Vulkan-Docs/chapters/VK_NV_ray_tracing/raytracing.txt

[[raytracing]]
= Ray Tracing

Unlike draw commands which use rasterization, ray tracing is a rendering
method which generates an image by tracing the path of rays which have a
single origin and using shaders to determine the final colour of an image
plane.

Ray tracing uses a separate rendering pipeline from both the graphics and
compute pipelines (see <<pipelines-raytracing,Ray tracing Pipeline>>).
It has a unique set of programmable and fixed function stages.

[[fig-raypipe]]
image::images/raypipe.svg[align="center",title="Ray tracing Pipeline",opts="{imageopts}"]

.Caption
****
Interaction between the different shader stages in the ray tracing pipeline
****


[[raytracing-commands]]
== Ray Tracing Commands
_Ray tracing commands_ provoke work in the raytacing pipeline.
Ray tracing commands are recorded into a command buffer and when executed by
a queue will produce work which executes according to the currently bound
ray tracing pipeline.
A ray tracing pipeline must: be bound to a command buffer before any ray
tracing commands are recorded in that command buffer.

Each ray tracing call operates on a set of shader stages that are specific
to the ray tracing pipeline as well as a set of
sname:VkAccelerationStructureNV objects which describe the scene geometry in
an implementation-specific way.
The relationship between the ray tracing pipeline object and the
acceleration structures is passed into the raytacing command in a
slink:VkBuffer object known as a _shader binding table_.

During execution, control alternates between scheduling and other
operations.
The scheduling functionality is implementation-specific and is responsible
for workload execution.
The shader stages are programmable.
_Traversal_, which refers to the process of traversing acceleration
structures to find potential intersections of rays with geometry, is fixed
function.

The programmable portions of the pipeline are exposed in a single-ray
programming model.
Each GPU thread handles one ray at a time.
Memory operations can be synchronized using standard memory barriers.
However, communication and synchronization between threads is not allowed.
In particular, the use of compute pipeline synchronization functions is not
supported in the ray tracing pipeline.

[open,refpage='vkCmdTraceRaysNV',desc='Initialize a ray tracing dispatch',type='protos']
--

To dispatch a ray tracing call use:

include::../../api/protos/vkCmdTraceRaysNV.txt[]

  * pname:commandBuffer is the command buffer into which the command will be
    recorded.
  * pname:raygenShaderBindingTableBuffer is the buffer object that holds the
    shader binding table data for the ray generation shader stage.
  * pname:raygenShaderBindingOffset is the offset in bytes (relative to
    pname:raygenShaderBindingTableBuffer) of the ray generation shader being
    used for the trace.
  * pname:missShaderBindingTableBuffer is the buffer object that holds the
    shader binding table data for the miss shader stage.
  * pname:missShaderBindingOffset is the offset in bytes (relative to
    pname:missShaderBindingTableBuffer) of the miss shader being used for
    the trace.
  * pname:missShaderBindingStride is the size in bytes of each shader
    binding table record in pname:missShaderBindingTableBuffer
  * pname:hitShaderBindingTableBuffer is the buffer object that holds the
    shader binding table data for the hit shader stages.
  * pname:hitShaderBindingOffset is the offset in bytes (relative to
    pname:hitShaderBindingTableBuffer) of the hit shader group being used
    for the trace.
  * pname:hitShaderBindingStride is the size in bytes of each shader binding
    table record in pname:hitShaderBindingTableBuffer
  * pname:callableShaderBindingTableBuffer is the buffer object that holds
    the shader binding table data for the callable shader stage.
  * pname:callableShaderBindingOffset is the offset in bytes (relative to
    pname:callableShaderBindingTableBuffer) of the callable shader being
    used for the trace.
  * pname:callableShaderBindingStride is the size in bytes of each shader
    binding table record in pname:callableShaderBindingTableBuffer
  * pname:width is the width of the ray trace query dimensions.
  * pname:height is height of the ray trace query dimensions.
  * pname:depth is depth of the ray trace query dimensions.

When the command is executed, a ray generation group of [eq]#pname:width
{times} pname:height {times} pname:depth# rays is assembled.

