Vulkan-Docs/doc/specs/vulkan/chapters/descriptorsets.txt

// Copyright (c) 2015-2016 The Khronos Group Inc.
// Copyright notice at https://www.khronos.org/registry/speccopyright.html

[[descriptorsets]]
= Resource Descriptors

Shaders access buffer and image resources by using special shader variables
which are indirectly bound to buffer and image views via the API.
These variables are organized into sets, where each set of bindings is
represented by a _descriptor set_ object in the API and a descriptor set is
bound all at once.
A _descriptor_ is an opaque data structure representing a shader resource
such as a buffer view, image view, sampler, or combined image sampler.
The content of each set is determined by its _descriptor set layout_ and the
sequence of set layouts that can: be used by resource variables in shaders
within a pipeline is specified in a _pipeline layout_.

Each shader can: use up to pname:maxBoundDescriptorSets (see
<<features-limits, Limits>>) descriptor sets, and each descriptor set can:
include bindings for descriptors of all descriptor types.
Each shader resource variable is assigned a tuple of (set number, binding
number, array element) that defines its location within a descriptor set
layout.
In GLSL, the set number and binding number are assigned via layout
qualifiers, and the array element is implicitly assigned consecutively
starting with index equal to zero for the first element of an array (and
array element is zero for non-array variables):

.GLSL example
[source,{basebackend@docbook:c:glsl}]
---------------------------------------------------
// Assign set number = M, binding number = N, array element = 0
layout (set=M, binding=N) uniform sampler2D variableName;

// Assign set number = M, binding number = N for all array elements, and
// array element = I for the I'th member of the array.
layout (set=M, binding=N) uniform sampler2D variableNameArray[I];
---------------------------------------------------

.SPIR-V example
---------------------------------------------------
// Assign set number = M, binding number = N, array element = 0
               ...
          %1 = OpExtInstImport "GLSL.std.450"
               ...
               OpName %10 "variableName"
               OpDecorate %10 DescriptorSet M
               OpDecorate %10 Binding N
          %2 = OpTypeVoid
          %3 = OpTypeFunction %2
          %6 = OpTypeFloat 32
          %7 = OpTypeImage %6 2D 0 0 0 1 Unknown
          %8 = OpTypeSampledImage %7
          %9 = OpTypePointer UniformConstant %8
         %10 = OpVariable %9 UniformConstant
               ...

// Assign set number = M, binding number = N for all array elements, and
// array element = I for the I'th member of the array.
               ...
          %1 = OpExtInstImport "GLSL.std.450"
               ...
               OpName %13 "variableNameArray"
               OpDecorate %13 DescriptorSet M
               OpDecorate %13 Binding N
          %2 = OpTypeVoid
          %3 = OpTypeFunction %2
          %6 = OpTypeFloat 32
          %7 = OpTypeImage %6 2D 0 0 0 1 Unknown
          %8 = OpTypeSampledImage %7
          %9 = OpTypeInt 32 0
         %10 = OpConstant %9 I
         %11 = OpTypeArray %8 %10
         %12 = OpTypePointer UniformConstant %11
         %13 = OpVariable %12 UniformConstant
               ...
---------------------------------------------------


[[descriptorsets-types]]
== Descriptor Types

The following sections outline the various descriptor types supported by
Vulkan.
Each section defines a descriptor type, and each descriptor type has a
manifestation in the shading language and SPIR-V as well as in descriptor
sets.
There is mostly a one-to-one correspondence between descriptor types and
classes of opaque types in the shading language, where the opaque types in
the shading language must: refer to a descriptor in the pipeline layout of
the corresponding descriptor type.
But there is an exception to this rule as described in
<<descriptorsets-combinedimagesampler,Combined Image Sampler>>.


[[descriptorsets-storageimage]]
=== Storage Image

A _storage image_ (ename:VK_DESCRIPTOR_TYPE_STORAGE_IMAGE) is a descriptor
type that is used for load, store, and atomic operations on image memory
from within shaders bound to pipelines.

Loads from storage images do not use samplers and are unfiltered and do not
support coordinate wrapping or clamping.
Loads are supported in all shader stages for image formats which report
support for the
<<features-formats-properties,ename:VK_FORMAT_FEATURE_STORAGE_IMAGE_BIT>>
feature bit via flink:vkGetPhysicalDeviceFormatProperties.

Stores to storage images are supported in compute shaders for image formats
which report support for the ename:VK_FORMAT_FEATURE_STORAGE_IMAGE_BIT
feature.

Storage images also support atomic operations in compute shaders for image
formats which report support for the
<<features-formats-properties,ename:VK_FORMAT_FEATURE_STORAGE_IMAGE_ATOMIC_BIT>>
feature.

Load and store operations on storage images can: only be done on images in
ename:VK_IMAGE_LAYOUT_GENERAL layout.

When the <<features-features-fragmentStoresAndAtomics,
pname:fragmentStoresAndAtomics>> feature is enabled, stores and atomic
operations are also supported for storage images in fragment shaders with
the same set of image formats as supported in compute shaders.
When the <<features-features-vertexPipelineStoresAndAtomics,
pname:vertexPipelineStoresAndAtomics>> feature is enabled, stores and atomic
operations are also supported in vertex, tessellation, and geometry shaders
with the same set of image formats as supported in compute shaders.

Storage image declarations must: specify the image format in the shader if
the variable is used for atomic operations.

If the <<features-features-shaderStorageImageReadWithoutFormat,
pname:shaderStorageImageReadWithoutFormat>> feature is not enabled, storage
image declarations must: specify the image format in the shader if the
variable is used for load operations.

If the <<features-features-shaderStorageImageWriteWithoutFormat,
pname:shaderStorageImageWriteWithoutFormat>> feature is not enabled, storage
image declarations must: specify the image format in the shader if the
variable is used for store operations.

Storage images are declared in GLSL shader source using uniform code:image
variables of the appropriate dimensionality as well as a format layout
qualifier (if necessary):

.GLSL example
[source,{basebackend@docbook:c:glsl}]
---------------------------------------------------
layout (set=m, binding=n, r32f) uniform image2D myStorageImage;
---------------------------------------------------

.SPIR-V example
---------------------------------------------------
               ...
          %1 = OpExtInstImport "GLSL.std.450"
               ...
               OpName %9 "myStorageImage"
               OpDecorate %9 DescriptorSet m
               OpDecorate %9 Binding n
          %2 = OpTypeVoid
          %3 = OpTypeFunction %2
          %6 = OpTypeFloat 32
          %7 = OpTypeImage %6 2D 0 0 0 2 R32f
          %8 = OpTypePointer UniformConstant %7
          %9 = OpVariable %8 UniformConstant
               ...
---------------------------------------------------


[[descriptorsets-sampler]]
=== Sampler
A _sampler_ (ename:VK_DESCRIPTOR_TYPE_SAMPLER) represents a set of
parameters which control address calculations, filtering behavior, and other
properties, that can: be used to perform filtered loads from _sampled
images_ (see <<descriptorsets-sampledimage, Sampled Image>>).

