[wgpu-core/-hal] move raytracing alignments into hal (#6563)

CHANGELOG.md

@@ -104,6 +104,7 @@ By @ErichDonGubler in [#6456](https://github.com/gfx-rs/wgpu/pull/6456), [#6148]
 #### General
 
 - Return submission index in `map_async` and `on_submitted_work_done` to track down completion of async callbacks. By @eliemichel in [#6360](https://github.com/gfx-rs/wgpu/pull/6360).
+- Move raytracing alignments into HAL instead of in core. By @Vecvec in [#6563](https://github.com/gfx-rs/wgpu/pull/6563).
 
 ### Changes
 

wgpu-core/src/command/ray_tracing.rs

@@ -5,7 +5,7 @@ use crate::{
     id::CommandEncoderId,
     init_tracker::MemoryInitKind,
     ray_tracing::{
-        tlas_instance_into_bytes, BlasAction, BlasBuildEntry, BlasGeometries, BlasTriangleGeometry,
+        BlasAction, BlasBuildEntry, BlasGeometries, BlasTriangleGeometry,
         BuildAccelerationStructureError, TlasAction, TlasBuildEntry, TlasInstance, TlasPackage,
         TraceBlasBuildEntry, TraceBlasGeometries, TraceBlasTriangleGeometry, TraceTlasInstance,
         TraceTlasPackage, ValidateBlasActionsError, ValidateTlasActionsError,
@@ -60,9 +60,6 @@ struct TlasBufferStore {
     entry: TlasBuildEntry,
 }
 
-// TODO: Get this from the device (e.g. VkPhysicalDeviceAccelerationStructurePropertiesKHR.minAccelerationStructureScratchOffsetAlignment) this is currently the largest possible some devices have 0, 64, 128 (lower limits) so this could create excess allocation (Note: dx12 has 256).
-const SCRATCH_BUFFER_ALIGNMENT: u32 = 256;
-
 impl Global {
     // Currently this function is very similar to its safe counterpart, however certain parts of it are very different,
     // making for the two to be implemented differently, the main difference is this function has separate buffers for each
@@ -193,6 +190,7 @@ impl Global {
             &mut scratch_buffer_blas_size,
             &mut blas_storage,
             hub,
+            device.alignments.ray_tracing_scratch_buffer_alignment,
         )?;
 
         let mut scratch_buffer_tlas_size = 0;
@@ -260,7 +258,7 @@ impl Global {
             let scratch_buffer_offset = scratch_buffer_tlas_size;
             scratch_buffer_tlas_size += align_to(
                 tlas.size_info.build_scratch_size as u32,
-                SCRATCH_BUFFER_ALIGNMENT,
+                device.alignments.ray_tracing_scratch_buffer_alignment,
             ) as u64;
 
             tlas_storage.push(UnsafeTlasStore {
@@ -508,6 +506,7 @@ impl Global {
             &mut scratch_buffer_blas_size,
             &mut blas_storage,
             hub,
+            device.alignments.ray_tracing_scratch_buffer_alignment,
         )?;
         let mut tlas_lock_store = Vec::<(Option<TlasPackage>, Arc<Tlas>)>::new();
 
@@ -535,7 +534,7 @@ impl Global {
             let scratch_buffer_offset = scratch_buffer_tlas_size;
             scratch_buffer_tlas_size += align_to(
                 tlas.size_info.build_scratch_size as u32,
-                SCRATCH_BUFFER_ALIGNMENT,
+                device.alignments.ray_tracing_scratch_buffer_alignment,
             ) as u64;
 
             let first_byte_index = instance_buffer_staging_source.len();
@@ -558,10 +557,13 @@ impl Global {
 
                 cmd_buf_data.trackers.blas_s.set_single(blas.clone());
 
-                instance_buffer_staging_source.extend(tlas_instance_into_bytes(
+                instance_buffer_staging_source.extend(device.raw().tlas_instance_to_bytes(
-                    &instance,
+                    hal::TlasInstance {
-                    blas.handle,
+                        transform: *instance.transform,
-                    device.backend(),
+                        custom_index: instance.custom_index,
+                        mask: instance.mask,
+                        blas_address: blas.handle,
+                    },
                 ));
 
