feat(lambda-rs): Add write_slice and write_bytes to Buffer

crates/lambda-rs/examples/indexed_multi_vertex_buffers.rs

@@ -89,12 +89,16 @@ struct PositionVertex {
   position: [f32; 3],
 }
 
+unsafe impl lambda::pod::PlainOldData for PositionVertex {}
+
 #[repr(C)]
 #[derive(Clone, Copy, Debug)]
 struct ColorVertex {
   color: [f32; 3],
 }
 
+unsafe impl lambda::pod::PlainOldData for ColorVertex {}
+
 // --------------------------------- COMPONENT ---------------------------------
 
 pub struct IndexedMultiBufferExample {

crates/lambda-rs/examples/instanced_quads.rs

@@ -92,13 +92,17 @@ struct QuadVertex {
   position: [f32; 3],
 }
 
+unsafe impl lambda::pod::PlainOldData for QuadVertex {}
+
 #[repr(C)]
 #[derive(Clone, Copy, Debug)]
 struct InstanceData {
   offset: [f32; 3],
   color: [f32; 3],
 }
 
+unsafe impl lambda::pod::PlainOldData for InstanceData {}
+
 // --------------------------------- COMPONENT ---------------------------------
 
 /// Component that renders a grid of instanced quads.

crates/lambda-rs/examples/uniform_buffer_triangle.rs

@@ -101,6 +101,8 @@ pub struct GlobalsUniform {
   pub render_matrix: [[f32; 4]; 4],
 }
 
+unsafe impl lambda::pod::PlainOldData for GlobalsUniform {}
+
 // --------------------------------- COMPONENT ---------------------------------
 
 pub struct UniformBufferExample {

crates/lambda-rs/src/lib.rs

@@ -14,6 +14,7 @@
 pub mod component;
 pub mod events;
 pub mod math;
+pub mod pod;
 pub mod render;
 pub mod runtime;
 pub mod runtimes;

crates/lambda-rs/src/pod.rs

@@ -0,0 +1,42 @@
+//! Plain-old-data marker trait for safe byte uploads.
+//!
+//! The engine frequently uploads CPU data into GPU buffers by reinterpreting
+//! a value or slice as raw bytes. This is only sound for types that are safe
+//! to view as bytes.
+
+/// Marker trait for types that are safe to reinterpret as raw bytes.
+///
+/// This trait is required by typed buffer upload APIs (for example
+/// `render::buffer::Buffer::write_value` and `render::buffer::Buffer::write_slice`)
+/// and typed buffer creation APIs (for example
+/// `render::buffer::BufferBuilder::build`) because those operations upload the
+/// in-memory representation of a value to the GPU.
+///
+/// # Safety
+/// Types implementing `PlainOldData` MUST satisfy all of the following:
+/// - Every byte of the value is initialized (including any padding bytes).
+/// - The type has no pointers or references that would be invalidated by a
+///   raw byte copy.
+/// - The type's byte representation is stable for GPU consumption. Prefer
+///   `#[repr(C)]` or `#[repr(transparent)]`.
+///
+/// Implementing this trait incorrectly can cause undefined behavior.
+pub unsafe trait PlainOldData: Copy {}
+
+unsafe impl PlainOldData for u8 {}
+unsafe impl PlainOldData for i8 {}
+unsafe impl PlainOldData for u16 {}
+unsafe impl PlainOldData for i16 {}
+unsafe impl PlainOldData for u32 {}
+unsafe impl PlainOldData for i32 {}
+unsafe impl PlainOldData for u64 {}
+unsafe impl PlainOldData for i64 {}
+unsafe impl PlainOldData for u128 {}
+unsafe impl PlainOldData for i128 {}
+unsafe impl PlainOldData for usize {}
+unsafe impl PlainOldData for isize {}
+unsafe impl PlainOldData for f32 {}
+unsafe impl PlainOldData for f64 {}
+unsafe impl PlainOldData for bool {}
+unsafe impl PlainOldData for char {}
+unsafe impl<T: PlainOldData, const N: usize> PlainOldData for [T; N] {}

crates/lambda-rs/src/render/buffer.rs

@@ -27,6 +27,7 @@ use super::{
   mesh::Mesh,
   RenderContext,
 };
+pub use crate::pod::PlainOldData;
 
 /// High‑level classification for buffers created by the engine.
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
@@ -140,17 +141,80 @@ impl Buffer {
 