Samplers are declared in GLSL shader source using uniform code:sampler
variables, where the sampler type has no associated texture dimensionality:

.GLSL Example
[source,{basebackend@docbook:c:glsl}]
---------------------------------------------------
layout (set=m, binding=n) uniform sampler mySampler;
---------------------------------------------------

.SPIR-V Example
---------------------------------------------------
               ...
          %1 = OpExtInstImport "GLSL.std.450"
               ...
               OpName %8 "mySampler"
               OpDecorate %8 DescriptorSet m
               OpDecorate %8 Binding n
          %2 = OpTypeVoid
          %3 = OpTypeFunction %2
          %6 = OpTypeSampler
          %7 = OpTypePointer UniformConstant %6
          %8 = OpVariable %7 UniformConstant
               ...
---------------------------------------------------


[[descriptorsets-sampledimage]]
=== Sampled Image

A _sampled image_ (ename:VK_DESCRIPTOR_TYPE_SAMPLED_IMAGE) can: be used
(usually in conjunction with a sampler) to retrieve sampled image data.
Shaders use a sampled image handle and a sampler handle to sample data,
where the image handle generally defines the shape and format of the memory
and the sampler generally defines how coordinate addressing is performed.
The same sampler can: be used to sample from multiple images, and it is
possible to sample from the same sampled image with multiple samplers, each
containing a different set of sampling parameters.

Sampled images are declared in GLSL shader source using uniform code:texture
variables of the appropriate dimensionality:

.GLSL example
[source,{basebackend@docbook:c:glsl}]
---------------------------------------------------
layout (set=m, binding=n) uniform texture2D mySampledImage;
---------------------------------------------------

.SPIR-V example
---------------------------------------------------
               ...
          %1 = OpExtInstImport "GLSL.std.450"
               ...
               OpName %9 "mySampledImage"
               OpDecorate %9 DescriptorSet m
               OpDecorate %9 Binding n
          %2 = OpTypeVoid
          %3 = OpTypeFunction %2
          %6 = OpTypeFloat 32
          %7 = OpTypeImage %6 2D 0 0 0 1 Unknown
          %8 = OpTypePointer UniformConstant %7
          %9 = OpVariable %8 UniformConstant
               ...
---------------------------------------------------


[[descriptorsets-combinedimagesampler]]
=== Combined Image Sampler

A _combined image sampler_ (ename:VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER)
represents a sampled image along with a set of sampling parameters.
It is logically considered a sampled image and a sampler bound together.

[NOTE]
.Note
====
On some implementations, it may: be more efficient to sample from an image
using a combination of sampler and sampled image that are stored together in
the descriptor set in a combined descriptor.
====

Combined image samplers are declared in GLSL shader source using uniform
code:sampler variables of the appropriate dimensionality:

.GLSL example
[source,{basebackend@docbook:c:glsl}]
---------------------------------------------------
layout (set=m, binding=n) uniform sampler2D myCombinedImageSampler;
---------------------------------------------------

.SPIR-V example
---------------------------------------------------
               ...
          %1 = OpExtInstImport "GLSL.std.450"
               ...
               OpName %10 "myCombinedImageSampler"
               OpDecorate %10 DescriptorSet m
               OpDecorate %10 Binding n
          %2 = OpTypeVoid
          %3 = OpTypeFunction %2
          %6 = OpTypeFloat 32
          %7 = OpTypeImage %6 2D 0 0 0 1 Unknown
          %8 = OpTypeSampledImage %7
          %9 = OpTypePointer UniformConstant %8
         %10 = OpVariable %9 UniformConstant
               ...
---------------------------------------------------

ename:VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER descriptor set entries can:
also be accessed via separate sampler and sampled image shader variables.
Such variables refer exclusively to the corresponding half of the
descriptor, and can: be combined in the shader with samplers or sampled
images that can: come from the same descriptor or from other combined or
separate descriptor types.
There are no additional restrictions on how a separate sampler or sampled
image variable is used due to it originating from a combined descriptor.


[[descriptorsets-uniformtexelbuffer]]
=== Uniform Texel Buffer

A _uniform texel buffer_ (ename:VK_DESCRIPTOR_TYPE_UNIFORM_TEXEL_BUFFER)
represents a tightly packed array of homogeneous formatted data that is
stored in a buffer and is made accessible to shaders.
Uniform texel buffers are read-only.

Uniform texel buffers are declared in GLSL shader source using uniform
code:samplerBuffer variables:

.GLSL example
[source,{basebackend@docbook:c:glsl}]
---------------------------------------------------
layout (set=m, binding=n) uniform samplerBuffer myUniformTexelBuffer;
---------------------------------------------------

.SPIR-V example
---------------------------------------------------
               ...
          %1 = OpExtInstImport "GLSL.std.450"
               ...
               OpName %10 "myUniformTexelBuffer"
               OpDecorate %10 DescriptorSet m
               OpDecorate %10 Binding n
          %2 = OpTypeVoid
          %3 = OpTypeFunction %2
          %6 = OpTypeFloat 32
          %7 = OpTypeImage %6 Buffer 0 0 0 1 Unknown
          %8 = OpTypeSampledImage %7
          %9 = OpTypePointer UniformConstant %8
         %10 = OpVariable %9 UniformConstant
               ...
---------------------------------------------------


[[descriptorsets-storagetexelbuffer]]
=== Storage Texel Buffer

A _storage texel buffer_ (ename:VK_DESCRIPTOR_TYPE_STORAGE_TEXEL_BUFFER)
represents a tightly packed array of homogeneous formatted data that is
stored in a buffer and is made accessible to shaders.
Storage texel buffers differ from uniform texel buffers in that they support
stores and atomic operations in shaders, may: support a different maximum
length, and may: have different performance characteristics.

Storage texel buffers are declared in GLSL shader source using uniform
code:imageBuffer variables:

.GLSL example
[source,{basebackend@docbook:c:glsl}]
---------------------------------------------------
layout (set=m, binding=n, r32f) uniform imageBuffer myStorageTexelBuffer;
---------------------------------------------------

.SPIR-V example
---------------------------------------------------
               ...
          %1 = OpExtInstImport "GLSL.std.450"
               ...
               OpName %9 "myStorageTexelBuffer"
               OpDecorate %9 DescriptorSet m
               OpDecorate %9 Binding n
          %2 = OpTypeVoid
          %3 = OpTypeFunction %2
          %6 = OpTypeFloat 32
          %7 = OpTypeImage %6 Buffer 0 0 0 2 R32f
          %8 = OpTypePointer UniformConstant %7
          %9 = OpVariable %8 UniformConstant
               ...
---------------------------------------------------


[[descriptorsets-uniformbuffer]]
=== Uniform Buffer

A _uniform buffer_ (ename:VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER) is a region of
structured storage that is made accessible for read-only access to shaders.
It is typically used to store medium sized arrays of constants such as
shader parameters, matrices and other related data.

Uniform buffers are declared in GLSL shader source using the uniform storage
qualifier and block syntax:

.GLSL example
[source,{basebackend@docbook:c:glsl}]
---------------------------------------------------
layout (set=m, binding=n) uniform myUniformBuffer
{
    vec4 myElement[32];
};
---------------------------------------------------

.SPIR-V example
---------------------------------------------------
               ...
          %1 = OpExtInstImport "GLSL.std.450"
               ...
               OpName %11 "myUniformBuffer"
               OpMemberName %11 0 "myElement"
               OpName %13 ""
               OpDecorate %10 ArrayStride 16
               OpMemberDecorate %11 0 Offset 0
               OpDecorate %11 Block
               OpDecorate %13 DescriptorSet m
               OpDecorate %13 Binding n
          %2 = OpTypeVoid
          %3 = OpTypeFunction %2
          %6 = OpTypeFloat 32
          %7 = OpTypeVector %6 4
          %8 = OpTypeInt 32 0
          %9 = OpConstant %8 32
         %10 = OpTypeArray %7 %9
         %11 = OpTypeStruct %10
         %12 = OpTypePointer Uniform %11
         %13 = OpVariable %12 Uniform
               ...
---------------------------------------------------


[[descriptorsets-storagebuffer]]
=== Storage Buffer

A _storage buffer_ (ename:VK_DESCRIPTOR_TYPE_STORAGE_BUFFER) is a region of
structured storage that supports both read and write access for shaders.
In addition to general read and write operations, some members of storage
buffers can: be used as the target of atomic operations.
In general, atomic operations are only supported on members that have
unsigned integer formats.