                 instance_count += 1;
@@ -1013,6 +1015,7 @@ fn iter_buffers<'a, 'b>(
     scratch_buffer_blas_size: &mut u64,
     blas_storage: &mut Vec<BlasStore<'a>>,
     hub: &Hub,
+    ray_tracing_scratch_buffer_alignment: u32,
 ) -> Result<(), BuildAccelerationStructureError> {
     let mut triangle_entries =
         Vec::<hal::AccelerationStructureTriangles<dyn hal::DynBuffer>>::new();
@@ -1192,7 +1195,7 @@ fn iter_buffers<'a, 'b>(
             let scratch_buffer_offset = *scratch_buffer_blas_size;
             *scratch_buffer_blas_size += align_to(
                 blas.size_info.build_scratch_size as u32,
-                SCRATCH_BUFFER_ALIGNMENT,
+                ray_tracing_scratch_buffer_alignment,
             ) as u64;
 
             blas_storage.push(BlasStore {

wgpu-core/src/device/ray_tracing.rs

@@ -12,7 +12,7 @@ use crate::{
     global::Global,
     id::{self, BlasId, TlasId},
     lock::RwLock,
-    ray_tracing::{get_raw_tlas_instance_size, CreateBlasError, CreateTlasError},
+    ray_tracing::{CreateBlasError, CreateTlasError},
     resource, LabelHelpers,
 };
 use hal::AccelerationStructureTriangleIndices;
@@ -135,7 +135,7 @@ impl Device {
         .map_err(DeviceError::from_hal)?;
 
         let instance_buffer_size =
-            get_raw_tlas_instance_size(self.backend()) * desc.max_instances.max(1) as usize;
+            self.alignments.raw_tlas_instance_size * desc.max_instances.max(1) as usize;
         let instance_buffer = unsafe {
             self.raw().create_buffer(&hal::BufferDescriptor {
                 label: Some("(wgpu-core) instances_buffer"),

wgpu-core/src/ray_tracing.rs

@@ -13,8 +13,8 @@ use crate::{
     id::{BlasId, BufferId, TlasId},
     resource::CreateBufferError,
 };
-use std::{mem::size_of, sync::Arc};
+use std::num::NonZeroU64;
-use std::{num::NonZeroU64, slice};
+use std::sync::Arc;
 
 use crate::resource::{Blas, ResourceErrorIdent, Tlas};
 use thiserror::Error;
@@ -276,48 +276,3 @@ pub struct TraceTlasPackage {
     pub instances: Vec<Option<TraceTlasInstance>>,
     pub lowest_unmodified: u32,
 }
-
-pub(crate) fn get_raw_tlas_instance_size(backend: wgt::Backend) -> usize {
-    // TODO: this should be provided by the backend
-    match backend {
-        wgt::Backend::Empty => 0,
-        wgt::Backend::Vulkan => 64,
-        _ => unimplemented!(),
-    }
-}
-
-#[derive(Clone)]
-#[repr(C)]
-struct RawTlasInstance {
-    transform: [f32; 12],
-    custom_index_and_mask: u32,
-    shader_binding_table_record_offset_and_flags: u32,
-    acceleration_structure_reference: u64,
-}
-
-pub(crate) fn tlas_instance_into_bytes(
-    instance: &TlasInstance,
-    blas_address: u64,
-    backend: wgt::Backend,
-) -> Vec<u8> {
-    // TODO: get the device to do this
-    match backend {
-        wgt::Backend::Empty => vec![],
-        wgt::Backend::Vulkan => {
-            const MAX_U24: u32 = (1u32 << 24u32) - 1u32;
-            let temp = RawTlasInstance {
-                transform: *instance.transform,
-                custom_index_and_mask: (instance.custom_index & MAX_U24)
-                    | (u32::from(instance.mask) << 24),
-                shader_binding_table_record_offset_and_flags: 0,
-                acceleration_structure_reference: blas_address,
-            };
-            let temp: *const _ = &temp;
-            unsafe {
-                slice::from_raw_parts::<u8>(temp.cast::<u8>(), size_of::<RawTlasInstance>())
-                    .to_vec()
-            }
-        }
-        _ => unimplemented!(),
-    }
-}

wgpu-hal/src/dx12/adapter.rs

@@ -522,6 +522,8 @@ impl super::Adapter {
                     // Direct3D correctly bounds-checks all array accesses:
                     // https://microsoft.github.io/DirectX-Specs/d3d/archive/D3D11_3_FunctionalSpec.htm#18.6.8.2%20Device%20Memory%20Reads
                     uniform_bounds_check_alignment: wgt::BufferSize::new(1).unwrap(),
+                    raw_tlas_instance_size: 0,
+                    ray_tracing_scratch_buffer_alignment: 0,
                 },
                 downlevel,
             },

wgpu-hal/src/dx12/device.rs

@@ -21,6 +21,7 @@ use super::{conv, descriptor, D3D12Lib};
 use crate::{
     auxil::{self, dxgi::result::HResult},
     dx12::{borrow_optional_interface_temporarily, shader_compilation, Event},
+    TlasInstance,
 };
 