.Valid Usage
****
  * [[VUID-vkCmdTraceRaysNV-raygenShaderBindingOffset-02455]]
    pname:raygenShaderBindingOffset must: be less than the size of
    pname:raygenShaderBindingTableBuffer
  * [[VUID-vkCmdTraceRaysNV-raygenShaderBindingOffset-02456]]
    pname:raygenShaderBindingOffset must: be a multiple of
    sname:VkPhysicalDeviceRayTracingPropertiesNV::pname:shaderGroupBaseAlignment.
  * [[VUID-vkCmdTraceRaysNV-missShaderBindingOffset-02457]]
    pname:missShaderBindingOffset must: be less than the size of
    pname:missShaderBindingTableBuffer
  * [[VUID-vkCmdTraceRaysNV-missShaderBindingOffset-02458]]
    pname:missShaderBindingOffset must: be a multiple of
    sname:VkPhysicalDeviceRayTracingPropertiesNV::pname:shaderGroupBaseAlignment.
  * [[VUID-vkCmdTraceRaysNV-hitShaderBindingOffset-02459]]
    pname:hitShaderBindingOffset must: be less than the size of
    pname:hitShaderBindingTableBuffer
  * [[VUID-vkCmdTraceRaysNV-hitShaderBindingOffset-02460]]
    pname:hitShaderBindingOffset must: be a multiple of
    sname:VkPhysicalDeviceRayTracingPropertiesNV::pname:shaderGroupBaseAlignment.
  * [[VUID-vkCmdTraceRaysNV-callableShaderBindingOffset-02461]]
    pname:callableShaderBindingOffset must: be less than the size of
    pname:callableShaderBindingTableBuffer
  * [[VUID-vkCmdTraceRaysNV-callableShaderBindingOffset-02462]]
    pname:callableShaderBindingOffset must: be a multiple of
    sname:VkPhysicalDeviceRayTracingPropertiesNV::pname:shaderGroupBaseAlignment.
  * [[VUID-vkCmdTraceRaysNV-missShaderBindingStride-02463]]
    pname:missShaderBindingStride must: be a multiple of
    sname:VkPhysicalDeviceRayTracingPropertiesNV::pname:shaderGroupHandleSize
  * [[VUID-vkCmdTraceRaysNV-hitShaderBindingStride-02464]]
    pname:hitShaderBindingStride must: be a multiple of
    sname:VkPhysicalDeviceRayTracingPropertiesNV::pname:shaderGroupHandleSize
  * [[VUID-vkCmdTraceRaysNV-callableShaderBindingStride-02465]]
    pname:callableShaderBindingStride must: be a multiple of
    sname:VkPhysicalDeviceRayTracingPropertiesNV::pname:shaderGroupHandleSize
  * [[VUID-vkCmdTraceRaysNV-missShaderBindingStride-02466]]
    pname:missShaderBindingStride must: be a less than or equal to
    sname:VkPhysicalDeviceRayTracingPropertiesNV::pname:maxShaderGroupStride
  * [[VUID-vkCmdTraceRaysNV-hitShaderBindingStride-02467]]
    pname:hitShaderBindingStride must: be a less than or equal to
    sname:VkPhysicalDeviceRayTracingPropertiesNV::pname:maxShaderGroupStride
  * [[VUID-vkCmdTraceRaysNV-callableShaderBindingStride-02468]]
    pname:callableShaderBindingStride must: be a less than or equal to
    sname:VkPhysicalDeviceRayTracingPropertiesNV::pname:maxShaderGroupStride
  * [[VUID-vkCmdTraceRaysNV-width-02469]]
    pname:width must: be less than or equal to
    sname:VkPhysicalDeviceLimits::pname:maxComputeWorkGroupCount[0]
  * [[VUID-vkCmdTraceRaysNV-height-02470]]
    pname:height must: be less than or equal to
    sname:VkPhysicalDeviceLimits::pname:maxComputeWorkGroupCount[1]