Storage buffers are declared in GLSL shader source using buffer storage
qualifier and block syntax:

.GLSL example
[source,{basebackend@docbook:c:glsl}]
---------------------------------------------------
layout (set=m, binding=n) buffer myStorageBuffer
{
    vec4 myElement[];
};
---------------------------------------------------

.SPIR-V example
---------------------------------------------------
               ...
          %1 = OpExtInstImport "GLSL.std.450"
               ...
               OpName %9 "myStorageBuffer"
               OpMemberName %9 0 "myElement"
               OpName %11 ""
               OpDecorate %8 ArrayStride 16
               OpMemberDecorate %9 0 Offset 0
               OpDecorate %9 BufferBlock
               OpDecorate %11 DescriptorSet m
               OpDecorate %11 Binding n
          %2 = OpTypeVoid
          %3 = OpTypeFunction %2
          %6 = OpTypeFloat 32
          %7 = OpTypeVector %6 4
          %8 = OpTypeRuntimeArray %7
          %9 = OpTypeStruct %8
         %10 = OpTypePointer Uniform %9
         %11 = OpVariable %10 Uniform
               ...
---------------------------------------------------


[[descriptorsets-uniformbufferdynamic]]
=== Dynamic Uniform Buffer

A _dynamic uniform buffer_ (ename:VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER_DYNAMIC)
differs from a uniform buffer only in how its address and length are
specified.
Uniform buffers bind a buffer address and length that is specified in the
descriptor set update by a buffer handle, offset and range (see
<<descriptorsets-updates, Descriptor Set Updates>>).
With dynamic uniform buffers the buffer handle, offset and range specified
in the descriptor set define the base address and length.
The dynamic offset which is relative to this base address is taken from the
pname:pDynamicOffsets parameter to flink:vkCmdBindDescriptorSets (see
<<descriptorsets-binding, Descriptor Set Binding>>).
The address used for a dynamic uniform buffer is the sum of the buffer base
address and the relative offset.
The length is unmodified and remains the range as specified in the
descriptor update.
The shader syntax is identical for uniform buffers and dynamic uniform
buffers.


[[descriptorsets-storagebufferdynamic]]
=== Dynamic Storage Buffer

A _dynamic storage buffer_ (ename:VK_DESCRIPTOR_TYPE_STORAGE_BUFFER_DYNAMIC)
differs from a storage buffer only in how its address and length are
specified.
The difference is identical to the difference between uniform buffers and
dynamic uniform buffers (see <<descriptorsets-uniformbufferdynamic, Dynamic
Uniform Buffer>>).
The shader syntax is identical for storage buffers and dynamic storage
buffers.


[[descriptorsets-inputattachment]]
=== Input Attachment

An _input attachment_ (ename:VK_DESCRIPTOR_TYPE_INPUT_ATTACHMENT) is an
image view that can: be used for pixel local load operations from within
fragment shaders bound to pipelines.
Loads from input attachments are unfiltered.
All image formats that are supported for color attachments
(ename:VK_FORMAT_FEATURE_COLOR_ATTACHMENT_BIT) or depth/stencil attachments
(ename:VK_FORMAT_FEATURE_DEPTH_STENCIL_ATTACHMENT_BIT) for a given image
tiling mode are also supported for input attachments.

In the shader, input attachments must: be decorated with their input
attachment index in addition to descriptor set and binding numbers.

.GLSL example
[source,{basebackend@docbook:c:glsl}]
---------------------------------------------------
layout (input_attachment_index=i, set=m, binding=n) uniform subpassInput myInputAttachment;
---------------------------------------------------

.SPIR-V example
---------------------------------------------------
               ...
          %1 = OpExtInstImport "GLSL.std.450"
               ...
               OpName %9 "myInputAttachment"
               OpDecorate %9 DescriptorSet m
               OpDecorate %9 Binding n
               OpDecorate %9 InputAttachmentIndex i
          %2 = OpTypeVoid
          %3 = OpTypeFunction %2
          %6 = OpTypeFloat 32
          %7 = OpTypeImage %6 SubpassData 0 0 0 2 Unknown
          %8 = OpTypePointer UniformConstant %7
          %9 = OpVariable %8 UniformConstant
               ...
---------------------------------------------------


[[descriptorsets-sets]]
== Descriptor Sets

Descriptors are grouped together into descriptor set objects.
A descriptor set object is an opaque object that contains storage for a set
of descriptors, where the types and number of descriptors is defined by a
descriptor set layout.
The layout object may: be used to define the association of each descriptor
binding with memory or other hardware resources.
The layout is used both for determining the resources that need to be
associated with the descriptor set, and determining the interface between
shader stages and shader resources.


[[descriptorsets-setlayout]]
=== Descriptor Set Layout

// refBegin VkDescriptorSetLayout Opaque handle to a descriptor set layout object

A descriptor set layout object is defined by an array of zero or more
descriptor bindings.
Each individual descriptor binding is specified by a descriptor type, a
count (array size) of the number of descriptors in the binding, a set of
shader stages that can: access the binding, and (if using immutable
samplers) an array of sampler descriptors.

Descriptor set layout objects are represented by sname:VkDescriptorSetLayout
handles:

include::../api/handles/VkDescriptorSetLayout.txt[]

// refEnd VkDescriptorSetLayout

// refBegin vkCreateDescriptorSetLayout Create a new descriptor set layout

To create descriptor set layout objects, call:

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

  * pname:device is the logical device that creates the descriptor set
    layout.
  * pname:pCreateInfo is a pointer to an instance of the
    slink:VkDescriptorSetLayoutCreateInfo structure specifying the state of
    the descriptor set layout object.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.
  * pname:pSetLayout points to a sname:VkDescriptorSetLayout handle in which
    the resulting descriptor set layout object is returned.

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

// refBegin VkDescriptorSetLayoutCreateInfo Structure specifying parameters of a newly created descriptor set layout

Information about the descriptor set layout is passed in an instance of the
sname:VkDescriptorSetLayoutCreateInfo structure:

include::../api/structs/VkDescriptorSetLayoutCreateInfo.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to an extension-specific structure.
  * pname:flags is reserved for future use.
  * pname:bindingCount is the number of elements in pname:pBindings.
  * pname:pBindings is a pointer to an array of
    slink:VkDescriptorSetLayoutBinding structures.

include::../validity/structs/VkDescriptorSetLayoutCreateInfo.txt[]

// refBegin VkDescriptorSetLayoutBinding Structure specifying a descriptor set layout binding

The sname:VkDescriptorSetLayoutBinding structure is defined as:

include::../api/structs/VkDescriptorSetLayoutBinding.txt[]

  * pname:binding is the binding number of this entry and corresponds to a
    resource of the same binding number in the shader stages.
  * pname:descriptorType is a elink:VkDescriptorType specifying which type
    of resource descriptors are used for this binding.
  * pname:descriptorCount is the number of descriptors contained in the
    binding, accessed in a shader as an array.
    If pname:descriptorCount is zero this binding entry is reserved and the
    resource must: not be accessed from any stage via this binding within
    any pipeline using the set layout.
  * pname:stageFlags member is a bitmask of elink:VkShaderStageFlagBits
    specifying which pipeline shader stages can: access a resource for this
    binding.
    ename:VK_SHADER_STAGE_ALL is a shorthand specifying that all defined
    shader stages, including any additional stages defined by extensions,
    can: access the resource.
+
--
If a shader stage is not included in pname:stageFlags, then a resource must:
not be accessed from that stage via this binding within any pipeline using
the set layout.
There are no limitations on what combinations of stages can: be used by a
descriptor binding, and in particular a binding can: be used by both
graphics stages and the compute stage.
--
  * pname:pImmutableSamplers affects initialization of samplers.
    If pname:descriptorType specifies a ename:VK_DESCRIPTOR_TYPE_SAMPLER or
    ename:VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER type descriptor, then
    pname:pImmutableSamplers can: be used to initialize a set of _immutable
    samplers_.
    Immutable samplers are permanently bound into the set layout; later
    binding a sampler into an immutable sampler slot in a descriptor set is
    not allowed.
    If pname:pImmutableSamplers is not `NULL`, then it is considered to be a
    pointer to an array of sampler handles that will be consumed by the set
    layout and used for the corresponding binding.
    If pname:pImmutableSamplers is `NULL`, then the sampler slots are
    dynamic and sampler handles must: be bound into descriptor sets using
    this layout.
    If pname:descriptorType is not one of these descriptor types, then
    pname:pImmutableSamplers is ignored.

