Add support for presser

Cargo.toml

@@ -22,6 +22,7 @@ include = [
 backtrace = "0.3"
 log = "0.4"
 thiserror = "1.0"
+presser = { version = "0.3" }
 # Only needed for vulkan.  Disable all default features as good practice,
 # such as the ability to link/load a Vulkan library.
 ash = { version = ">=0.34, <=0.37", optional = true, default-features = false, features = ["debug"] }

examples/vulkan-visualization/imgui_renderer.rs

@@ -309,7 +309,7 @@ impl ImGuiRenderer {
             let image_view = unsafe { device.create_image_view(&view_create_info, None) }?;
 
             // Create upload buffer
-            let (upload_buffer, upload_buffer_memory) = {
+            let (upload_buffer, mut upload_buffer_memory) = {
                 let create_info = vk::BufferCreateInfo::builder()
                     .size((font_atlas.width * font_atlas.height * 4) as u64)
                     .usage(vk::BufferUsageFlags::TRANSFER_SRC);
@@ -338,14 +338,10 @@ impl ImGuiRenderer {
             };
 
             // Copy font data to upload buffer
-            let dst = upload_buffer_memory.mapped_ptr().unwrap().cast().as_ptr();
-            unsafe {
-                std::ptr::copy_nonoverlapping(
-                    font_atlas.data.as_ptr(),
-                    dst,
-                    (font_atlas.width * font_atlas.height * 4) as usize,
-                );
-            }
+            let copy_record =
+                presser::copy_from_slice_to_offset(font_atlas.data, &mut upload_buffer_memory, 0)
+                    .unwrap();
+            assert_eq!(copy_record.copy_start_offset, 0);
 
             // Copy upload buffer to image
             record_and_submit_command_buffer(
@@ -633,13 +629,9 @@ impl ImGuiRenderer {
                 ],
             };
 
-            unsafe {
-                std::ptr::copy_nonoverlapping(
-                    &cbuffer_data,
-                    self.cb_allocation.mapped_ptr().unwrap().cast().as_ptr(),
-                    1,
-                )
-            };
+            let copy_record =
+                presser::copy_to_offset(&cbuffer_data, &mut self.cb_allocation, 0).unwrap();
+            assert_eq!(copy_record.copy_start_offset, 0);
         }
 
         let render_pass_begin_info = vk::RenderPassBeginInfo::builder()
@@ -716,49 +708,41 @@ impl ImGuiRenderer {
         let mut ib_offset = 0;
 
         for draw_list in imgui_draw_data.draw_lists() {
-            unsafe {
-                device.cmd_bind_vertex_buffers(
-                    cmd,
-                    0,
-                    &[self.vertex_buffer],
-                    &[vb_offset as u64 * std::mem::size_of::<imgui::DrawVert>() as u64],
-                )
-            };
-            unsafe {
-                device.cmd_bind_index_buffer(
-                    cmd,
-                    self.index_buffer,
-                    ib_offset as u64 * std::mem::size_of::<imgui::DrawIdx>() as u64,
-                    vk::IndexType::UINT16,
-                )
-            };
-
             {
                 let vertices = draw_list.vtx_buffer();
-                let dst_ptr = self
-                    .vb_allocation
-                    .mapped_ptr()
-                    .unwrap()
-                    .cast::<imgui::DrawVert>()
-                    .as_ptr();
-                let dst_ptr = unsafe { dst_ptr.offset(vb_offset) };
+                let copy_record = presser::copy_from_slice_to_offset(
+                    vertices,
+                    &mut self.vb_allocation,
+                    vb_offset,
+                )
+                .unwrap();
+                vb_offset = copy_record.copy_end_offset_padded;
+
                 unsafe {
-                    std::ptr::copy_nonoverlapping(vertices.as_ptr(), dst_ptr, vertices.len())
+                    device.cmd_bind_vertex_buffers(
+                        cmd,
+                        0,
+                        &[self.vertex_buffer],
+                        &[copy_record.copy_start_offset as _],
+                    )
                 };
-                vb_offset += vertices.len() as isize;
             }
 
