Use bytemuck for slice cast (#36)

Use the `bytemuck` package for slice casting to byte, instead of rolling
some manual unsafe one.

Fixes #29

bin/weldr/Cargo.toml

@@ -35,4 +35,5 @@ serde_json = "1.0"
 serde_repr = "0.1"
 ordered-float = "2.0"
 log = "0.4"
-atty = "0.2"
+atty = "0.2"
+bytemuck = { version = "1", features = ["derive"] }

bin/weldr/src/convert.rs

@@ -1,7 +1,6 @@
 //! Action to convert an LDraw file to another format.
 
 use crate::{
-    as_u8_slice,
     error::{Error, Utf8Error},
     gltf, Action, App, DiskResolver, GeometryCache,
 };
@@ -252,8 +251,9 @@ impl ConvertCommand {
         gltf: &mut gltf::Gltf,
         buffer: &mut Vec<u8>,
     ) {
+        // TODO: glTF is LE only; should convert on BE platforms
         let vertices = &geometry_cache.vertices;
-        let vertices_bytes: &[u8] = unsafe { as_u8_slice(vertices) };
+        let vertices_bytes: &[u8] = bytemuck::cast_slice(&vertices[..]);
 
         // TODO: Line indices?
         let vertex_buffer_view_index = gltf.buffer_views.len() as u32;
@@ -293,16 +293,19 @@ impl ConvertCommand {
             let attributes = HashMap::from([("POSITION".to_string(), gltf.accessors.len() as u32)]);
             gltf.accessors.push(vertex_accessor);
 
-            // TODO: Use bytemuck instead.
-            let triangle_indices = &geometry_cache.triangle_indices;
-            let triangle_indices_bytes: &[u8] = unsafe { as_u8_slice(triangle_indices) };
+            // TODO: glTF is LE only; should convert on BE platforms
+            let triangle_indices_bytes: &[u8] =
+                bytemuck::cast_slice(&geometry_cache.triangle_indices[..]);
 
+            let byte_offset = buffer.len() as u32;
+            let byte_length = triangle_indices_bytes.len() as u32;
             let index_buffer_view_index = gltf.buffer_views.len() as u32;
+
             gltf.buffer_views.push(gltf::BufferView {
                 name: Some("index_buffer".to_string()),
                 buffer_index: 0,
-                byte_length: triangle_indices_bytes.len() as u32,
-                byte_offset: buffer.len() as u32,
+                byte_length,
+                byte_offset,
                 byte_stride: None,
                 target: Some(gltf::BufferTarget::ElementArrayBuffer as u32),
             });

bin/weldr/src/weldr.rs

@@ -337,14 +337,6 @@ impl GeometryCache {
     }
 }
 
-/// Transform a slice of something sized into a slice of u8, for binary writing.
-unsafe fn as_u8_slice<T: Sized>(p: &[T]) -> &[u8] {
-    ::std::slice::from_raw_parts(
-        p.as_ptr() as *const u8,
-        ::std::mem::size_of::<T>() * p.len(),
-    )
-}
-
 #[cfg(not(target_os = "windows"))]
 fn is_tty() -> bool {
     atty::is(atty::Stream::Stderr)
@@ -400,7 +392,7 @@ mod tests {
     fn test_as_u8_slice() {
         assert_eq!(12, std::mem::size_of::<Vec3>());
         let v = vec![Vec3::new(1.0, 2.0, 4.0), Vec3::new(1.0, 2.0, 4.0)];
-        let b: &[u8] = unsafe { as_u8_slice(&v[..]) };
+        let b: &[u8] = bytemuck::cast_slice(&v[..]);
         assert_eq!(24, b.len());
     }
 

lib/Cargo.toml

@@ -28,6 +28,6 @@ path = "src/lib.rs"
 
 [dependencies]
 nom = "7.1.3"
-glam = "0.23.0"
+glam = { version = "0.23.0", features = ["bytemuck"] }
 log = "0.4"
 base64 = "0.21.0"