  * [[VUID-vkCmdTraceRaysNV-depth-02471]]
    pname:depth must: be less than or equal to
    sname:VkPhysicalDeviceLimits::pname:maxComputeWorkGroupCount[2]
  * [[VUID-vkCmdTraceRaysNV-None-02472]]
    For each set _n_ that is statically used by the sname:VkPipeline bound
    to ename:VK_PIPELINE_BIND_POINT_RAY_TRACING_NV, a descriptor set must:
    have been bound to _n_ at ename:VK_PIPELINE_BIND_POINT_RAY_TRACING_NV,
    with a sname:VkPipelineLayout that is compatible for set _n_, with the
    sname:VkPipelineLayout used to create the current sname:VkPipeline, as
    described in <<descriptorsets-compatibility>>
  * [[VUID-vkCmdTraceRaysNV-None-02473]]
    Descriptors in each bound descriptor set, specified via
    fname:vkCmdBindDescriptorSets, must: be valid if they are statically
    used by the bound sname:VkPipeline object, specified via
    fname:vkCmdBindPipeline
  * [[VUID-vkCmdTraceRaysNV-None-02474]]
    A valid ray tracing pipeline must: be bound to the current command
    buffer with ename:VK_PIPELINE_BIND_POINT_RAY_TRACING_NV
  * [[VUID-vkCmdTraceRaysNV-None-02475]]
    For each push constant that is statically used by the sname:VkPipeline
    bound to ename:VK_PIPELINE_BIND_POINT_RAY_TRACING_NV, a push constant
    value must: have been set for
    ename:VK_PIPELINE_BIND_POINT_RAY_TRACING_NV, with a
    sname:VkPipelineLayout that is compatible for push constants with the
    one used to create the current sname:VkPipeline, as described in
    <<descriptorsets-compatibility>>
  * [[VUID-vkCmdTraceRaysNV-None-02476]]
    If any sname:VkSampler object that is accessed from a shader by the
    sname:VkPipeline bound to ename:VK_PIPELINE_BIND_POINT_RAY_TRACING_NV
    uses unnormalized coordinates, it must: not be used to sample from any
    sname:VkImage with a sname:VkImageView of the type
    ename:VK_IMAGE_VIEW_TYPE_3D, ename:VK_IMAGE_VIEW_TYPE_CUBE,
    ename:VK_IMAGE_VIEW_TYPE_1D_ARRAY, ename:VK_IMAGE_VIEW_TYPE_2D_ARRAY or
    ename:VK_IMAGE_VIEW_TYPE_CUBE_ARRAY, in any shader stage
  * [[VUID-vkCmdTraceRaysNV-None-02477]]
    If any sname:VkSampler object that is accessed from a shader by the
    sname:VkPipeline bound to ename:VK_PIPELINE_BIND_POINT_RAY_TRACING_NV
    uses unnormalized coordinates, it must: not be used with any of the
    SPIR-V `OpImageSample*` or `OpImageSparseSample*` instructions with
    code:ImplicitLod, code:Dref or code:Proj in their name, in any shader
    stage
  * [[VUID-vkCmdTraceRaysNV-None-02478]]
    If any sname:VkSampler object that is accessed from a shader by the
    sname:VkPipeline bound to ename:VK_PIPELINE_BIND_POINT_RAY_TRACING_NV
    uses unnormalized coordinates, it must: not be used with any of the
    SPIR-V `OpImageSample*` or `OpImageSparseSample*` instructions that
    includes a LOD bias or any offset values, in any shader stage
  * [[VUID-vkCmdTraceRaysNV-None-02479]]
    If the <<features-features-robustBufferAccess,robust buffer access>>
    feature is not enabled, and any shader stage in the sname:VkPipeline
