Registered Extension Number

348

Revision

1

Extension and Version Dependencies

Contact

Other Extension Metadata

Last Modified Date

2020-11-12

Interactions and External Dependencies
Contributors
  • Matthäus Chajdas, AMD

  • Greg Grebe, AMD

  • Nicolai Hähnle, AMD

  • Tobias Hector, AMD

  • Dave Oldcorn, AMD

  • Skyler Saleh, AMD

  • Mathieu Robart, Arm

  • Marius Bjorge, Arm

  • Tom Olson, Arm

  • Sebastian Tafuri, EA

  • Henrik Rydgard, Embark

  • Juan Cañada, Epic Games

  • Patrick Kelly, Epic Games

  • Yuriy O’Donnell, Epic Games

  • Michael Doggett, Facebook/Oculus

  • Andrew Garrard, Imagination

  • Don Scorgie, Imagination

  • Dae Kim, Imagination

  • Joshua Barczak, Intel

  • Slawek Grajewski, Intel

  • Jeff Bolz, NVIDIA

  • Pascal Gautron, NVIDIA

  • Daniel Koch, NVIDIA

  • Christoph Kubisch, NVIDIA

  • Ashwin Lele, NVIDIA

  • Robert Stepinski, NVIDIA

  • Martin Stich, NVIDIA

  • Nuno Subtil, NVIDIA

  • Eric Werness, NVIDIA

  • Jon Leech, Khronos

  • Jeroen van Schijndel, OTOY

  • Juul Joosten, OTOY

  • Alex Bourd, Qualcomm

  • Roman Larionov, Qualcomm

  • David McAllister, Qualcomm

  • Spencer Fricke, Samsung

  • Lewis Gordon, Samsung

  • Ralph Potter, Samsung

  • Jasper Bekkers, Traverse Research

  • Jesse Barker, Unity

  • Baldur Karlsson, Valve

Description

Rasterization has been the dominant method to produce interactive graphics, but increasing performance of graphics hardware has made ray tracing a viable option for interactive rendering. Being able to integrate ray tracing with traditional rasterization makes it easier for applications to incrementally add ray traced effects to existing applications or to do hybrid approaches with rasterization for primary visibility and ray tracing for secondary queries.

To enable ray tracing, this extension adds a few different categories of new functionality:

  • A new ray tracing pipeline type with new shader domains: ray generation, intersection, any-hit, closest hit, miss, and callable

  • A shader binding indirection table to link shader groups with acceleration structure items

  • Ray tracing commands which initiate the ray pipeline traversal and invocation of the various new shader domains depending on which traversal conditions are met

This extension adds support for the following SPIR-V extension in Vulkan:

  • SPV_KHR_ray_tracing

New Enum Constants

  • VK_KHR_RAY_TRACING_PIPELINE_EXTENSION_NAME

  • VK_KHR_RAY_TRACING_PIPELINE_SPEC_VERSION

  • VK_SHADER_UNUSED_KHR

  • Extending VkBufferUsageFlagBits:

    • VK_BUFFER_USAGE_SHADER_BINDING_TABLE_BIT_KHR

  • Extending VkDynamicState:

    • VK_DYNAMIC_STATE_RAY_TRACING_PIPELINE_STACK_SIZE_KHR

  • Extending VkPipelineBindPoint:

    • VK_PIPELINE_BIND_POINT_RAY_TRACING_KHR

  • Extending VkPipelineCreateFlagBits:

    • VK_PIPELINE_CREATE_RAY_TRACING_NO_NULL_ANY_HIT_SHADERS_BIT_KHR

    • VK_PIPELINE_CREATE_RAY_TRACING_NO_NULL_CLOSEST_HIT_SHADERS_BIT_KHR

    • VK_PIPELINE_CREATE_RAY_TRACING_NO_NULL_INTERSECTION_SHADERS_BIT_KHR

    • VK_PIPELINE_CREATE_RAY_TRACING_NO_NULL_MISS_SHADERS_BIT_KHR

    • VK_PIPELINE_CREATE_RAY_TRACING_SHADER_GROUP_HANDLE_CAPTURE_REPLAY_BIT_KHR

    • VK_PIPELINE_CREATE_RAY_TRACING_SKIP_AABBS_BIT_KHR

    • VK_PIPELINE_CREATE_RAY_TRACING_SKIP_TRIANGLES_BIT_KHR

  • Extending VkPipelineStageFlagBits:

    • VK_PIPELINE_STAGE_RAY_TRACING_SHADER_BIT_KHR

  • Extending VkShaderStageFlagBits:

    • VK_SHADER_STAGE_ANY_HIT_BIT_KHR

    • VK_SHADER_STAGE_CALLABLE_BIT_KHR

    • VK_SHADER_STAGE_CLOSEST_HIT_BIT_KHR

    • VK_SHADER_STAGE_INTERSECTION_BIT_KHR

    • VK_SHADER_STAGE_MISS_BIT_KHR

    • VK_SHADER_STAGE_RAYGEN_BIT_KHR

  • Extending VkStructureType:

    • VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_RAY_TRACING_PIPELINE_FEATURES_KHR

    • VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_RAY_TRACING_PIPELINE_PROPERTIES_KHR

    • VK_STRUCTURE_TYPE_RAY_TRACING_PIPELINE_CREATE_INFO_KHR

    • VK_STRUCTURE_TYPE_RAY_TRACING_PIPELINE_INTERFACE_CREATE_INFO_KHR

    • VK_STRUCTURE_TYPE_RAY_TRACING_SHADER_GROUP_CREATE_INFO_KHR

Issues

(1) How does this extension differ from VK_NV_ray_tracing?

DISCUSSION:

The following is a summary of the main functional differences between VK_KHR_ray_tracing_pipeline and VK_NV_ray_tracing:

  • added support for indirect ray tracing (vkCmdTraceRaysIndirectKHR)

  • uses SPV_KHR_ray_tracing instead of SPV_NV_ray_tracing

    • refer to KHR SPIR-V enums instead of NV SPIR-V enums (which are functionally equivalent and aliased to the same values).

    • added RayGeometryIndexKHR built-in

  • removed vkCompileDeferredNV compilation functionality and replaced with deferred host operations interactions for ray tracing

  • added VkPhysicalDeviceRayTracingPipelineFeaturesKHR structure

  • extended VkPhysicalDeviceRayTracingPipelinePropertiesKHR structure

    • renamed maxRecursionDepth to maxRayRecursionDepth and it has a minimum of 1 instead of 31

    • require shaderGroupHandleSize to be 32 bytes

    • added maxRayDispatchInvocationCount, shaderGroupHandleAlignment and maxRayHitAttributeSize

  • reworked geometry structures so they could be better shared between device, host, and indirect builds

  • changed SBT parameters to a structure and added size (VkStridedDeviceAddressRegionKHR)

  • add parameter for requesting memory requirements for host and/or device build

  • added pipeline library support for ray tracing

  • added watertightness guarantees

  • added no-null-shader pipeline flags (VK_PIPELINE_CREATE_RAY_TRACING_NO_NULL_*_SHADERS_BIT_KHR)

  • added memory model interactions with ray tracing and define how subgroups work and can be repacked

(2) Can you give a more detailed comparision of differences and similarities between VK_NV_ray_tracing and VK_KHR_ray_tracing_pipeline?

DISCUSSION:

The following is a more detailed comparision of which commands, structures, and enums are aliased, changed, or removed.

(3) What are the changes between the public provisional (VK_KHR_ray_tracing v8) release and the internal provisional (VK_KHR_ray_tracing v9) release?

(4) What are the changes between the internal provisional (VK_KHR_ray_tracing v9) release and the final (VK_KHR_acceleration_structure v11 / VK_KHR_ray_tracing_pipeline v1) release?

  • refactor VK_KHR_ray_tracing into 3 extensions, enabling implementation flexibility and decoupling ray query support from ray pipelines:

  • Require Volatile for the following builtins in the ray generation, closest hit, miss, intersection, and callable shader stages:

    • SubgroupSize, SubgroupLocalInvocationId, SubgroupEqMask, SubgroupGeMask, SubgroupGtMask, SubgroupLeMask, SubgroupLtMask

    • SMIDNV, WarpIDNV

  • clarify buffer usage flags for ray tracing

    • VK_BUFFER_USAGE_SHADER_BINDING_TABLE_BIT_KHR is added as an alias of VK_BUFFER_USAGE_RAY_TRACING_BIT_NV and is required on shader binding table buffers

    • VK_BUFFER_USAGE_STORAGE_BUFFER_BIT is used in VK_KHR_acceleration_structure for scratchData