             {
                 let indices = draw_list.idx_buffer();
-                let dst_ptr = self
-                    .ib_allocation
-                    .mapped_ptr()
-                    .unwrap()
-                    .cast::<imgui::DrawIdx>()
-                    .as_ptr();
-                let dst_ptr = unsafe { dst_ptr.offset(ib_offset) };
-                unsafe { std::ptr::copy_nonoverlapping(indices.as_ptr(), dst_ptr, indices.len()) };
-                ib_offset += indices.len() as isize;
+                let copy_record =
+                    presser::copy_from_slice_to_offset(indices, &mut self.ib_allocation, ib_offset)
+                        .unwrap();
+                ib_offset = copy_record.copy_end_offset_padded;
+
+                unsafe {
+                    device.cmd_bind_index_buffer(
+                        cmd,
+                        self.index_buffer,
+                        copy_record.copy_start_offset as _,
+                        vk::IndexType::UINT16,
+                    )
+                };
             }
 
             for command in draw_list.commands() {

src/vulkan/mod.rs

@@ -35,6 +35,90 @@ pub struct AllocatorCreateDesc {
     pub buffer_device_address: bool,
 }
 
+/// A piece of allocated memory.
+///
+/// Could be contained in its own individual underlying memory object or as a sub-region
+/// of a larger allocation.
+///
+/// # Copying data into a CPU-mapped [`Allocation`]
+///
+/// You'll very likely want to copy data into CPU-mapped [`Allocation`]s in order to send that data to the GPU.
+/// Doing this data transfer correctly without invoking undefined behavior can be quite fraught and non-obvious<sup>[\[1\]]</sup>.
+///
+/// To help you do this correctly, [`Allocation`] implements [`presser::Slab`], which means you can directly
+/// pass it in to many of `presser`'s [helper functions] (for example, [`copy_from_slice_to_offset`]).
+///
+/// In most cases, this will work perfectly. However, note that if you try to use an [`Allocation`] as a
+/// [`Slab`] and it is not valid to do so (if it is not CPU-mapped or if its `size > isize::MAX`),
+/// you will cause a panic. If you aren't sure about these conditions, you may use [`Allocation::try_as_mapped_slab`].
+///
+/// ## Example
+///
+/// Say we've created an [`Allocation`] called `my_allocation`, which is CPU-mapped.
+/// ```ignore
+/// let mut my_allocation: Allocation = my_allocator.allocate(...)?;
+/// ```
+///
+/// And we want to fill it with some data in the form of a `my_gpu_data: Vec<MyGpuVector>`, defined as such:
+///
+/// ```ignore
+/// // note that this is size(12) but align(16), thus we have 4 padding bytes.
+/// // this would mean a `&[MyGpuVector]` is invalid to cast as a `&[u8]`, but
+/// // we can still use `presser` to copy it directly in a valid manner.
+/// #[repr(C, align(16))]
+/// #[derive(Clone, Copy)]
+/// struct MyGpuVertex {
+///     x: f32,
+///     y: f32,
+///     z: f32,
+/// }
+///
+/// let my_gpu_data: Vec<MyGpuData> = make_vertex_data();
+/// ```
+///
+/// Depending on how the data we're copying will be used, the vulkan device may have a minimum
+/// alignment requirement for that data:
+///
+/// ```ignore
+/// let min_gpu_align = my_vulkan_device_specifications.min_alignment_thing;
+/// ```
+///
+/// Finally, we can use [`presser::copy_from_slice_to_offset_with_align`] to perform the copy,
+/// simply passing `&mut my_allocation` since [`Allocation`] implements [`Slab`].
+///
+/// ```ignore
+/// let copy_record = presser::copy_from_slice_to_offset_with_align(
+///     &my_gpu_data[..], // a slice containing all elements of my_gpu_data
+///     &mut my_allocation, // our Allocation
+///     0, // start as close to the beginning of the allocation as possible
+///     min_gpu_align, // the minimum alignment we queried previously
+/// )?;
+/// ```
+///
+/// It's important to note that the data may not have actually been copied starting at the requested
+/// `start_offset` (0 in the example above) depending on the alignment of the underlying allocation
+/// as well as the alignment requirements of `MyGpuVector` and the `min_gpu_align` we passed in. Thus,
+/// we can query the `copy_record` for the actual starting offset:
+///
+/// ```ignore
+/// let actual_data_start_offset = copy_record.copy_start_offset;
+/// ```
+///
+/// ## Safety
+///
+/// It is technically not fully safe to use an [`Allocation`] as a [`presser::Slab`] because we can't validate that the
+/// GPU is not using the data in the buffer while `self` is borrowed. However, trying
+/// to validate this statically is really hard and the community has basically decided that
+/// requiring `unsafe` for functions like this creates too much "unsafe-noise", ultimately making it
+/// harder to debug more insidious unsafety that is unrelated to GPU-CPU sync issues.
+///
+/// So, as would always be the case, you must ensure the GPU
+/// is not using the data in `self` for the duration that you hold the returned [`MappedAllocationSlab`].
+///
+/// [`Slab`]: presser::Slab
+/// [`copy_from_slice_to_offset`]: presser::copy_from_slice_to_offset
+/// [helper functions]: presser#functions
+/// [\[1\]]: presser#motivation
 #[derive(Debug)]
 pub struct Allocation {
     chunk_id: Option<std::num::NonZeroU64>,
@@ -57,6 +141,39 @@ unsafe impl Send for Allocation {}
 unsafe impl Sync for Allocation {}
 
