck::Zeroable))]
 pub struct Rot2 {
     /// angle.sin()
     s: f32,

emath/src/vec2.rs

@@ -6,8 +6,10 @@ use std::ops::{Add, AddAssign, Div, Mul, MulAssign, Neg, Sub, SubAssign};
 /// emath represents positions using [`crate::Pos2`].
 ///
 /// Normally the units are points (logical pixels).
+#[repr(C)]
 #[derive(Clone, Copy, Default, PartialEq)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+#[cfg_attr(feature = "bytemuck", derive(bytemuck::Pod, bytemuck::Zeroable))]
 pub struct Vec2 {
     pub x: f32,
     pub y: f32,