    object bound to ename:VK_PIPELINE_BIND_POINT_RAY_TRACING_NV accesses a
    uniform buffer, it must: not access values outside of the range of that
    buffer specified in the bound descriptor set
  * [[VUID-vkCmdTraceRaysNV-None-02480]]
    If the <<features-features-robustBufferAccess,robust buffer access>>
    feature is not enabled, and any shader stage in the sname:VkPipeline
    object bound to ename:VK_PIPELINE_BIND_POINT_RAY_TRACING_NV accesses a
    storage buffer, it must: not access values outside of the range of that
    buffer specified in the bound descriptor set
  * [[VUID-vkCmdTraceRaysNV-None-02481]]
    If a sname:VkImageView is sampled with ename:VK_FILTER_LINEAR as a
    result of this command, then the image view's
    <<resources-image-view-format-features,format features>> must: contain
    ename:VK_FORMAT_FEATURE_SAMPLED_IMAGE_FILTER_LINEAR_BIT.
ifdef::VK_IMG_filter_cubic[]
  * [[VUID-vkCmdTraceRaysNV-None-02482]]
    If a sname:VkImageView is sampled with ename:VK_FILTER_CUBIC_IMG as a
    result of this command, then the image view's
    <<resources-image-view-format-features,format features>> must: contain
    ename:VK_FORMAT_FEATURE_SAMPLED_IMAGE_FILTER_CUBIC_BIT_IMG.
  * [[VUID-vkCmdTraceRaysNV-None-02483]]
    Any slink:VkImageView being sampled with ename:VK_FILTER_CUBIC_IMG as a
    result of this command must: not have a elink:VkImageViewType of
    ename:VK_IMAGE_VIEW_TYPE_3D, ename:VK_IMAGE_VIEW_TYPE_CUBE, or
    ename:VK_IMAGE_VIEW_TYPE_CUBE_ARRAY
endif::VK_IMG_filter_cubic[]
ifdef::VK_VERSION_1_1[]
  * [[VUID-vkCmdTraceRaysNV-commandBuffer-02484]]
    If pname:commandBuffer is an unprotected command buffer, and any
    pipeline stage in the sname:VkPipeline object bound to
    ename:VK_PIPELINE_BIND_POINT_RAY_TRACING_NV reads from or writes to any
    image or buffer, that image or buffer must: not be a protected image or
    protected buffer.
  * [[VUID-vkCmdTraceRaysNV-commandBuffer-02485]]
    If pname:commandBuffer is a protected command buffer, and any pipeline
    stage in the sname:VkPipeline object bound to
    ename:VK_PIPELINE_BIND_POINT_RAY_TRACING_NV writes to any image or
    buffer, that image or buffer must: not be an unprotected image or
    unprotected buffer.
  * [[VUID-vkCmdTraceRaysNV-commandBuffer-02486]]
    If pname:commandBuffer is a protected command buffer, and any pipeline
    stage other than the ray tracing pipeline stage in the sname:VkPipeline
    object bound to ename:VK_PIPELINE_BIND_POINT_RAY_TRACING_NV reads from
    any image or buffer, the image or buffer must: not be a protected image
    or protected buffer.
endif::VK_VERSION_1_1[]
ifdef::VK_NV_corner_sampled_image[]
  * [[VUID-vkCmdTraceRaysNV-flags-02487]]
    Any slink:VkImage created with a slink:VkImageCreateInfo::pname:flags
    containing ename:VK_IMAGE_CREATE_CORNER_SAMPLED_BIT_NV sampled as a
    result of this command must: only be sampled using a
    elink:VkSamplerAddressMode of
    ename:VK_SAMPLER_ADDRESS_MODE_CLAMP_TO_EDGE.
endif::VK_NV_corner_sampled_image[]
****