 // this has to match Naga's HLSL backend, and also needs to be null-terminated
@@ -1939,4 +1940,8 @@ impl crate::Device for super::Device {
             total_reserved_bytes: upstream.total_reserved_bytes,
         })
     }
+
+    fn tlas_instance_to_bytes(&self, _instance: TlasInstance) -> Vec<u8> {
+        todo!()
+    }
 }

wgpu-hal/src/dynamic/device.rs

@@ -5,7 +5,7 @@ use crate::{
     GetAccelerationStructureBuildSizesDescriptor, Label, MemoryRange, PipelineCacheDescriptor,
     PipelineCacheError, PipelineError, PipelineLayoutDescriptor, RenderPipelineDescriptor,
     SamplerDescriptor, ShaderError, ShaderInput, ShaderModuleDescriptor, TextureDescriptor,
-    TextureViewDescriptor,
+    TextureViewDescriptor, TlasInstance,
 };
 
 use super::{
@@ -158,6 +158,7 @@ pub trait DynDevice: DynResource {
         &self,
         acceleration_structure: Box<dyn DynAccelerationStructure>,
     );
+    fn tlas_instance_to_bytes(&self, instance: TlasInstance) -> Vec<u8>;
 
     fn get_internal_counters(&self) -> wgt::HalCounters;
     fn generate_allocator_report(&self) -> Option<wgt::AllocatorReport>;
@@ -520,6 +521,10 @@ impl<D: Device + DynResource> DynDevice for D {
         unsafe { D::destroy_acceleration_structure(self, acceleration_structure.unbox()) }
     }
 
+    fn tlas_instance_to_bytes(&self, instance: TlasInstance) -> Vec<u8> {
+        D::tlas_instance_to_bytes(self, instance)
+    }
+
     fn get_internal_counters(&self) -> wgt::HalCounters {
         D::get_internal_counters(self)
     }

wgpu-hal/src/empty.rs

@@ -1,5 +1,6 @@
 #![allow(unused_variables)]
 
+use crate::TlasInstance;
 use std::ops::Range;
 
 #[derive(Clone, Debug)]
@@ -306,6 +307,10 @@ impl crate::Device for Context {
     }
     unsafe fn destroy_acceleration_structure(&self, _acceleration_structure: Resource) {}
 
+    fn tlas_instance_to_bytes(&self, instance: TlasInstance) -> Vec<u8> {
+        vec![]
+    }
+
     fn get_internal_counters(&self) -> wgt::HalCounters {
         Default::default()
     }

wgpu-hal/src/gles/adapter.rs

@@ -851,6 +851,8 @@ impl super::Adapter {
                     // being, provide 1 as the value here, to cause as little
                     // trouble as possible.
                     uniform_bounds_check_alignment: wgt::BufferSize::new(1).unwrap(),
+                    raw_tlas_instance_size: 0,
+                    ray_tracing_scratch_buffer_alignment: 0,
                 },
             },
         })

wgpu-hal/src/gles/device.rs

@@ -8,7 +8,7 @@ use std::{
     sync::{Arc, Mutex},
 };
 
-use crate::AtomicFenceValue;
+use crate::{AtomicFenceValue, TlasInstance};
 use arrayvec::ArrayVec;
 use std::sync::atomic::Ordering;
 
@@ -1633,6 +1633,10 @@ impl crate::Device for super::Device {
     ) {
     }
 
+    fn tlas_instance_to_bytes(&self, _instance: TlasInstance) -> Vec<u8> {
+        unimplemented!()
+    }
+
     fn get_internal_counters(&self) -> wgt::HalCounters {
         self.counters.clone()
     }

wgpu-hal/src/lib.rs

@@ -971,6 +971,7 @@ pub trait Device: WasmNotSendSync {
         &self,
         acceleration_structure: <Self::A as Api>::AccelerationStructure,
     );
+    fn tlas_instance_to_bytes(&self, instance: TlasInstance) -> Vec<u8>;
 
     fn get_internal_counters(&self) -> wgt::HalCounters;
 
