Document that various sizes and offsets are in bytes.

Document that the following are in bytes:
- `BindingType::Buffer::min_binding_size`
- `BufferBinding::offset`
- `BufferBinding::size`
- `BufferDescriptor::size`

Clarify other requirements as well.

Fixes gfx-rs#3768.

wgpu-types/src/lib.rs

@@ -4276,7 +4276,7 @@ impl_bitflags!(BufferUsages);
 pub struct BufferDescriptor<L> {
     /// Debug label of a buffer. This will show up in graphics debuggers for easy identification.
     pub label: L,
-    /// Size of a buffer.
+    /// Size of a buffer, in bytes.
     pub size: BufferAddress,
     /// Usages of a buffer. If the buffer is used in any way that isn't specified here, the operation
     /// will panic.
@@ -5531,18 +5531,41 @@ pub enum BindingType {
     Buffer {
         /// Sub-type of the buffer binding.
         ty: BufferBindingType,
+
         /// Indicates that the binding has a dynamic offset.
         ///
-        /// One offset must be passed to [`RenderPass::set_bind_group`][RPsbg] for each dynamic
-        /// binding in increasing order of binding number.
+        /// One offset must be passed to [`RenderPass::set_bind_group`][RPsbg]
+        /// for each dynamic binding in increasing order of binding number.
         ///
         /// [RPsbg]: ../wgpu/struct.RenderPass.html#method.set_bind_group
         #[cfg_attr(any(feature = "trace", feature = "replay"), serde(default))]
         has_dynamic_offset: bool,
-        /// Minimum size of the corresponding `BufferBinding` required to match this entry.
-        /// When pipeline is created, the size has to cover at least the corresponding structure in the shader
-        /// plus one element of the unbound array, which can only be last in the structure.
-        /// If `None`, the check is performed at draw call time instead of pipeline and bind group creation.
+
+        /// The minimum size for a [`BufferBinding`] matching this entry, in bytes.
+        ///
+        /// If this is `Some(size)`:
+        ///
+        /// - When calling [`create_bind_group`], the resource at this bind point
+        ///   must be a [`BindingResource::Buffer`] whose effective size is at
+        ///   least `size`.
+        ///
+        /// - When calling [`create_render_pipeline`] or [`create_compute_pipeline`],
+        ///   `size` must be at least the [minimum buffer binding size] for the
+        ///   shader module global at this bind point: large enough to hold the
+        ///   global's value, along with one element of a trailing runtime-sized
+        ///   array, if present.
+        ///
+        /// If this is `None`:
+        ///
+        /// - Each draw or dispatch command checks that the buffer range at this
+        ///   bind point satisfies the [minimum buffer binding size].
+        ///
+        /// [`BufferBinding`]: ../wgpu/struct.BufferBinding.html
+        /// [`create_bind_group`]: ../wgpu/struct.Device.html#method.create_bind_group
+        /// [`BindingResource::Buffer`]: ../wgpu/enum.BindingResource.html#variant.Buffer
+        /// [minimum buffer binding size]: https://www.w3.org/TR/webgpu/#minimum-buffer-binding-size
+        /// [`create_render_pipeline`]: ../wgpu/struct.Device.html#method.create_render_pipeline
+        /// [`create_compute_pipeline`]: ../wgpu/struct.Device.html#method.create_compute_pipeline
         #[cfg_attr(any(feature = "trace", feature = "replay"), serde(default))]
         min_binding_size: Option<BufferSize>,
     },

wgpu/src/lib.rs

@@ -772,13 +772,25 @@ static_assertions::assert_impl_all!(BindingResource: Send, Sync);
 pub struct BufferBinding<'a> {
     /// The buffer to bind.
     pub buffer: &'a Buffer,
-    /// Base offset of the buffer. For bindings with `dynamic == true`, this offset
-    /// will be added to the dynamic offset provided in [`RenderPass::set_bind_group`].
+
+    /// Base offset of the buffer, in bytes.
     ///
-    /// The offset has to be aligned to [`Limits::min_uniform_buffer_offset_alignment`]
-    /// or [`Limits::min_storage_buffer_offset_alignment`] appropriately.
+    /// If the [`has_dynamic_offset`] field of this buffer's layout entry is
+    /// `true`, the offset here will be added to the dynamic offset passed to
+    /// [`RenderPass::set_bind_group`] or [`ComputePass::set_bind_group`].
+    ///
+    /// If the buffer was created with [`BufferUsages::UNIFORM`], then this
+    /// offset must be a multiple of
+    /// [`Limits::min_uniform_buffer_offset_alignment`].
+    ///
+    /// If the buffer was created with [`BufferUsages::STORAGE`], then this
+    /// offset must be a multiple of
+    /// [`Limits::min_storage_buffer_offset_alignment`].
+    ///
+    /// [`has_dynamic_offset`]: BindingType::Buffer::has_dynamic_offset
     pub offset: BufferAddress,
-    /// Size of the binding, or `None` for using the rest of the buffer.
+
+    /// Size of the binding in bytes, or `None` for using the rest of the buffer.
     pub size: Option<BufferSize>,
 }
 static_assertions::assert_impl_all!(BufferBinding: Send, Sync);