include::../../validity/protos/vkCmdTraceRaysNV.txt[]
--


[[shader-binding-table]]
== Shader Binding Table

A _shader binding table_ is a resource which establishes the relationship
between the ray tracing pipeline and the acceleration structures that were
built for the ray tracing query.
It indicates the shaders that operate on each geometry in an acceleration
structure.
In addition, it contains the resources accessed by each shader, including
indices of textures and constants.
The application allocates and manages _shader binding tables_ as
slink:VkBuffer objects.

Each entry in the shader binding table consists of
pname:shaderGroupHandleSize bytes of data as queried by
flink:vkGetRayTracingShaderGroupHandlesNV to refer to the shader that it
invokes.
The remainder of the data specified by the stride is application-visible
data that can be referenced by a shaderRecordNV block in the shader.

The shader binding tables to use in a ray tracing query are passed to
fname:vkCmdTraceRaysNV.
Shader binding tables are read-only in shaders that are executing on the ray
tracing pipeline.


[[shader-binding-table-indexing-rules]]
=== Indexing Rules

In order to execute the correct shaders and access the correct resources
during a ray tracing dispatch, the implementation must be able to locate
shader binding table entries at various stages of execution.
This is accomplished by defining a set of indexing rules that compute shader
binding table record positions relative to the buffer's base address in
memory.
The application must: organize the contents of the shader binding table's
memory in a way that application of the indexing rules will lead to correct
records.


==== Ray Generation Shaders

Only one ray generation shader is executed per ray tracing dispatch.
Its location is passed into fname:vkCmdTraceRaysNV using the
pname:raygenShaderBindingTableBuffer and
pname:raygenShaderBindingTableOffset parameters - there is no indexing.


==== Hit Shaders

The base for the computation of intersection, any hit and closest hit shader
locations is the pname:instanceShaderBindingTableRecordOffset value stored
with each instance of a top-level acceleration structure.
This value determines the beginning of the shader binding table records for
a given instance.
Each geometry in the instance must: have at least one hit program record.

In the following rule, _geometryIndex_ refers to the location of the
geometry within the instance.

The pname:sbtRecordStride and pname:sbtRecordOffset values are passed in as
parameters to code:traceNV() calls made in the shaders.
See Section 8.19 (Ray Tracing Functions) of the OpenGL Shading Language
Specification for more details.

The result of this computation is then added to
pname:hitProgramShaderBindingTableBaseIndex, a base index passed to
fname:vkCmdTraceRaysNV.

The complete rule to compute a hit shader binding table record index is:

 :: [eq]#instanceShaderBindingTableRecordOffset {plus}
      hitProgramShaderBindingTableBaseIndex {plus} geometryIndex {times}
      sbtRecordStride {plus} sbtRecordOffset#


==== Miss Shaders

A Miss shader is executed whenever a ray query fails to find an intersection
for the given scene geometry.
Multiple miss shaders can be executed throughout a ray tracing dispatch.

The base for the computation of miss shader locations is
pname:missProgramShaderBindingTableBaseIndex, a base index passed into
fname:vkCmdTraceRaysNV.

The pname:sbtRecordOffset value is passed in as parameters to code:traceNV()
calls made in the shaders.
See Section 8.19 (Ray Tracing Functions) of the OpenGL Shading Language
Specification for more details.

The complete rule to compute a miss shader binding table record address is:

 :: [eq]#missIndex {times} missShaderBindingStride {plus} sbtRecordOffset#


[[acceleration-structure]]
== Acceleration Structures

_Acceleration structures_ are data structures used by the implementation to
efficiently manage the scene geometry as it is traversed during a ray
tracing query.
The application is responsible for managing acceleration structure objects
(see <<resources-acceleration-structures,Acceleration Structures>>,
including allocation, destruction, executing builds or updates, and
synchronizing resources used uring ray tracing queries.

There are two types of acceleration structures, _top level acceleration
structures_ and _bottom level acceleration structures_.

[[fig-accelstruct]]
image::images/accelstruct.svg[align="center",title="Acceleration Structure",opts="{imageopts}"]

.Caption
****
The diagram shows the relationship between top and bottom level acceleration
structures.
****


[[acceleration-structure-instance]]
=== Instances

_Instances_ are found in top level acceleration structures and contain data
that refer to a single bottom-level acceleration structure, a transform
matrix, and shading information.
Multiple instances may point to a single bottom level acceleration
structure.

An instance is defined in a slink:VkBuffer by a structure consisting of 64
bytes of data.

  * pname:transform is 12 floats representing a 4x3 transform matrix in
    row-major order
  * pname:instanceCustomIndex The low 24 bits of a 32-bit integer after the
    transform.
    This value appears in the builtin code:gl_InstanceCustomIndexNV
  * pname:mask The high 8 bits of the same integer as instanceCustomIndex.
    This is the visibility mask.
    The instance can only be hit if rayMask & instance.mask != 0
  * pname:instanceOffset The low 24 bits of the next 32-bit integer.
    The value contributed by this instance to the hit shader binding table
    index computation as instanceShaderBindingTableRecordOffset.
  * pname:flags The high 8 bits of the same integer as instanceOffset.
    VkGeometryInstanceFlagBitsNV values that apply to this instance.
  * pname:accelerationStructure.
    The 8 byte value returned by vkGetAccelerationStructureHandleNV for the
    bottom level acceleration structure referred to by this instance.