@@ -1771,6 +1772,12 @@ pub struct Alignments {
     /// [`Uniform`]: wgt::BufferBindingType::Uniform
     /// [size]: BufferBinding::size
     pub uniform_bounds_check_alignment: wgt::BufferSize,
+
+    /// The size of the raw TLAS instance
+    pub raw_tlas_instance_size: usize,
+
+    /// What the scratch buffer for building an acceleration structure must be aligned to
+    pub ray_tracing_scratch_buffer_alignment: u32,
 }
 
 #[derive(Clone, Debug)]
@@ -2519,3 +2526,11 @@ bitflags::bitflags! {
 pub struct AccelerationStructureBarrier {
     pub usage: Range<AccelerationStructureUses>,
 }
+
+#[derive(Debug, Copy, Clone)]
+pub struct TlasInstance {
+    pub transform: [f32; 12],
+    pub custom_index: u32,
+    pub mask: u8,
+    pub blas_address: u64,
+}

wgpu-hal/src/metal/adapter.rs

@@ -1001,6 +1001,8 @@ impl super::PrivateCapabilities {
                 // Metal Shading Language it generates, so from `wgpu_hal`'s
                 // users' point of view, references are tightly checked.
                 uniform_bounds_check_alignment: wgt::BufferSize::new(1).unwrap(),
+                raw_tlas_instance_size: 0,
+                ray_tracing_scratch_buffer_alignment: 0,
             },
             downlevel,
         }

wgpu-hal/src/metal/device.rs

@@ -8,6 +8,7 @@ use std::{
 
 use super::conv;
 use crate::auxil::map_naga_stage;
+use crate::TlasInstance;
 
 type DeviceResult<T> = Result<T, crate::DeviceError>;
 
@@ -1426,6 +1427,10 @@ impl crate::Device for super::Device {
         unimplemented!()
     }
 
+    fn tlas_instance_to_bytes(&self, _instance: TlasInstance) -> Vec<u8> {
+        unimplemented!()
+    }
+
     fn get_internal_counters(&self) -> wgt::HalCounters {
         self.counters.clone()
     }

wgpu-hal/src/vulkan/adapter.rs

@@ -1140,6 +1140,13 @@ impl PhysicalDeviceProperties {
                 };
                 wgt::BufferSize::new(alignment).unwrap()
             },
+            raw_tlas_instance_size: 64,
+            ray_tracing_scratch_buffer_alignment: self.acceleration_structure.map_or(
+                0,
+                |acceleration_structure| {
+                    acceleration_structure.min_acceleration_structure_scratch_offset_alignment
+                },
+            ),
         }
     }
 }

wgpu-hal/src/vulkan/device.rs

@@ -1,16 +1,18 @@
-use super::conv;
+use super::{conv, RawTlasInstance};
 
 use arrayvec::ArrayVec;
 use ash::{khr, vk};
 use parking_lot::Mutex;
 
+use crate::TlasInstance;
 use std::{
     borrow::Cow,
     collections::{hash_map::Entry, BTreeMap},
     ffi::{CStr, CString},
+    mem,
     mem::MaybeUninit,
     num::NonZeroU32,
-    ptr,
+    ptr, slice,
     sync::Arc,
 };
 
@@ -2557,6 +2559,22 @@ impl crate::Device for super::Device {
 
         self.counters.clone()
     }
+
+    fn tlas_instance_to_bytes(&self, instance: TlasInstance) -> Vec<u8> {
+        const MAX_U24: u32 = (1u32 << 24u32) - 1u32;
+        let temp = RawTlasInstance {
+            transform: instance.transform,
+            custom_index_and_mask: (instance.custom_index & MAX_U24)
+                | (u32::from(instance.mask) << 24),
+            shader_binding_table_record_offset_and_flags: 0,
+            acceleration_structure_reference: instance.blas_address,
+        };
+        let temp: *const _ = &temp;
+        unsafe {
+            slice::from_raw_parts::<u8>(temp.cast::<u8>(), mem::size_of::<RawTlasInstance>())
+                .to_vec()
+        }
+    }
 }
 
 impl super::DeviceShared {

wgpu-hal/src/vulkan/mod.rs

@@ -1423,3 +1423,12 @@ fn get_lost_err() -> crate::DeviceError {
     #[allow(unreachable_code)]
     crate::DeviceError::Lost
 }
+
+#[derive(Clone)]
+#[repr(C)]
+struct RawTlasInstance {
+    transform: [f32; 12],
+    custom_index_and_mask: u32,
+    shader_binding_table_record_offset_and_flags: u32,
+    acceleration_structure_reference: u64,
+}