The above layout definition allows the descriptor bindings to be specified
sparsely such that not all binding numbers between 0 and the maximum binding
number need to be specified in the pname:pBindings array.
However, all binding numbers between 0 and the maximum binding number may:
consume memory in the descriptor set layout even if not all descriptor
bindings are used, though it should: not consume additional memory from the
descriptor pool.

[NOTE]
.Note
====
The maximum binding number specified should: be as compact as possible to
avoid wasted memory.
====

include::../validity/structs/VkDescriptorSetLayoutBinding.txt[]

The following examples show a shader snippet using two descriptor sets, and
application code that creates corresponding descriptor set layouts.

.GLSL example
[source,{basebackend@docbook:c:glsl}]
---------------------------------------------------
//
// binding to a single sampled image descriptor in set 0
//
layout (set=0, binding=0) uniform texture2D mySampledImage;

//
// binding to an array of sampled image descriptors in set 0
//
layout (set=0, binding=1) uniform texture2D myArrayOfSampledImages[12];

//
// binding to a single uniform buffer descriptor in set 1
//
layout (set=1, binding=0) uniform myUniformBuffer
{
    vec4 myElement[32];
};
---------------------------------------------------

.SPIR-V example
---------------------------------------------------
               ...
          %1 = OpExtInstImport "GLSL.std.450"
               ...
               OpName %9 "mySampledImage"
               OpName %14 "myArrayOfSampledImages"
               OpName %18 "myUniformBuffer"
               OpMemberName %18 0 "myElement"
               OpName %20 ""
               OpDecorate %9 DescriptorSet 0
               OpDecorate %9 Binding 0
               OpDecorate %14 DescriptorSet 0
               OpDecorate %14 Binding 1
               OpDecorate %17 ArrayStride 16
               OpMemberDecorate %18 0 Offset 0
               OpDecorate %18 Block
               OpDecorate %20 DescriptorSet 1
               OpDecorate %20 Binding 0
          %2 = OpTypeVoid
          %3 = OpTypeFunction %2
          %6 = OpTypeFloat 32
          %7 = OpTypeImage %6 2D 0 0 0 1 Unknown
          %8 = OpTypePointer UniformConstant %7
          %9 = OpVariable %8 UniformConstant
         %10 = OpTypeInt 32 0
         %11 = OpConstant %10 12
         %12 = OpTypeArray %7 %11
         %13 = OpTypePointer UniformConstant %12
         %14 = OpVariable %13 UniformConstant
         %15 = OpTypeVector %6 4
         %16 = OpConstant %10 32
         %17 = OpTypeArray %15 %16
         %18 = OpTypeStruct %17
         %19 = OpTypePointer Uniform %18
         %20 = OpVariable %19 Uniform
               ...
---------------------------------------------------

.API example
[source,{basebackend@docbook:c++:cpp}]
-------------------------------------------------------------------------------
VkResult myResult;

const VkDescriptorSetLayoutBinding myDescriptorSetLayoutBinding[] =
{
    // binding to a single image descriptor
    {
        0,                                      // binding
        VK_DESCRIPTOR_TYPE_SAMPLED_IMAGE,       // descriptorType
        1,                                      // descriptorCount
        VK_SHADER_STAGE_FRAGMENT_BIT,           // stageFlags
        NULL                                    // pImmutableSamplers
    },

    // binding to an array of image descriptors
    {
        1,                                      // binding
        VK_DESCRIPTOR_TYPE_SAMPLED_IMAGE,       // descriptorType
        12,                                     // descriptorCount
        VK_SHADER_STAGE_FRAGMENT_BIT,           // stageFlags
        NULL                                    // pImmutableSamplers
    },

    // binding to a single uniform buffer descriptor
    {
        0,                                      // binding
        VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER,      // descriptorType
        1,                                      // descriptorCount
        VK_SHADER_STAGE_FRAGMENT_BIT,           // stageFlags
        NULL                                    // pImmutableSamplers
    }
};

const VkDescriptorSetLayoutCreateInfo myDescriptorSetLayoutCreateInfo[] =
{
    // Create info for first descriptor set with two descriptor bindings
    {
        VK_STRUCTURE_TYPE_DESCRIPTOR_SET_LAYOUT_CREATE_INFO,    // sType
        NULL,                                                   // pNext
        0,                                                      // flags
        2,                                                      // bindingCount
        &myDescriptorSetLayoutBinding[0]                        // pBindings
    },

    // Create info for second descriptor set with one descriptor binding
    {
        VK_STRUCTURE_TYPE_DESCRIPTOR_SET_LAYOUT_CREATE_INFO,    // sType
        NULL,                                                   // pNext
        0,                                                      // flags
        1,                                                      // bindingCount
        &myDescriptorSetLayoutBinding[2]                        // pBindings
    }
};

VkDescriptorSetLayout myDescriptorSetLayout[2];

//
// Create first descriptor set layout
//
myResult = vkCreateDescriptorSetLayout(
    myDevice,
    &myDescriptorSetLayoutCreateInfo[0],
    NULL,
    &myDescriptorSetLayout[0]);

//
// Create second descriptor set layout
//
myResult = vkCreateDescriptorSetLayout(
    myDevice,
    &myDescriptorSetLayoutCreateInfo[1],
    NULL,
    &myDescriptorSetLayout[1]);
-------------------------------------------------------------------------------

// refBegin vkDestroyDescriptorSetLayout Destroy a descriptor set layout object

To destroy a descriptor set layout, call:

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

  * pname:device is the logical device that destroys the descriptor set
    layout.
  * pname:descriptorSetLayout is the descriptor set layout to destroy.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.

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


[[descriptorsets-pipelinelayout]]
=== Pipeline Layouts

// refBegin VkPipelineLayout Opaque handle to a pipeline layout object

Access to descriptor sets from a pipeline is accomplished through a
_pipeline layout_.
Zero or more descriptor set layouts and zero or more push constant ranges
are combined to form a pipeline layout object which describes the complete
set of resources that can: be accessed by a pipeline.
The pipeline layout represents a sequence of descriptor sets with each
having a specific layout.
This sequence of layouts is used to determine the interface between shader
stages and shader resources.
Each pipeline is created using a pipeline layout.

Pipeline layout objects are represented by sname:VkPipelineLayout handles:

include::../api/handles/VkPipelineLayout.txt[]

// refEnd VkPipelineLayout

// refBegin vkCreatePipelineLayout Creates a new pipeline layout object

To create a pipeline layout, call:

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

  * pname:device is the logical device that creates the pipeline layout.
  * pname:pCreateInfo is a pointer to an instance of the
    slink:VkPipelineLayoutCreateInfo structure specifying the state of the
    pipeline layout object.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.
  * pname:pPipelineLayout points to a sname:VkPipelineLayout handle in which
    the resulting pipeline layout object is returned.

