Implement bytemuck behind a feature (#775)

epaint/Cargo.toml

@@ -34,6 +34,7 @@ cint = { version = "^0.2.2", optional = true }
 nohash-hasher = "0.2"
 parking_lot = { version = "0.11", optional = true } # Using parking_lot over std::sync::Mutex gives 50% speedups in some real-world scenarios.
 serde = { version = "1", features = ["derive"], optional = true }
+bytemuck = { version = "1.7.2", features = ["derive"], optional = true }
 
 [features]
 default = ["default_fonts", "multi_threaded"]
@@ -53,6 +54,9 @@ mint = ["emath/mint"]
 # implement serde on most types.
 serialize = ["serde", "emath/serde"]
 
+# implement bytemuck on most types.
+convert_bytemuck = ["bytemuck", "emath/bytemuck"]
+
 single_threaded = ["atomic_refcell"]
 
 # Only needed if you plan to use the same fonts from multiple threads.

epaint/src/color.rs

@@ -13,8 +13,10 @@
 ///
 /// Internally this uses 0-255 gamma space `sRGBA` color with premultiplied alpha.
 /// Alpha channel is in linear space.
+#[repr(C)]
 #[derive(Clone, Copy, Debug, Default, Eq, Hash, PartialEq)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+#[cfg_attr(feature = "bytemuck", derive(bytemuck::Pod, bytemuck::Zeroable))]
 pub struct Color32(pub(crate) [u8; 4]);
 
 impl std::ops::Index<usize> for Color32 {

epaint/src/mesh.rs

@@ -7,6 +7,7 @@ use emath::*;
 #[repr(C)]
 #[derive(Clone, Copy, Debug, Default, PartialEq)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+#[cfg_attr(feature = "bytemuck", derive(bytemuck::Pod, bytemuck::Zeroable))]
 pub struct Vertex {
     /// Logical pixel coordinates (points).
     /// (0,0) is the top left corner of the screen.