   /// Write a single plain-old-data value into this buffer at the specified
   /// byte offset. This is intended for updating uniform buffer contents from
-  /// the CPU. The `data` type must be trivially copyable.
-  pub fn write_value<T: Copy>(&self, gpu: &Gpu, offset: u64, data: &T) {
-    let bytes = unsafe {
-      std::slice::from_raw_parts(
-        (data as *const T) as *const u8,
-        std::mem::size_of::<T>(),
-      )
-    };
+  /// the CPU. The `data` type must implement `PlainOldData`.
+  pub fn write_value<T: PlainOldData>(&self, gpu: &Gpu, offset: u64, data: &T) {
+    let bytes = value_as_bytes(data);
+    self.write_bytes(gpu, offset, bytes);
+  }
 
-    self.buffer.write_bytes(gpu.platform(), offset, bytes);
+  /// Write raw bytes into this buffer at the specified byte offset.
+  ///
+  /// This is useful when data is already available as a byte slice (for
+  /// example, asset blobs or staging buffers).
+  ///
+  /// Example
+  /// ```rust,ignore
+  /// let raw_data: &[u8] = load_binary_data();
+  /// buffer.write_bytes(render_context.gpu(), 0, raw_data);
+  /// ```
+  pub fn write_bytes(&self, gpu: &Gpu, offset: u64, data: &[u8]) {
+    self.buffer.write_bytes(gpu.platform(), offset, data);
   }
+
+  /// Write a slice of plain-old-data values into this buffer at the
+  /// specified byte offset.
+  ///
+  /// This is intended for uploading arrays of vertices, indices, instance
+  /// data, or uniform blocks. The `T` type MUST be plain-old-data (POD) and
+  /// safely representable as bytes. This is enforced by requiring `T` to
+  /// implement `PlainOldData`.
+  ///
+  /// Example
+  /// ```rust,ignore
+  /// let transforms: Vec<InstanceTransform> = compute_transforms();
+  /// instance_buffer
+  ///   .write_slice(render_context.gpu(), 0, &transforms)
+  ///   .unwrap();
+  /// ```
+  pub fn write_slice<T: PlainOldData>(
+    &self,
+    gpu: &Gpu,
+    offset: u64,
+    data: &[T],
+  ) -> Result<(), &'static str> {
+    let bytes = slice_as_bytes(data)?;
+    self.write_bytes(gpu, offset, bytes);
+    return Ok(());
+  }
+}
+
+fn value_as_bytes<T: PlainOldData>(data: &T) -> &[u8] {
+  let bytes = unsafe {
+    std::slice::from_raw_parts(
+      (data as *const T) as *const u8,
+      std::mem::size_of::<T>(),
+    )
+  };
+  return bytes;
+}
+
+fn checked_byte_len(
+  element_size: usize,
+  element_count: usize,
+) -> Result<usize, &'static str> {
+  let Some(byte_len) = element_size.checked_mul(element_count) else {
+    return Err("Buffer byte length overflow.");
+  };
+  return Ok(byte_len);
+}
+
+fn slice_as_bytes<T: PlainOldData>(data: &[T]) -> Result<&[u8], &'static str> {
+  let element_size = std::mem::size_of::<T>();
+  let byte_len = checked_byte_len(element_size, data.len())?;
+
+  let bytes =
+    unsafe { std::slice::from_raw_parts(data.as_ptr() as *const u8, byte_len) };
+  return Ok(bytes);
 }
 
 /// Strongly‑typed uniform buffer wrapper for ergonomics and safety.
@@ -176,7 +240,7 @@ pub struct UniformBuffer<T> {
   _phantom: core::marker::PhantomData<T>,
 }
 
-impl<T: Copy> UniformBuffer<T> {
+impl<T: PlainOldData> UniformBuffer<T> {
   /// Create a new uniform buffer initialized with `initial`.
   pub fn new(
     gpu: &Gpu,
@@ -287,22 +351,23 @@ impl BufferBuilder {
   /// Create a buffer initialized with the provided `data`.
   ///
   /// Returns an error if the resolved length would be zero.
-  pub fn build<Data: Copy>(
+  ///
+  /// The element type MUST implement `PlainOldData` because the engine uploads
+  /// the in-memory representation to the GPU.
+  pub fn build<Data: PlainOldData>(
     &self,
     gpu: &Gpu,
     data: Vec<Data>,
   ) -> Result<Buffer, &'static str> {
     let element_size = std::mem::size_of::<Data>();
     let buffer_length = self.resolve_length(element_size, data.len())?;
+    let byte_len = checked_byte_len(element_size, data.len())?;
 