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

// refBegin VkPipelineLayoutCreateInfo Structure specifying the parameters of a newly created pipeline layout object

The slink:VkPipelineLayoutCreateInfo structure is defined as:

include::../api/structs/VkPipelineLayoutCreateInfo.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to an extension-specific structure.
  * pname:flags is reserved for future use.
  * pname:setLayoutCount is the number of descriptor sets included in the
    pipeline layout.
  * pname:pSetLayouts is a pointer to an array of
    sname:VkDescriptorSetLayout objects.
  * pname:pushConstantRangeCount is the number of push constant ranges
    included in the pipeline layout.
  * pname:pPushConstantRanges is a pointer to an array of
    sname:VkPushConstantRange structures defining a set of push constant
    ranges for use in a single pipeline layout.
    In addition to descriptor set layouts, a pipeline layout also describes
    how many push constants can: be accessed by each stage of the pipeline.
+
[NOTE]
.Note
====
Push constants represent a high speed path to modify constant data in
pipelines that is expected to outperform memory-backed resource updates.
====

include::../validity/structs/VkPipelineLayoutCreateInfo.txt[]

// refBegin VkPushConstantRange Structure specifying a push constant range

The sname:VkPushConstantRange structure is defined as:

include::../api/structs/VkPushConstantRange.txt[]

  * pname:stageFlags is a set of stage flags describing the shader stages
    that will access a range of push constants.
    If a particular stage is not included in the range, then accessing
    members of that range of push constants from the corresponding shader
    stage will result in undefined data being read.
  * pname:offset and pname:size are the start offset and size, respectively,
    consumed by the range.
    Both pname:offset and pname:size are in units of bytes and must: be a
    multiple of 4.
    The layout of the push constant variables is specified in the shader.

include::../validity/structs/VkPushConstantRange.txt[]

Once created, pipeline layouts are used as part of pipeline creation (see
<<pipelines, Pipelines>>), as part of binding descriptor sets (see
<<descriptorsets-binding, Descriptor Set Binding>>), and as part of setting
push constants (see <<descriptorsets-push-constants, Push Constant
Updates>>).
Pipeline creation accepts a pipeline layout as input, and the layout may: be
used to map (set, binding, arrayElement) tuples to hardware resources or
memory locations within a descriptor set.
The assignment of hardware resources depends only on the bindings defined in
the descriptor sets that comprise the pipeline layout, and not on any shader
source.

[[descriptorsets-pipelinelayout-consistency]]
All resource variables <<shaders-staticuse,statically used>> in all shaders
in a pipeline must: be declared with a (set,binding,arrayElement) that
exists in the corresponding descriptor set layout and is of an appropriate
descriptor type and includes the set of shader stages it is used by in
pname:stageFlags.
The pipeline layout can: include entries that are not used by a particular
pipeline, or that are dead-code eliminated from any of the shaders.
The pipeline layout allows the application to provide a consistent set of
bindings across multiple pipeline compiles, which enables those pipelines to
be compiled in a way that the implementation may: cheaply switch pipelines
without reprogramming the bindings.

Similarly, the push constant block declared in each shader (if present)
must: only place variables at offsets that are each included in a push
constant range with pname:stageFlags including the bit corresponding to the
shader stage that uses it.
The pipeline layout can: include ranges or portions of ranges that are not
used by a particular pipeline, or for which the variables have been
dead-code eliminated from any of the shaders.

There is a limit on the total number of resources of each type that can: be
included in bindings in all descriptor set layouts in a pipeline layout as
shown in <<descriptorsets-pipelinelayout-limits,Pipeline Layout Resource
Limits>>.
The ``Total Resources Available'' column gives the limit on the number of
each type of resource that can: be included in bindings in all descriptor
sets in the pipeline layout.
Some resource types count against multiple limits.
Additionally, there are limits on the total number of each type of resource
that can: be used in any pipeline stage as described in
<<interfaces-resources-limits,Shader Resource Limits>>.

[[descriptorsets-pipelinelayout-limits]]
.Pipeline Layout Resource Limits
[width="80%",cols="<37,<22",options="header"]
|====
| Total Resources Available | Resource Types
.2+<.^| maxDescriptorSetSamplers
            | sampler           | combined image sampler
.3+<.^| maxDescriptorSetSampledImages
            | sampled image     | combined image sampler | uniform texel buffer
.2+<.^| maxDescriptorSetStorageImages
            | storage image     | storage texel buffer
.2+<.^| maxDescriptorSetUniformBuffers
            | uniform buffer    | uniform buffer dynamic
| maxDescriptorSetUniformBuffersDynamic
            | uniform buffer dynamic
.2+<.^| maxDescriptorSetStorageBuffers
            | storage buffer    | storage buffer dynamic
| maxDescriptorSetStorageBuffersDynamic
            | storage buffer dynamic
| maxDescriptorSetInputAttachments
            | input attachment
|====


// refBegin vkDestroyPipelineLayout Destroy a pipeline layout object

To destroy a pipeline layout, call:

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

  * pname:device is the logical device that destroys the pipeline layout.
  * pname:pipelineLayout is the pipeline layout to destroy.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.

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


[[descriptorsets-compatibility]]
==== Pipeline Layout Compatibility

Two pipeline layouts are defined to be ``compatible for
<<descriptorsets-push-constants, push constants>>'' if they were created
with identical push constant ranges.
Two pipeline layouts are defined to be ``compatible for set N'' if they were
created with matching (the same, or identically defined) descriptor set
layouts for sets zero through N, and if they were created with identical
push constant ranges.

When binding a descriptor set (see <<descriptorsets-binding, Descriptor Set
Binding>>) to set number N, if the previously bound descriptor sets for sets
zero through N-1 were all bound using compatible pipeline layouts, then
performing this binding does not disturb any of the lower numbered sets.
If, additionally, the previous bound descriptor set for set N was bound
using a pipeline layout compatible for set N, then the bindings in sets
numbered greater than N are also not disturbed.

Similarly, when binding a pipeline, the pipeline can: correctly access any
previously bound descriptor sets which were bound with compatible pipeline
layouts, as long as all lower numbered sets were also bound with compatible
layouts.

Layout compatibility means that descriptor sets can: be bound to a command
buffer for use by any pipeline created with a compatible pipeline layout,
and without having bound a particular pipeline first.
It also means that descriptor sets can: remain valid across a pipeline
change, and the same resources will be accessible to the newly bound
pipeline.

ifdef::implementation-guide[]
.Implementor's Note
****
A consequence of layout compatibility is that when the implementation
compiles a pipeline layout and assigns hardware units to resources, the
mechanism to assign hardware units for set N should: only be a function of
sets [0..N].
****
endif::implementation-guide[]

[NOTE]
.Note
====
Place the least frequently changing descriptor sets near the start of the
pipeline layout, and place the descriptor sets representing the most
frequently changing resources near the end.
When pipelines are switched, only the descriptor set bindings that have been
invalidated will need to be updated and the remainder of the descriptor set
bindings will remain in place.
====

The maximum number of descriptor sets that can: be bound to a pipeline
layout is queried from physical device properties (see
pname:maxBoundDescriptorSets in <<features-limits, Limits>>).