[NOTE]
.Note
====
The C language spec doesn't define the ordering of bit-fields, but in
practice, this struct produces the layout described above:

[source,c]
---------------------------------------------------
struct VkGeometryInstanceNV {
    float          transform[12];
    uint32_t       instanceCustomIndex : 24;
    uint32_t       mask : 8;
    uint32_t       instanceOffset : 24;
    uint32_t       flags : 8;
    uint64_t       accelerationStructureHandle;
};
---------------------------------------------------

====

[open,refpage='VkGeometryInstanceFlagBitsNV',desc='Instance flag bits',type='enums']
--

Possible values of pname:flags in the instance modifying the behavior of
that instance are:,

include::../../api/enums/VkGeometryInstanceFlagBitsNV.txt[]

  * ename:VK_GEOMETRY_INSTANCE_TRIANGLE_CULL_DISABLE_BIT_NV disables face
    culling for this instance.
  * ename:VK_GEOMETRY_INSTANCE_TRIANGLE_FRONT_COUNTERCLOCKWISE_BIT_NV
    indicates that the front face of the triangle for culling purposes
    should be the face that's counter clockwise in object space relative to
    the ray origin.
    Because the facing is determined in object space, an instance transform
    matrix does not changing winding, but a geometry transform does.
  * ename:VK_GEOMETRY_INSTANCE_FORCE_OPAQUE_BIT_NV causes this instance to
    act as though ename:VK_GEOMETRY_OPAQUE_BIT_NV were specified on all
    geometries referenced by this instance.
    This behavior can be overridden by the ray flag
    code:gl_RayFlagsNoOpaqueNV.
  * ename:VK_GEOMETRY_INSTANCE_FORCE_NO_OPAQUE_BIT_NV causes this instance
    to act as though ename:VK_GEOMETRY_OPAQUE_BIT_NV were not specified on
    all geometries referenced by this instance.
    This behavior can be overridden by the ray flag
    code:gl_RayFlagsOpaqueNV.

ename:VK_GEOMETRY_INSTANCE_FORCE_NO_OPAQUE_BIT_NV and
ename:VK_GEOMETRY_INSTANCE_FORCE_OPAQUE_BIT_NV must: not be used in the same
flag.

--

[open,refpage='VkGeometryInstanceFlagsNV',desc='Bitmask of VkGeometryInstanceFlagBitsNV',type='flags']
--
include::../../api/flags/VkGeometryInstanceFlagsNV.txt[]

tname:VkGeometryInstanceFlagsNV is a bitmask type for setting a mask of zero
or more elink:VkGeometryInstanceFlagBitsNV.
--


[[acceleration-structure-geometry]]
=== Geometry

_Geometries_ refer to a triangle or axis-aligned bounding box.


[[acceleration-structure-top-level]]
=== Top Level Acceleration Structures

Opaque acceleration structure for an array of instances.
The descriptor referencing this is the starting point for tracing


[[acceleration-structure-bottom-level]]
=== Bottom Level Acceleration Structures

Opaque acceleration structure for an array of geometries.


[[acceleration-structure-building]]
=== Building Acceleration Structures

[open,refpage='vkCmdBuildAccelerationStructureNV',desc='Build an acceleration structure',type='protos']
--

To build an acceleration structure call:

include::../../api/protos/vkCmdBuildAccelerationStructureNV.txt[]

  * pname:commandBuffer is the command buffer into which the command will be
    recorded
  * pname:info contains the shared information for the acceleration
    structure's structure
  * pname:instanceData is the buffer containing instance data that will be
    used to build the acceleration structure as described in
    <<acceleration-structure-instance, Accelerator structure instances.>>
    This parameter must: be NULL for bottom level acceleration structures.
  * pname:instanceOffset is the offset in bytes (relative to the start of
    pname:instanceData) at which the instance data is located.
  * pname:update specifies whether to update the pname:dst acceleration
    structure with the data in pname:src.
  * pname:dst points to the target acceleration structure for the build.
  * pname:src points to an existing acceleration structure that can be used
    to update the pname:dst acceleration structure.
  * pname:scratch is the slink:VkBuffer that will be used as scratch memory
    for the build.
  * pname:scratchOffset is the offset in bytes relative to the start of
    pname:scratch that will be used as scratch memory.