     // SAFETY: Converting data to bytes is safe because its underlying
-    // type, Data, is constrained to Copy and the lifetime of the slice does
-    // not outlive data.
+    // type, Data, is constrained to PlainOldData and the lifetime of the slice
+    // does not outlive data.
     let bytes = unsafe {
-      std::slice::from_raw_parts(
-        data.as_ptr() as *const u8,
-        element_size * data.len(),
-      )
+      std::slice::from_raw_parts(data.as_ptr() as *const u8, byte_len)
     };
 
     let mut builder = platform_buffer::BufferBuilder::new()
@@ -346,7 +411,7 @@ impl BufferBuilder {
     data_len: usize,
   ) -> Result<usize, &'static str> {
     let buffer_length = if self.buffer_length == 0 {
-      element_size * data_len
+      checked_byte_len(element_size, data_len)?
     } else {
       self.buffer_length
     };
@@ -375,4 +440,40 @@ mod tests {
     // Test module is a child of this module and can access private fields.
     assert_eq!(builder.label.as_deref(), Some("buffer-test"));
   }
+
+  #[test]
+  fn resolve_length_rejects_overflow() {
+    let builder = BufferBuilder::new();
+    let result = builder.resolve_length(usize::MAX, 2);
+    assert!(result.is_err());
+  }
+
+  #[test]
+  fn value_as_bytes_matches_native_bytes() {
+    let value: u32 = 0x1122_3344;
+    let expected = value.to_ne_bytes();
+    assert_eq!(value_as_bytes(&value), expected.as_slice());
+  }
+
+  #[test]
+  fn slice_as_bytes_matches_native_bytes() {
+    let values: [u16; 3] = [0x1122, 0x3344, 0x5566];
+    let mut expected: Vec<u8> = Vec::new();
+    for value in values {
+      expected.extend_from_slice(&value.to_ne_bytes());
+    }
+    assert_eq!(slice_as_bytes(&values).unwrap(), expected.as_slice());
+  }
+
+  #[test]
+  fn slice_as_bytes_empty_is_empty() {
+    let values: [u32; 0] = [];
+    assert_eq!(slice_as_bytes(&values).unwrap(), &[]);
+  }
+
+  #[test]
+  fn checked_byte_len_rejects_overflow() {
+    let result = checked_byte_len(usize::MAX, 2);
+    assert!(result.is_err());
+  }
 }

crates/lambda-rs/src/render/vertex.rs

@@ -78,6 +78,8 @@ pub struct Vertex {
   pub color: [f32; 3],
 }
 
+unsafe impl crate::pod::PlainOldData for Vertex {}
+
 /// Builder for constructing a `Vertex` instance incrementally.
 #[derive(Clone, Copy, Debug)]
 pub struct VertexBuilder {

docs/tutorials/indexed-draws-and-multiple-vertex-buffers.md

@@ -3,13 +3,13 @@ title: "Indexed Draws and Multiple Vertex Buffers"
 document_id: "indexed-draws-multiple-vertex-buffers-tutorial-2025-11-22"
 status: "draft"
 created: "2025-11-22T00:00:00Z"
-last_updated: "2026-01-16T00:00:00Z"
-version: "0.3.1"
+last_updated: "2026-01-24T00:00:00Z"
+version: "0.3.3"
 engine_workspace_version: "2023.1.30"
 wgpu_version: "26.0.1"
 shader_backend_default: "naga"
 winit_version: "0.29.10"
-repo_commit: "9435ad1491b5930054117406abe08dd1c37f2102"
+repo_commit: "df476b77e1f2a17818869c3218cf223ab935c456"
 owners: ["lambda-sh"]
 reviewers: ["engine", "rendering"]
 tags: ["tutorial", "graphics", "indexed-draws", "vertex-buffers", "rust", "wgpu"]
@@ -123,14 +123,18 @@ struct PositionVertex {
   position: [f32; 3],
 }
 