.API example
[source,{basebackend@docbook:c++:cpp}]
---------------------------------------------------
const VkDescriptorSetLayout layouts[] = { layout1, layout2 };

const VkPushConstantRange ranges[] =
{
    {
        VK_PIPELINE_STAGE_VERTEX_SHADER_BIT,    // stageFlags
        0,                                      // offset
        4                                       // size
    },

    {
        VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT,  // stageFlags
        4,                                      // offset
        4                                       // size
    },
};

const VkPipelineLayoutCreateInfo createInfo =
{
    VK_STRUCTURE_TYPE_PIPELINE_LAYOUT_CREATE_INFO,  // sType
    NULL,                                           // pNext
    0,                                              // flags
    2,                                              // setLayoutCount
    layouts,                                        // pSetLayouts
    2,                                              // pushConstantRangeCount
    ranges                                          // pPushConstantRanges
};

VkPipelineLayout myPipelineLayout;
myResult = vkCreatePipelineLayout(
    myDevice,
    &createInfo,
    NULL,
    &myPipelineLayout);
---------------------------------------------------


[[descriptorsets-allocation]]
=== Allocation of Descriptor Sets

// refBegin VkDescriptorPool Opaque handle to a descriptor pool object

A _descriptor pool_ maintains a pool of descriptors, from which descriptor
sets are allocated.
Descriptor pools are externally synchronized, meaning that the application
must: not allocate and/or free descriptor sets from the same pool in
multiple threads simultaneously.

Descriptor pools are represented by sname:VkDescriptorPool handles:

include::../api/handles/VkDescriptorPool.txt[]

// refEnd VkDescriptorPool

// refBegin vkCreateDescriptorPool Creates a descriptor pool object

To create a descriptor pool object, call:

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

  * pname:device is the logical device that creates the descriptor pool.
  * pname:pCreateInfo is a pointer to an instance of the
    slink:VkDescriptorPoolCreateInfo structure specifying the state of the
    descriptor pool object.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.
  * pname:pDescriptorPool points to a sname:VkDescriptorPool handle in which
    the resulting descriptor pool object is returned.

pname:pAllocator controls host memory allocation as described in the
<<memory-allocation, Memory Allocation>> chapter.

The created descriptor pool is returned in pname:pDescriptorPool.

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

// refBegin VkDescriptorPoolCreateInfo Structure specifying parameters of a newly created descriptor pool

Additional information about the pool is passed in an instance of the
sname:VkDescriptorPoolCreateInfo structure:

include::../api/structs/VkDescriptorPoolCreateInfo.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to an extension-specific structure.
  * pname:flags specifies certain supported operations on the pool.
    Bits which can: be set include:
+
--
// refBegin VkDescriptorPoolCreateFlagBits Bitmask specifying certain supported operations on a descriptor pool
include::../api/enums/VkDescriptorPoolCreateFlagBits.txt[]
--
+
If pname:flags includes
ename:VK_DESCRIPTOR_POOL_CREATE_FREE_DESCRIPTOR_SET_BIT, then descriptor
sets can: return their individual allocations to the pool, i.e.
all of fname:vkAllocateDescriptorSets, fname:vkFreeDescriptorSets, and
fname:vkResetDescriptorPool are allowed.
Otherwise, descriptor sets allocated from the pool must: not be individually
freed back to the pool, i.e.
only fname:vkAllocateDescriptorSets and fname:vkResetDescriptorPool are
allowed.
+
  * pname:maxSets is the maximum number of descriptor sets that can: be
    allocated from the pool.
  * pname:poolSizeCount is the number of elements in pname:pPoolSizes.
  * pname:pPoolSizes is a pointer to an array of sname:VkDescriptorPoolSize
    structures, each containing a descriptor type and number of descriptors
    of that type to be allocated in the pool.

If multiple sname:VkDescriptorPoolSize structures appear in the
pname:pPoolSizes array then the pool will be created with enough storage for
the total number of descriptors of each type.

Fragmentation of a descriptor pool is possible and may: lead to descriptor
set allocation failures.
A failure due to fragmentation is defined as failing a descriptor set
allocation despite the sum of all outstanding descriptor set allocations
from the pool plus the requested allocation requiring no more than the total
number of descriptors requested at pool creation.
Implementations provide certain guarantees of when fragmentation must: not
cause allocation failure, as described below.

If a descriptor pool has not had any descriptor sets freed since it was
created or most recently reset then fragmentation must: not cause an
allocation failure (note that this is always the case for a pool created
without the ename:VK_DESCRIPTOR_POOL_CREATE_FREE_DESCRIPTOR_SET_BIT bit
set).
Additionally, if all sets allocated from the pool since it was created or
most recently reset use the same number of descriptors (of each type) and
the requested allocation also uses that same number of descriptors (of each
type), then fragmentation must: not cause an allocation failure.

If an allocation failure occurs due to fragmentation, an application can:
create an additional descriptor pool to perform further descriptor set
allocations.

include::../validity/structs/VkDescriptorPoolCreateInfo.txt[]

// refBegin VkDescriptorPoolSize Structure specifying descriptor pool size

The sname:VkDescriptorPoolSize structure is defined as:

include::../api/structs/VkDescriptorPoolSize.txt[]

  * pname:type is the type of descriptor.
  * pname:descriptorCount is the number of descriptors of that type to
    allocate.

include::../validity/structs/VkDescriptorPoolSize.txt[]

// refBegin vkDestroyDescriptorPool Destroy a descriptor pool object

To destroy a descriptor pool, call:

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

  * pname:device is the logical device that destroys the descriptor pool.
  * pname:descriptorPool is the descriptor pool to destroy.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.

When a pool is destroyed, all descriptor sets allocated from the pool are
implicitly freed and become invalid.
Descriptor sets allocated from a given pool do not need to be freed before
destroying that descriptor pool.

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

// refBegin VkDescriptorSet Opaque handle to a descriptor set object

Descriptor sets are allocated from descriptor pool objects, and are
represented by sname:VkDescriptorSet handles:

include::../api/handles/VkDescriptorSet.txt[]

// refEnd VkDescriptorSet

// refBegin vkAllocateDescriptorSets Allocate one or more descriptor sets

To allocate descriptor sets from a descriptor pool, call:

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

  * pname:device is the logical device that owns the descriptor pool.
  * pname:pAllocateInfo is a pointer to an instance of the
    slink:VkDescriptorSetAllocateInfo structure describing parameters of the
    allocation.
  * pname:pDescriptorSets is a pointer to an array of sname:VkDescriptorSet
    handles in which the resulting descriptor set objects are returned.
    The array must: be at least the length specified by the
    pname:descriptorSetCount member of pname:pAllocateInfo.

The allocated descriptor sets are returned in pname:pDescriptorSets.

When a descriptor set is allocated, the initial state is largely
uninitialized and all descriptors are undefined.
However, the descriptor set can: be bound in a command buffer without
causing errors or exceptions.
All entries that are statically used by a pipeline in a drawing or
dispatching command must: have been populated before the descriptor set is
bound for use by that command.
Entries that are not statically used by a pipeline can: have uninitialized
descriptors or descriptors of resources that have been destroyed, and
executing a draw or dispatch with such a descriptor set bound does not cause
undefined behavior.
This means applications need not populate unused entries with dummy
descriptors.

If an allocation fails due to fragmentation, an indeterminate error is
returned with an unspecified error code.
Any returned error other than ename:VK_ERROR_FRAGMENTED_POOL does not imply
its usual meaning: applications should: assume that the allocation failed
due to fragmentation, and create a new descriptor pool.

[NOTE]
.Note
====
Applications should: check for a negative return value when allocating new
descriptor sets, assume that any error effectively means
ename:VK_ERROR_FRAGMENTED_POOL, and try to create a new descriptor pool.
If ename:VK_ERROR_FRAGMENTED_POOL is the actual return value, it adds
certainty to that decision.

