Name Strings

SPV_NV_ray_tracing_motion_blur

Contact

See Issues list in the Khronos SPIRV-Registry repository: https://github.com/KhronosGroup/SPIRV-Registry

Contributors

  • Eric Werness, NVIDIA

  • Ashwin Lele, NVIDIA

  • Daniel Koch, NVIDIA

Status

  • Complete

Version

Last Modified Date

2023-11-29

Revision

2

Dependencies

This extension is written against the SPIR-V Specification, Version 1.5 Revision 5.

This extension requires SPIR-V 1.4.

This extension requires SPV_KHR_ray_tracing and interacts with SPV_NV_ray_tracing.

Overview

This extension adds new functionality to support the Vulkan VK_NV_ray_tracing_motion_blur extension in SPIR-V.

Extension Name

To use this extension within a SPIR-V module, the following OpExtension must be present in the module:

OpExtension "SPV_NV_ray_tracing_motion_blur"

New Capabilities

This extension introduces new capabilities:

RayTracingMotionBlurNV

New Builtins

Builtins added under the RayTracingMotionBlurNV capability

CurrentRayTimeNV

New Instructions

Instructions added under the RayTracingMotionBlurNV capability

OpTraceMotionNV
OpTraceRayMotionNV

Modifications to the SPIR-V Specification, Version 1.5

(Modify Section 3.21, Builtin, adding rows to the Builtin table)
Decoration Enabling Capabilities Extra Operands

5334

CurrentRayTimeNV
Provides the time parameter as passed to the parent OpTraceMotionNV or OpTraceRayMotionNV call Allowed only in IntersectionKHR, AnyHitKHR, ClosestHitKHR and MissKHR ray tracing execution models.

Refer to the Ray Tracing chapter of Vulkan API specification for more details.

RayTracingMotionBlurNV
(Modify Section 3.31, Capability, adding a row to the Capability table)
Capability Depends On Enabled by Extension

5341

RayTracingMotionBlurNV
Allows the use of OpTraceMotionNV or OpTraceRayMotionNV.

SPV_NV_ray_tracing_motion_blur
(Add a new sub section 3.32.24, Ray Tracing Instructions, adding to end of list of instructions)

OpTraceMotionNV

Trace a ray into the acceleration structure.

Acceleration Structure is the descriptor for the acceleration structure to trace into.

Ray Flags contains one or more of the Ray Flag values as described in SPV_KHR_ray_tracing.

Cull Mask is the mask to test against the instance mask.

SBT Offset and SBT Stride control indexing into the SBT for hit shaders called from this trace. SBT stands for Shader Binding Table. Refer to the Ray Tracing chapter of Vulkan API specification for details.

Miss Index is the index of the miss shader to be called from this trace call.

Ray Origin, Ray Tmin, Ray Direction, and Ray Tmax control the basic parameters of the ray to be traced.

Payload number matches the declared location of the payload structure to use for this trace.

Ray Flags, Cull Mask, SBT Offset, SBT Stride, and Miss Index must be a 32-bit integer type scalar.

Only the 8 least-significant bits of Cull Mask are used by this instruction - other bits are ignored.
Only the 4 least-significant bits of SBT Offset and SBT Stride are used by this instruction - other bits are ignored.
Only the 16 least-significant bits of Miss Index are used by this instruction - other bits are ignored.
Ray Origin and Ray Direction must be a 32-bit float type 3-component vector.

Ray Tmin and Ray Tmax must be a 32-bit float type scalar.

Current Time must be a 32-bit float type scalar.

This instruction is allowed only in RayGenerationKHR, ClosestHitKHR and MissKHR execution models.

This instruction is a shader call instruction which may invoke shaders with the IntersectionKHR, AnyHitKHR, ClosestHitKHR, and MissKHR execution models.

Capability:
RayTracingMotionBlurNV

13

5338

<id> Acceleration Structure

<id> Ray Flags

<id> Cull Mask

<id> SBT Offset

<id> SBT Stride

<id> Miss Index

<id> Ray Origin

<id> Ray Tmin

<id> Ray Direction

<id> Ray Tmax

<id> Current Time

<id> Payload number

OpTraceRayMotionNV

Trace a ray into the acceleration structure.

Acceleration Structure is the descriptor for the acceleration structure to trace into.

Ray Flags contains one or more of the Ray Flag values as described in SPV_KHR_ray_tracing.

Cull Mask is the mask to test against the instance mask.

SBT Offset and SBT Stride control indexing into the SBT for hit shaders called from this trace. SBT stands for Shader Binding Table. Refer to the Ray Tracing chapter of Vulkan API specification for details.

Miss Index is the index of the miss shader to be called from this trace call.

Ray Origin, Ray Tmin, Ray Direction, and Ray Tmax control the basic parameters of the ray to be traced.

Payload is a pointer to the ray payload structure to use for this trace. Payload must be the result of an OpVariable with a storage class of RayPayloadKHR or IncomingRayPayloadKHR.

Ray Flags, Cull Mask, SBT Offset, SBT Stride, and Miss Index must be a 32-bit integer type scalar.

Only the 8 least-significant bits of Cull Mask are used by this instruction - other bits are ignored.
Only the 4 least-significant bits of SBT Offset and SBT Stride are used by this instruction - other bits are ignored.
Only the 16 least-significant bits of Miss Index are used by this instruction - other bits are ignored.
Ray Origin and Ray Direction must be a 32-bit float type 3-component vector.

Ray Tmin and Ray Tmax must be a 32-bit float type scalar.

Current Time must be a 32-bit float type scalar.

This instruction is allowed only in RayGenerationKHR, ClosestHitKHR and MissKHR execution models.

This instruction is a shader call instruction which may invoke shaders with the IntersectionKHR, AnyHitKHR, ClosestHitKHR, and MissKHR execution models.

Capability:
RayTracingMotionBlurNV

13

5339

<id> Acceleration Structure

<id> Ray Flags

<id> Cull Mask

<id> SBT Offset

<id> SBT Stride

<id> Miss Index

<id> Ray Origin

<id> Ray Tmin

<id> Ray Direction

<id> Ray Tmax

<id> Current Time

<id> Payload

Validation Rules

An OpExtension must be added to the SPIR-V for validation layers to check legal use of this extension:

OpExtension "SPV_NV_ray_tracing_motion_blur"

Interactions with SPV_NV_ray_tracing

OpTypeAccelerationStructureKHR, RayGenerationKHR, IntersectionKHR, AnyHitKHR, ClosestHitKHR , MissKHR, RayPayloadKHR and IncomingRayPayloadKHR are aliases of OpTypeAccelerationStructureNV,RayGenerationNV, IntersectionNV, AnyHitNV, ClosestHitNV and MissNV respectively and can be used interchangeably in this extension.

OpTraceMotionNV is supported only if SPV_NV_ray_tracing is supported.

Issues

1) Why are there two separate instructions OpTraceMotionNV and OpTraceRayMotionNV added with this extension?

Resolved : OpTraceNV instruction in SPV_NV_ray_tracing extension has the last argument as payload id when compared to OpTraceRayKHR which has id of an OpVariable. We follow the same convention and provide two separate instructions. OpTraceMotionNV has payload id as the last argument and OpTraceRayMotionNV has id of an OpVariable.

Revision History

Rev Date Author Changes

1

2020-06-01

Ashwin Lele

Internal revisions

2

2023-11-29

Daniel Koch

fix typo in document title