 impl Allocation {
+    /// Tries to borrow the CPU-mapped memory that backs this allocation as a [`presser::Slab`], which you can then
+    /// use to safely copy data into the raw, potentially-uninitialized buffer.
+    /// See [the documentation of Allocation][Allocation#example] for an example of this.
+    ///
+    /// Returns [`None`] if `self.mapped_ptr()` is `None`, or if `self.size()` is greater than `isize::MAX` because
+    /// this could lead to undefined behavior.
+    ///
+    /// Note that [`Allocation`] implements [`Slab`] natively, so you can actually pass this allocation as a [`Slab`]
+    /// directly. However, if `self` is not actually a valid [`Slab`] (this function would return `None` as described above),
+    /// then trying to use it as a [`Slab`] will panic.
+    ///
+    /// # Safety
+    ///
+    /// See the note about safety in [the documentation of Allocation][Allocation#safety]
+    ///
+    /// [`Slab`]: presser::Slab
+    pub fn try_as_mapped_slab(&mut self) -> Option<MappedAllocationSlab<'_>> {
+        let mapped_ptr = self.mapped_ptr()?.cast().as_ptr();
+
+        if self.size > isize::MAX as _ {
+            return None;
+        }
+
+        // this will always succeed since size is <= isize::MAX which is < usize::MAX
+        let size = self.size as usize;
+
+        Some(MappedAllocationSlab {
+            _borrowed_alloc: self,
+            mapped_ptr,
+            size,
+        })
+    }
+
     pub fn chunk_id(&self) -> Option<std::num::NonZeroU64> {
         self.chunk_id
     }
@@ -126,6 +243,55 @@ impl Default for Allocation {
     }
 }
 
+/// A wrapper struct over a borrowed [`Allocation`] that infallibly implements [`presser::Slab`].
+///
+/// This type should be acquired by calling [`Allocation::try_as_mapped_slab`].
+pub struct MappedAllocationSlab<'a> {
+    _borrowed_alloc: &'a mut Allocation,
+    mapped_ptr: *mut u8,
+    size: usize,
+}
+
+// SAFETY: See the safety comment of Allocation::as_mapped_slab above.
+unsafe impl<'a> presser::Slab for MappedAllocationSlab<'a> {
+    fn base_ptr(&self) -> *const u8 {
+        self.mapped_ptr
+    }
+
+    fn base_ptr_mut(&mut self) -> *mut u8 {
+        self.mapped_ptr
+    }
+
+    fn size(&self) -> usize {
+        self.size
+    }
+}
+
+// SAFETY: See the safety comment of Allocation::as_mapped_slab above.
+unsafe impl presser::Slab for Allocation {
+    fn base_ptr(&self) -> *const u8 {
+        self.mapped_ptr
+            .expect("tried to use a non-mapped Allocation as a Slab")
+            .as_ptr()
+            .cast()
+    }
+
+    fn base_ptr_mut(&mut self) -> *mut u8 {
+        self.mapped_ptr
+            .expect("tried to use a non-mapped Allocation as a Slab")
+            .as_ptr()
+            .cast()
+    }
+
+    fn size(&self) -> usize {
+        if self.size > isize::MAX as _ {
+            panic!("tried to use an Allocation with size > isize::MAX as a Slab")
+        }
+        // this will always work if the above passed
+        self.size as usize
+    }
+}
+
 #[derive(Debug)]
 pub(crate) struct MemoryBlock {
     pub(crate) device_memory: vk::DeviceMemory,