The reason for this is that ename:VK_ERROR_FRAGMENTED_POOL was only added in
a later revision of the 1.0 specification, and so drivers may: return other
errors if they were written against earlier revisions.
To ensure full compatibility with earlier patch revisions, these other
errors are allowed.
====

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

// refBegin VkDescriptorSetAllocateInfo Structure specifying the allocation parameters for descriptor sets

The sname:VkDescriptorSetAllocateInfo structure is defined as:

include::../api/structs/VkDescriptorSetAllocateInfo.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to an extension-specific structure.
  * pname:descriptorPool is the pool which the sets will be allocated from.
  * pname:descriptorSetCount determines the number of descriptor sets to be
    allocated from the pool.
  * pname:pSetLayouts is an array of descriptor set layouts, with each
    member specifying how the corresponding descriptor set is allocated.

include::../validity/structs/VkDescriptorSetAllocateInfo.txt[]

// refBegin vkFreeDescriptorSets Free one or more descriptor sets

To free allocated descriptor sets, call:

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

  * pname:device is the logical device that owns the descriptor pool.
  * pname:descriptorPool is the descriptor pool from which the descriptor
    sets were allocated.
  * pname:descriptorSetCount is the number of elements in the
    pname:pDescriptorSets array.
  * pname:pDescriptorSets is an array of handles to sname:VkDescriptorSet
    objects.

After a successful call to fname:vkFreeDescriptorSets, all descriptor sets
in pname:pDescriptorSets are invalid.

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

// refBegin vkResetDescriptorPool Resets a descriptor pool object

To return all descriptor sets allocated from a given pool to the pool,
rather than freeing individual descriptor sets, call:

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

  * pname:device is the logical device that owns the descriptor pool.
  * pname:descriptorPool is the descriptor pool to be reset.
  * pname:flags is reserved for future use.

Resetting a descriptor pool recycles all of the resources from all of the
descriptor sets allocated from the descriptor pool back to the descriptor
pool, and the descriptor sets are implicitly freed.

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


[[descriptorsets-updates]]
=== Descriptor Set Updates

// refBegin vkUpdateDescriptorSets Update the contents of a descriptor set object

Once allocated, descriptor sets can: be updated with a combination of write
and copy operations.
To update descriptor sets, call:

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

  * pname:device is the logical device that updates the descriptor sets.
  * pname:descriptorWriteCount is the number of elements in the
    pname:pDescriptorWrites array.
  * pname:pDescriptorWrites is a pointer to an array of
    slink:VkWriteDescriptorSet structures describing the descriptor sets to
    write to.
  * pname:descriptorCopyCount is the number of elements in the
    pname:pDescriptorCopies array.
  * pname:pDescriptorCopies is a pointer to an array of
    slink:VkCopyDescriptorSet structures describing the descriptor sets to
    copy between.

The operations described by pname:pDescriptorWrites are performed first,
followed by the operations described by pname:pDescriptorCopies.
Within each array, the operations are performed in the order they appear in
the array.

Each element in the pname:pDescriptorWrites array describes an operation
updating the descriptor set using descriptors for resources specified in the
structure.

Each element in the pname:pDescriptorCopies array is a
slink:VkCopyDescriptorSet structure describing an operation copying
descriptors between sets.

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

// refBegin VkWriteDescriptorSet Structure specifying the parameters of a descriptor set write operation

The sname:VkWriteDescriptorSet structure is defined as:

include::../api/structs/VkWriteDescriptorSet.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to an extension-specific structure.
  * pname:dstSet is the destination descriptor set to update.
  * pname:dstBinding is the descriptor binding within that set.
  * pname:dstArrayElement is the starting element in that array.
  * pname:descriptorCount is the number of descriptors to update (the number
    of elements in pname:pImageInfo, pname:pBufferInfo, or
    pname:pTexelBufferView).
  * pname:descriptorType is a elink:VkDescriptorType specifying the type of
    each descriptor in pname:pImageInfo, pname:pBufferInfo, or
    pname:pTexelBufferView, as described below.
    It must: be the same type as that specified in
    sname:VkDescriptorSetLayoutBinding for pname:dstSet at pname:dstBinding.
    The type of the descriptor also controls which array the descriptors are
    taken from.
  * pname:pImageInfo points to an array of slink:VkDescriptorImageInfo
    structures or is ignored, as described below.
  * pname:pBufferInfo points to an array of slink:VkDescriptorBufferInfo
    structures or is ignored, as described below.
  * pname:pTexelBufferView points to an array of slink:VkBufferView handles
    as described in the <<resources-buffer-views,Buffer Views>> section or
    is ignored, as described below.

Only one of pname:pImageInfo, pname:pBufferInfo, or pname:pTexelBufferView
members is used according to the descriptor type specified in the
pname:descriptorType member of the containing sname:VkWriteDescriptorSet
structure, as specified below.

[[descriptorsets-updates-consecutive, consecutive binding updates]]
If the pname:dstBinding has fewer than pname:descriptorCount array elements
remaining starting from pname:dstArrayElement, then the remainder will be
used to update the subsequent binding - pname:dstBinding+1 starting at array
element zero.
This behavior applies recursively, with the update affecting consecutive
bindings as needed to update all pname:descriptorCount descriptors.
All consecutive bindings updated via a single sname:VkWriteDescriptorSet
structure must: have identical pname:descriptorType and pname:stageFlags,
and must: all either use immutable samplers or must: all not use immutable
samplers.

include::../validity/structs/VkWriteDescriptorSet.txt[]

// refBegin VkDescriptorType Specifies the type of a descriptor in a descriptor set

The type of descriptors in a descriptor set is specified by
slink:VkWriteDescriptorSet::pname:descriptorType, which must: be one of the
values:

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

If pname:descriptorType is ename:VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER,
ename:VK_DESCRIPTOR_TYPE_STORAGE_BUFFER,
ename:VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER_DYNAMIC, or
ename:VK_DESCRIPTOR_TYPE_STORAGE_BUFFER_DYNAMIC, the elements of the
slink:VkWriteDescriptorSet::pname:pBufferInfo array of
slink:VkDescriptorBufferInfo structures will be used to update the
descriptors, and other arrays will be ignored.

If pname:descriptorType is ename:VK_DESCRIPTOR_TYPE_UNIFORM_TEXEL_BUFFER or
ename:VK_DESCRIPTOR_TYPE_STORAGE_TEXEL_BUFFER, the
slink:VkWriteDescriptorSet::pname:pTexelBufferView array will be used to
update the descriptors, and other arrays will be ignored.

If pname:descriptorType is ename:VK_DESCRIPTOR_TYPE_SAMPLER,
ename:VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER,
ename:VK_DESCRIPTOR_TYPE_SAMPLED_IMAGE,
ename:VK_DESCRIPTOR_TYPE_STORAGE_IMAGE, or
ename:VK_DESCRIPTOR_TYPE_INPUT_ATTACHMENT, the elements of the
slink:VkWriteDescriptorSet::pname:pImageInfo array of
slink:VkDescriptorImageInfo structures will be used to update the
descriptors, and other arrays will be ignored.