.Valid Usage
****
  * [[VUID-vkCmdBuildAccelerationStructureNV-geometryCount-02241]]
    pname:geometryCount must: be less than or equal to
    sname:VkPhysicalDeviceRayTracingPropertiesNV::pname:maxGeometryCount
  * [[VUID-vkCmdBuildAccelerationStructureNV-dst-02488]]
    pname:dst must: have been created with compatible
    sname:VkAccelerationStructureInfoNV where
    sname:VkAccelerationStructureInfoNV:::pname:type and
    sname:VkAccelerationStructureInfoNV::pname:flags are identical,
    sname:VkAccelerationStructureInfoNV::pname:instanceCount and
    sname:VkAccelerationStructureInfoNV::pname:geometryCount for pname:dst
    are greater than or equal to the build size and each geometry in
    sname:VkAccelerationStructureInfoNV::pname:pGeometries for pname:dst has
    greater than or equal to the number of vertices, indices, and AABBs.
  * [[VUID-vkCmdBuildAccelerationStructureNV-update-02489]]
    If pname:update is true, pname:src must: not be ename:VK_NULL_HANDLE
  * [[VUID-vkCmdBuildAccelerationStructureNV-update-02490]]
    If pname:update is true, pname:src must: have been built last with
    ename:VK_BUILD_ACCELERATION_STRUCTURE_ALLOW_UPDATE_BIT_NV set in
    sname:VkAccelerationStructureInfoNV::pname:flags
  * [[VUID-vkCmdBuildAccelerationStructureNV-update-02491]]
    If pname:update is false, The pname:size member of the
    sname:VkMemoryRequirements structure returned from a call to
    fname:vkGetAccelerationStructureMemoryRequirementsNV with
    sname:VkAccelerationStructureMemoryRequirementsInfoNV::pname:accelerationStructure
    set to pname:dst and
    sname:VkAccelerationStructureMemoryRequirementsInfoNV::pname:type set to
    ename:VK_ACCELERATION_STRUCTURE_MEMORY_REQUIREMENTS_TYPE_BUILD_SCRATCH_NV
    must: be less than or equal to the size of pname:scratch minus
    pname:scratchOffset
  * [[VUID-vkCmdBuildAccelerationStructureNV-update-02492]]
    If pname:update is true, The pname:size member of the
    sname:VkMemoryRequirements structure returned from a call to
    fname:vkGetAccelerationStructureMemoryRequirementsNV with
    sname:VkAccelerationStructureMemoryRequirementsInfoNV::pname:accelerationStructure
    set to pname:dst and
    sname:VkAccelerationStructureMemoryRequirementsInfoNV::pname:type set to
    ename:VK_ACCELERATION_STRUCTURE_MEMORY_REQUIREMENTS_TYPE_UPDATE_SCRATCH_NV
    must: be less than or equal to the size of pname:scratch minus
    pname:scratchOffset
****

include::../../validity/protos/vkCmdBuildAccelerationStructureNV.txt[]
--


[[acceleration-structure-copying]]
=== Copying Acceleration Structures

An additional command exists for copying acceleration structures without
updating their contents.
The acceleration structure object may: be compacted in order to improve
performance.
Before copying, an application must: query the size of the resulting
acceleration structure.