  • rename maxRecursionDepth to maxRayPipelineRecursionDepth (pipeline creation) and maxRayRecursionDepth (limit) to reduce confusion

  • Add queryable maxRayHitAttributeSize limit and rename members of VkRayTracingPipelineInterfaceCreateInfoKHR to maxPipelineRayPayloadSize and maxPipelineRayHitAttributeSize for clarity

  • Update SPIRV capabilities to use RayTracingKHR

  • extension is no longer provisional

  • define synchronization requirements for indirect trace rays and indirect buffer

(5) This extension adds gl_InstanceID for the intersection, any-hit, and closest hit shaders, but in KHR_vulkan_glsl, gl_InstanceID is replaced with gl_InstanceIndex. Which should be used for Vulkan in this extension?

RESOLVED: This extension uses gl_InstanceID and maps it to InstanceId in SPIR-V. It is acknowledged that this is different than other shader stages in Vulkan. There are two main reasons for the difference here:

  • symmetry with gl_PrimitiveID which is also available in these shaders

  • there is no “baseInstance” relevant for these shaders, and so ID makes it more obvious that this is zero-based.

Sample Code

Example ray generation GLSL shader

#version 450 core
#extension GL_EXT_ray_tracing : require
layout(set = 0, binding = 0, rgba8) uniform image2D image;
layout(set = 0, binding = 1) uniform accelerationStructureEXT as;
layout(location = 0) rayPayloadEXT float payload;

void main()
{
   vec4 col = vec4(0, 0, 0, 1);

   vec3 origin = vec3(float(gl_LaunchIDEXT.x)/float(gl_LaunchSizeEXT.x), float(gl_LaunchIDEXT.y)/float(gl_LaunchSizeEXT.y), 1.0);
   vec3 dir = vec3(0.0, 0.0, -1.0);

   traceRayEXT(as, 0, 0xff, 0, 1, 0, origin, 0.0, dir, 1000.0, 0);

   col.y = payload;

   imageStore(image, ivec2(gl_LaunchIDEXT.xy), col);
}

Version History

  • Revision 1, 2020-11-12 (Mathieu Robart, Daniel Koch, Eric Werness, Tobias Hector)

    • Decomposition of the specification, from VK_KHR_ray_tracing to VK_KHR_ray_tracing_pipeline (#1918,!3912)

    • require certain subgroup and sm_shader_builtin shader builtins to be decorated as volatile in the ray generation, closest hit, miss, intersection, and callable stages (#1924,!3903,!3954)

    • clarify buffer usage flags for ray tracing (#2181,!3939)

    • rename maxRecursionDepth to maxRayPipelineRecursionDepth and maxRayRecursionDepth (#2203,!3937)

    • add queriable maxRayHitAttributeSize and rename members of VkRayTracingPipelineInterfaceCreateInfoKHR (#2102,!3966)

    • update to use RayTracingKHR SPIR-V capability

    • add VUs for matching hit group type against geometry type (#2245,!3994)

    • require RayTMaxKHR be volatile in intersection shaders (#2268,!4030)

    • add numerical limits for ray parameters (#2235,!3960)

    • fix SBT indexing rules for device addresses (#2308,!4079)

    • relax formula for ray intersection candidate determination (#2322,!4080)

    • add more details on ShaderRecordBufferKHR variables (#2230,!4083)

    • clarify valid bits for InstanceCustomIndexKHR (GLSL/GLSL#19,!4128)

    • allow at most one IncomingRayPayloadKHR, IncomingCallableDataKHR, and HitAttributeKHR (!4129)

    • add minimum for maxShaderGroupStride (#2353,!4131)

    • require VK_KHR_pipeline_library extension to be supported (#2348,!4135)

    • clarify meaning of 'geometry index' (#2272,!4137)

    • restrict traces to TLAS (#2239,!4141)

    • add note about maxPipelineRayPayloadSize (#2383,!4172)

    • do not require raygen shader in pipeline libraries (!4185)

    • define sync for indirect trace rays and indirect buffer (#2407,!4208)

See Also

Document Notes

For more information, see the Vulkan Specification

This page is a generated document. Fixes and changes should be made to the generator scripts, not directly.

Copyright 2014-2021 The Khronos Group Inc.

SPDX-License-Identifier: CC-BY-4.0