// refEnd VkDescriptorType

// refBegin VkDescriptorBufferInfo Structure specifying descriptor buffer info

The sname:VkDescriptorBufferInfo structure is defined as:

include::../api/structs/VkDescriptorBufferInfo.txt[]

  * pname:buffer is the buffer resource.
  * pname:offset is the offset in bytes from the start of pname:buffer.
    Access to buffer memory via this descriptor uses addressing that is
    relative to this starting offset.
  * pname:range is the size in bytes that is used for this descriptor
    update, or ename:VK_WHOLE_SIZE to use the range from pname:offset to the
    end of the buffer.
+
--
[NOTE]
.Note
====
When using ename:VK_WHOLE_SIZE, the effective range must: not be larger than
the maximum range for the descriptor type
(<<features-limits-maxUniformBufferRange, maxUniformBufferRange>> or
<<features-limits-maxStorageBufferRange, maxStorageBufferRange>>).
This means that ename:VK_WHOLE_SIZE is not typically useful in the common
case where uniform buffer descriptors are suballocated from a buffer that is
much larger than pname:maxUniformBufferRange.
====
--
+
For ename:VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER_DYNAMIC and
ename:VK_DESCRIPTOR_TYPE_STORAGE_BUFFER_DYNAMIC descriptor types,
pname:offset is the base offset from which the dynamic offset is applied and
pname:range is the static size used for all dynamic offsets.

include::../validity/structs/VkDescriptorBufferInfo.txt[]

// refBegin VkDescriptorImageInfo Structure specifying descriptor image info

The sname:VkDescriptorImageInfo structure is defined as:

include::../api/structs/VkDescriptorImageInfo.txt[]

  * pname:sampler is a sampler handle, and is used in descriptor updates for
    types ename:VK_DESCRIPTOR_TYPE_SAMPLER and
    ename:VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER if the binding being
    updated does not use immutable samplers.
  * pname:imageView is an image view handle, and is used in descriptor
    updates for types ename:VK_DESCRIPTOR_TYPE_SAMPLED_IMAGE,
    ename:VK_DESCRIPTOR_TYPE_STORAGE_IMAGE,
    ename:VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER, and
    ename:VK_DESCRIPTOR_TYPE_INPUT_ATTACHMENT.
  * pname:imageLayout is the layout that the image will be in at the time
    this descriptor is accessed.
    pname:imageLayout is used in descriptor updates for types
    ename:VK_DESCRIPTOR_TYPE_SAMPLED_IMAGE,
    ename:VK_DESCRIPTOR_TYPE_STORAGE_IMAGE,
    ename:VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER, and
    ename:VK_DESCRIPTOR_TYPE_INPUT_ATTACHMENT.

Members of sname:VkDescriptorImageInfo that are not used in an update (as
described above) are ignored.

include::../validity/structs/VkDescriptorImageInfo.txt[]

// refBegin VkCopyDescriptorSet Structure specifying a copy descriptor set operation

The sname:VkCopyDescriptorSet structure is defined as:

include::../api/structs/VkCopyDescriptorSet.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to an extension-specific structure.
  * pname:srcSet, pname:srcBinding, and pname:srcArrayElement are the source
    set, binding, and array element, respectively.
  * pname:dstSet, pname:dstBinding, and pname:dstArrayElement are the
    destination set, binding, and array element, respectively.
  * pname:descriptorCount is the number of descriptors to copy from the
    source to destination.
    If pname:descriptorCount is greater than the number of remaining array
    elements in the source or destination binding, those affect consecutive
    bindings in a manner similar to slink:VkWriteDescriptorSet above.

include::../validity/structs/VkCopyDescriptorSet.txt[]


[[descriptorsets-binding]]
=== Descriptor Set Binding

// refBegin vkCmdBindDescriptorSets Binds descriptor sets to a command buffer

To bind one or more descriptor sets to a command buffer, call:

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

  * pname:commandBuffer is the command buffer that the descriptor sets will
    be bound to.
  * pname:pipelineBindPoint is a elink:VkPipelineBindPoint indicating
    whether the descriptors will be used by graphics pipelines or compute
    pipelines.
    There is a separate set of bind points for each of graphics and compute,
    so binding one does not disturb the other.
  * pname:layout is a sname:VkPipelineLayout object used to program the
    bindings.
  * pname:firstSet is the set number of the first descriptor set to be
    bound.
  * pname:descriptorSetCount is the number of elements in the
    pname:pDescriptorSets array.
  * pname:pDescriptorSets is an array of handles to sname:VkDescriptorSet
    objects describing the descriptor sets to write to.
  * pname:dynamicOffsetCount is the number of dynamic offsets in the
    pname:pDynamicOffsets array.
  * pname:pDynamicOffsets is a pointer to an array of code:uint32_t
    values specifying dynamic offsets.

fname:vkCmdBindDescriptorSets causes the sets numbered [pname:firstSet..
pname:firstSet+pname:descriptorSetCount-1] to use the bindings stored in
pname:pDescriptorSets[0..pname:descriptorSetCount-1] for subsequent
rendering commands (either compute or graphics, according to the
pname:pipelineBindPoint).
Any bindings that were previously applied via these sets are no longer
valid.

Once bound, a descriptor set affects rendering of subsequent graphics or
compute commands in the command buffer until a different set is bound to the
same set number, or else until the set is disturbed as described in
<<descriptorsets-compatibility, Pipeline Layout Compatibility>>.

A compatible descriptor set must: be bound for all set numbers that any
shaders in a pipeline access, at the time that a draw or dispatch command is
recorded to execute using that pipeline.
However, if none of the shaders in a pipeline statically use any bindings
with a particular set number, then no descriptor set need be bound for that
set number, even if the pipeline layout includes a non-trivial descriptor
set layout for that set number.

If any of the sets being bound include dynamic uniform or storage buffers,
then pname:pDynamicOffsets includes one element for each array element in
each dynamic descriptor type binding in each set.
Values are taken from pname:pDynamicOffsets in an order such that all
entries for set N come before set N+1; within a set, entries are ordered by
the binding numbers in the descriptor set layouts; and within a binding
array, elements are in order.
pname:dynamicOffsetCount must: equal the total number of dynamic descriptors
in the sets being bound.

The effective offset used for dynamic uniform and storage buffer bindings is
the sum of the relative offset taken from pname:pDynamicOffsets, and the
base address of the buffer plus base offset in the descriptor set.
The length of the dynamic uniform and storage buffer bindings is the buffer
range as specified in the descriptor set.

Each of the pname:pDescriptorSets must: be compatible with the pipeline
layout specified by pname:layout.
The layout used to program the bindings must: also be compatible with the
pipeline used in subsequent graphics or compute commands, as defined in the
<<descriptorsets-compatibility, Pipeline Layout Compatibility>> section.

The descriptor set contents bound by a call to fname:vkCmdBindDescriptorSets
may: be consumed during host execution of the command, or during shader
execution of the resulting draws, or any time in between.
Thus, the contents must: not be altered (overwritten by an update command,
or freed) between when the command is recorded and when the command
completes executing on the queue.
The contents of pname:pDynamicOffsets are consumed immediately during
execution of fname:vkCmdBindDescriptorSets.
Once all pending uses have completed, it is legal to update and reuse a
descriptor set.

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


=== Push Constant Updates

[[descriptorsets-push-constants]]

As described above in section <<descriptorsets-pipelinelayout, Pipeline
Layouts>>, the pipeline layout defines shader push constants which are
updated via Vulkan commands rather than via writes to memory or copy
commands.

[NOTE]
.Note
====
Push constants represent a high speed path to modify constant data in
pipelines that is expected to outperform memory-backed resource updates.
====

The values of push constants are undefined at the start of a command buffer.

// refBegin vkCmdPushConstants Update the values of push constants

To update push constants, call:

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

  * pname:commandBuffer is the command buffer in which the push constant
    update will be recorded.
  * pname:layout is the pipeline layout used to program the push constant
    updates.
  * pname:stageFlags is a bitmask of elink:VkShaderStageFlagBits specifying
    the shader stages that will use the push constants in the updated range.
  * pname:offset is the start offset of the push constant range to update,
    in units of bytes.
  * pname:size is the size of the push constant range to update, in units of
    bytes.
  * pname:pValues is an array of pname:size bytes containing the new push
    constant values.

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