Name Strings

SPV_NV_displacement_micromap

Contact

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

Contributors

  • Eric Werness, NVIDIA

  • Ashwin Lele, NVIDIA

  • Pyarelal Knowles, NVIDIA

  • Christoph Kubisch, NVIDIA

Status

  • Provisional

Version

Last Modified Date

2023-08-01

Revision

1

Dependencies

This extension is written against the SPIR-V Specification, Version 1.5 Revision 1.

This extension requires SPIR-V 1.4.

This extension interacts with SPV_KHR_ray_tracing, SPV_NV_mesh_shader, SPV_EXT_mesh_shader.

Overview

This extension adds new functionality to support the Vulkan VK_NV_displacement_micromap 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_displacement_micromap"

New Capabilities

This extension introduces new capabilities:

DisplacementMicromapNV
RayTracingDisplacementMicromapNV

New Builtins

Builtins added under the RayTracingDisplacementMicromapNV capability

HitMicroTriangleVertexPositionsNV
HitMicroTriangleVertexBarycentricsNV
HitKindFrontFacingMicroTriangleNV
HitKindBackFacingMicroTriangleNV

New Instructions

Instructions added under the DisplacementMicromapNV capability

OpFetchMicroTriangleVertexPositionNV
OpFetchMicroTriangleVertexBarycentricNV

Modifications to the SPIR-V Specification, Version 1.1

(Modify Section 2.2.2, Types )

add OpTypeAccelerationStructureNV to list of opaque types

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

5337

HitMicroTriangleVertexPositionsNV
The vertex positions for a hit with a microtriangle for the ray being traced.

Allowed in AnyHitKHR and ClosestHitKHR stages.

RayTracingDisplacementMicromapNV

5344

HitMicroTriangleVertexBarycentricsNV
The barycentric coordinates for vertices of a microtriangle hit for the ray being traced relative to the base triangle’s vertices.

Allowed in AnyHitKHR and ClosestHitKHR stages.

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

RayTracingDisplacementMicromapNV

5405

HitKindFrontFacingMicroTriangleNV
A link-time constant that HitKindKHR will return when OpTraceRayKHR intersects a front facing microtriangle.

Allowed in all stages.

RayTracingDisplacementMicromapNV

5406

HitKindBackFacingMicroTriangleNV
A link-time constant that HitKindKHR will return when OpTraceRayKHR intersects a back facing microtriangle.

Allowed in all stages.

RayTracingDisplacementMicromapNV
(Modify Section 3.HK, Hit Kinds, adding rows to the table)

3.HK, Hit Kinds

Values returned in the variable decorated as HitKindKHR from built-in intersections with triangle geometry.

Hit Kind Enabling Capabilities

builtin

HitKindFrontFacingMicroTriangleNV
The intersection was with front-facing displacement micromap geometry.

RayTracingDisplacementMicromapNV

builtin

HitKindBackFacingMicroTriangleKHR
The intersection was with back-facing displacement micromap geometry.

RayTracingDisplacementMicromapNV
(Modify Section 3.31, Capability, adding a row to the Capability table)
Capability Implicitly declares

5380

DisplacementMicromapNV
Uses the OpFetchMicroTriangleVertexPositionNV or OpFetchMicroTriangleVertexBarycentricNV instructions

Shader

5409

RayTracingDisplacementMicromapNV
Uses either of HitMicroTriangleVertexPositionsNV, HitMicroTriangleVertexBarycentricsNV, HitKindFrontFacingMicroTriangleNV, HitKindBackFacingMicroTriangleNV , HitKindFrontFacingMicroTriangleNV or HitKindBackFacingMicroTriangleKHR builtins

Shader
(Modify Section 3.32.6, Type-Declaration Instructions, adding a new table)

OpTypeAccelerationStructureKHR

Declares an acceleration structure type which is an opaque reference to acceleration structure handle as defined in the client API specification.

Consumed by OpFetchMicroTriangleVertexPositionNV and OpFetchMicroTriangleVertexBarycentricNV

This type is opaque: values of this type have no defined physical size or bit pattern.

Capability:
DisplacementMicromapNV

2

5341

<id> Result

Instructions

(Add the new instruction)

OpFetchMicroTriangleVertexPositionNV

Returns the vertex position of a micro triangle in object space.

Result Type must 3 component vector of 32-bit floating point type

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

Instance Id must be an <id> of 32-bit scalar integer type.

Geometry Index must be an <id> of 32-bit scalar integer type.

Primitive Index must be an <id> of 32-bit scalar integer type.

Barycentrics must be an <id> of 2 component vector of integer type.

This instruction is allowed only in RayGenerationKHR, MeshNV and GLCompute execution models.

Capability:
DisplacementMicromapNV

7

5300

<id> Result Type

Result <id>

<id> Acceleration Structure

<id> Instance Id

<id> Geometry Index

<id> Primitive Index

<id> Barycentrics

OpFetchMicroTriangleVertexBarycentricNV

Returns the barycentric coordinates of a micro triangle vertex relative to the base triangle vertices.

Result Type must 2 component vector of 32-bit floating point type

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

Instance Id must be an <id> of 32-bit scalar integer type.

Geometry Index must be an <id> of 32-bit scalar integer type.

Primitive Index must be an <id> of 32-bit scalar integer type.

Barycentrics must be an <id> of 2 component vector of integer type.

This instruction is allowed only in RayGenerationKHR, MeshNV and GLCompute execution models.

Capability:
DisplacementMicromapNV

7

5301

<id> Result Type

Result <id>

<id> Acceleration Structure

<id> Instance Id

<id> Geometry Index

<id> Primitive Index

<id> Barycentrics

Validation Rules

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

OpExtension "SPV_NV_displacement_micromap"

Issues

None yet!

Revision History

Rev Date Author Changes

1

2023-08-01

Pyarelal Knowles

Internal revisions