+unsafe impl lambda::pod::PlainOldData for PositionVertex {}
+
 #[repr(C)]
 #[derive(Clone, Copy, Debug)]
 struct ColorVertex {
   color: [f32; 3],
 }
+
+unsafe impl lambda::pod::PlainOldData for ColorVertex {}
 ```
 
-The shader `location` qualifiers match the vertex buffer layouts declared on the pipeline, and the `PositionVertex` and `ColorVertex` types mirror the `vec3` inputs as `[f32; 3]` arrays in Rust.
+The shader `location` qualifiers match the vertex buffer layouts declared on the pipeline, and the `PositionVertex` and `ColorVertex` types mirror the `vec3` inputs as `[f32; 3]` arrays in Rust. The `PlainOldData` implementations mark the types as safe for `BufferBuilder` uploads.
 
 ### Step 2 — Component State and Shader Construction <a name="step-2"></a>
 
@@ -498,6 +502,8 @@ This tutorial demonstrates how indexed draws and multiple vertex buffers combine
 
 ## Changelog <a name="changelog"></a>
 
+- 2026-01-24 (v0.3.3) — Move `PlainOldData` to `lambda::pod::PlainOldData`.
+- 2026-01-24 (v0.3.2) — Add `PlainOldData` requirements for typed buffer data.
 - 2026-01-16 (v0.3.1) — Update resize handling examples to use `event_mask()` and `on_window_event`.
 - 2025-12-15 (v0.3.0) — Update builder API calls to use `render_context.gpu()` and add `surface_format`/`depth_format` parameters to `RenderPassBuilder` and `RenderPipelineBuilder`.
 - 2025-11-23 (v0.2.0) — Filled in the implementation steps for the indexed draws and multiple vertex buffers tutorial and aligned the narrative with the `indexed_multi_vertex_buffers` example.

docs/tutorials/instanced-quads.md

@@ -3,13 +3,13 @@ title: "Instanced Rendering: Grid of Colored Quads"
 document_id: "instanced-quads-tutorial-2025-11-25"
 status: "draft"
 created: "2025-11-25T00:00:00Z"
-last_updated: "2026-01-16T00:00:00Z"
-version: "0.2.1"
+last_updated: "2026-01-24T00:00:00Z"
+version: "0.2.3"
 engine_workspace_version: "2023.1.30"
 wgpu_version: "26.0.1"
 shader_backend_default: "naga"
 winit_version: "0.29.10"
-repo_commit: "9435ad1491b5930054117406abe08dd1c37f2102"
+repo_commit: "df476b77e1f2a17818869c3218cf223ab935c456"
 owners: ["lambda-sh"]
 reviewers: ["engine", "rendering"]
 tags: ["tutorial", "graphics", "instancing", "vertex-buffers", "rust", "wgpu"]
@@ -156,13 +156,17 @@ struct QuadVertex {
   position: [f32; 3],
 }
 
+unsafe impl lambda::pod::PlainOldData for QuadVertex {}
+
 #[repr(C)]
 #[derive(Clone, Copy, Debug)]
 struct InstanceData {
   offset: [f32; 3],
   color: [f32; 3],
 }
 
+unsafe impl lambda::pod::PlainOldData for InstanceData {}
+
 pub struct InstancedQuadsExample {
   vertex_shader: Shader,
   fragment_shader: Shader,
@@ -210,7 +214,7 @@ impl Default for InstancedQuadsExample {
 }
 ```
 
-The `QuadVertex` and `InstanceData` structures mirror the GLSL inputs as arrays of `f32`, and the component tracks resource identifiers and counts that are populated during attachment. The `Default` implementation constructs shader objects from the GLSL source so that the component is ready to build a pipeline when it receives a `RenderContext`.
+The `QuadVertex` and `InstanceData` structures mirror the GLSL inputs as arrays of `f32`, and the component tracks resource identifiers and counts that are populated during attachment. The `PlainOldData` implementations mark the types as safe for `BufferBuilder` uploads, which reinterpret values as raw bytes when initializing GPU buffers. The `Default` implementation constructs shader objects from the GLSL source so that the component is ready to build a pipeline when it receives a `RenderContext`.
 
 ### Step 3 — Render Pass, Geometry, Instances, and Buffers <a name="step-3"></a>
 
@@ -510,6 +514,8 @@ This tutorial demonstrates how the `lambda-rs` crate uses per-vertex and per-ins
 
 ## Changelog <a name="changelog"></a>
 
+- 2026-01-24 (v0.2.3) — Move `PlainOldData` to `lambda::pod::PlainOldData`.
+- 2026-01-24 (v0.2.2) — Add `PlainOldData` requirements for typed buffer data.
 - 2026-01-16 (v0.2.1) — Update resize handling examples to use `event_mask()` and `on_window_event`.
 - 2025-12-15 (v0.2.0) — Update builder API calls to use `render_context.gpu()` and add `surface_format`/`depth_format` parameters to `RenderPassBuilder` and `RenderPipelineBuilder`.
 - 2025-11-25 (v0.1.1) — Align feature naming with `render-validation-instancing` and update metadata.