[open,refpage='vkCmdWriteAccelerationStructuresPropertiesNV',desc='Write acceleration structure result parameters to query results.',type='protos']
--


To query acceleration structure size parameters call:

include::../../api/protos/vkCmdWriteAccelerationStructuresPropertiesNV.txt[]

  * pname:commandBuffer is the command buffer into which the command will be
    recorded.
  * pname:accelerationStructureCount is the count of acceleration structures
    for which to query the property.
  * pname:accelerationStructures points to an array of existing acceleration
    structures which have been built.
  * pname:queryType is a elink:VkQueryType value specifying the type of
    queries managed by the pool.
  * pname:queryPool is the query pool that will manage the results of the
    query.
  * pname:firstQuery is the first query index within the query pool that
    will contain the pname:accelerationStructureCount number of results

.Valid Usage
****
  * [[VUID-vkCmdWriteAccelerationStructuresPropertiesNV-queryType-02242]]
    pname:queryType must: be
    ename:VK_QUERY_TYPE_ACCELERATION_STRUCTURE_COMPACTED_SIZE_NV
  * [[VUID-vkCmdWriteAccelerationStructuresPropertiesNV-queryPool-02493]]
    pname:queryPool must: have been created with a pname:queryType matching
    pname:queryType
  * [[VUID-vkCmdWriteAccelerationStructuresPropertiesNV-queryPool-02494]]
    The queries identified by pname:queryPool and pname:firstQuery must: be
    _unavailable_
  * [[VUID-vkCmdWriteAccelerationStructuresPropertiesNV-accelerationStructures-02495]]
    All acceleration structures in pname:accelerationStructures must: have
    been built with
    ename:VK_BUILD_ACCELERATION_STRUCTURE_ALLOW_COMPACTION_BIT_NV if
    pname:queryType is
    ename:VK_QUERY_TYPE_ACCELERATION_STRUCTURE_COMPACTED_SIZE_NV
****

include::../../validity/protos/vkCmdWriteAccelerationStructuresPropertiesNV.txt[]

--


[open,refpage='vkCmdCopyAccelerationStructureNV',desc='Copy an acceleration structure',type='protos']
--

To copy an acceleration structure call:

include::../../api/protos/vkCmdCopyAccelerationStructureNV.txt[]

  * pname:commandBuffer is the command buffer into which the command will be
    recorded.
  * pname:dst points to the target acceleration structure for the copy
  * pname:src points to the source acceleration structure for the copy
  * pname:mode is a elink:VkCopyAccelerationStructureModeNV value that
    specifies additional operations to perform during the copy.

.Valid Usage
****
  * [[VUID-vkCmdCopyAccelerationStructureNV-mode-02496]]
    pname:mode must: be ename:VK_COPY_ACCELERATION_STRUCTURE_MODE_COMPACT_NV
    or ename:VK_COPY_ACCELERATION_STRUCTURE_MODE_CLONE_NV
  * [[VUID-vkCmdCopyAccelerationStructureNV-src-02497]]
    pname:src must: have been built with
    ename:VK_BUILD_ACCELERATION_STRUCTURE_ALLOW_COMPACTION_BIT_NV if
    pname:mode is ename:VK_COPY_ACCELERATION_STRUCTURE_MODE_COMPACT_NV
****

include::../../validity/protos/vkCmdCopyAccelerationStructureNV.txt[]

--

[open,refpage='VkCopyAccelerationStructureModeNV',desc='Acceleration structure copy mode',type='enums']
--

Possible values of flink:vkCmdCopyAccelerationStructureNV::pname:mode,
specifying additional operations to perform during the copy, are:

include::../../api/enums/VkCopyAccelerationStructureModeNV.txt[]

  * ename:VK_COPY_ACCELERATION_STRUCTURE_MODE_CLONE_NV creates a direct copy
    of the acceleration structure specified in pname:src into the one
    specified by pname:dst.
    The pname:dst acceleration structure must: have been created with the
    same parameters as pname:src.
  * ename:VK_COPY_ACCELERATION_STRUCTURE_MODE_COMPACT_NV creates a more
    compact version of an acceleration structure pname:src into pname:dst.
    The acceleration structure pname:dst must: have been created with a
    pname:compactedSize corresponding to the one returned by
    flink:vkCmdWriteAccelerationStructuresPropertiesNV after the build of
    the acceleration structure specified by pname:src.

--