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

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

[[pipelines]]
= Pipelines

The following <<pipelines-block-diagram,figure>> shows a block diagram of
the {apiname} pipelines. Some {apiname} commands specify geometric objects
to be drawn or computational work to be performed, while others specify
state controlling how objects are handled by the various pipeline stages, or
control data transfer between memory organized as images and buffers.
Commands are effectively sent through a processing pipeline, either a
_graphics pipeline_ or a _compute pipeline_.

The first stage of the <<pipelines-graphics,graphics pipeline>>
(<<drawing,Input Assembler>>) assembles vertices to form
geometric primitives such as points, lines, and triangles, based on a
requested primitive topology. In the next stage (<<shaders-vertex,Vertex
Shader>>) vertices can: be transformed, computing positions and attributes
for each vertex. If <<tessellation,tessellation>> and/or
<<geometry,geometry>> shaders are supported, they can: then generate
multiple primitives from a single input primitive, possibly changing the
primitive topology or generating additional attribute data in the process.

The final resulting primitives are <<vertexpostproc-clipping,clipped>> to a
clip volume in preparation for the next stage, <<primsrast,Rasterization>>.
The rasterizer produces a series of framebuffer addresses and values using a
two-dimensional description of a point, line segment, or triangle. Each
_fragment_ so produced is fed to the next stage (<<shaders-fragment,Fragment
Shader>>) that performs operations on individual fragments before they
finally alter the framebuffer. These operations include conditional updates
into the framebuffer based on incoming and previously stored depth values
(to effect <<fragops-depth,depth buffering>>),
<<framebuffer-blending,blending>> of incoming fragment colors with stored
colors, as well as <<framebuffer-blendoperations,masking>>,
<<fragops-stencil,stenciling>>, and other <<framebuffer-logicop,logical
operations>> on fragment values.

Framebuffer operations read and write the color and depth/stencil
attachments of the framebuffer for a given subpass of a
<<renderpass,render pass instance>>. The attachments can: be used as input
attachments in the fragment shader in a later subpass of the same render
pass.

The <<pipelines-compute,compute pipeline>> is a separate pipeline from the
graphics pipeline, which operates on one-, two-, or three-dimensional
workgroups which can: read from and write to buffer and image memory.

This ordering is meant only as a tool for describing {apiname}, not as a
strict rule of how {apiname} is implemented, and we present it only as a
means to organize the various operations of the pipelines.

[[pipelines-block-diagram]]
image::images/pipeline.{svgpdf}[title="Block diagram of the Vulkan pipeline",width="{svgpdf@pdf:500:800}",align="center"]

Each pipeline is controlled by a monolithic object created from a
description of all of the shader stages and any relevant fixed-function
stages. <<interfaces,Linking>> the whole pipeline together allows
the optimization of shaders based on their input/outputs and eliminates
expensive draw time state validation.

A pipeline object is bound to the device state in command buffers. Any
pipeline object state that is marked as dynamic is not applied to the device
state when the pipeline is bound. Dynamic state not set by binding the
pipeline object can: be modified at any time and persists for the lifetime
of the command buffer, or until modified by another dynamic state command or
another pipeline bind. No state, including dynamic state, is inherited from
one command buffer to another. Only dynamic state that is required: for the
operations performed in the command buffer needs to be set. For example, if
blending is disabled by the pipeline state then the dynamic color blend
constants do not need to be specified in the command buffer, even if this
state is marked as dynamic in the pipeline state object. If a new pipeline
object is bound with state not marked as dynamic after a previous pipeline
object with that same state as dynamic, the new pipeline object state will
override the dynamic state. Modifying dynamic state that is not set as
dynamic by the pipeline state object will lead to undefined results.


[[pipelines-compute]]
== Compute Pipelines

Compute pipelines consist of a single static compute shader stage and the
pipeline layout.

The compute pipeline encapsulates a compute shader and is created by calling
fname:vkCreateComputePipelines with pname:module and pname:pName selecting
an entry point from a shader module, where that entry point defines a valid
compute shader, in the sname:VkPipelineShaderStageCreateInfo structure
contained within the sname:VkComputePipelineCreateInfo structure.

Compute pipelines are created by calling:

include::../protos/vkCreateComputePipelines.txt[]

  * pname:device is the logical device that creates the compute pipelines.
  * pname:pipelineCache is either code:VK_NULL_HANDLE, indicating that
    pipeline caching is disabled; or the handle of a valid
    <<pipelines-cache,pipeline cache>> object, in which case use of that
    cache is enabled for the duration of the command.
  * pname:createInfoCount is the length of the pname:pCreateInfos and
    pname:Pipelines arrays.
  * pname:pCreateInfos is an array of sname:VkComputePipelineCreateInfo
    structures.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.
  * pname:pPipelines is a pointer to an array in which the resulting compute
    pipeline objects are returned.
+
--
ifdef::editing-notes[]
[NOTE]
.editing-note
====
TODO (Jon) - Should we say something like ``the i'th element of the
pname:pPipelines array is created based on the corresponding element of the
pname:pCreateInfos array''? Also for flink:vkCreateGraphicsPipelines below.
====
endif::editing-notes[]
--

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

The sname:VkComputePipelineCreateInfo structure is defined as:

include::../structs/VkComputePipelineCreateInfo.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to an extension-specific structure.
  * pname:flags provides options for pipeline creation, and is of type
    elink:VkPipelineCreateFlagBits.
  * pname:stage is a slink:VkPipelineShaderStageCreateInfo describing the
    compute shader.
  * pname:layout is the description of binding locations used by both the
    pipeline and descriptor sets used with the pipeline.
  * pname:basePipelineHandle is a pipeline to derive from
  * pname:basePipelineIndex is an index into the pname:pCreateInfos
    parameter to use as a pipeline to derive from

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

The parameters pname:basePipelineHandle and pname:basePipelineIndex are
described in more detail in
<<pipelines-pipeline-derivatives,Pipeline Derivatives>>.

pname:stage points to a structure of type
sname:VkPipelineShaderStageCreateInfo.

The sname:VkPipelineShaderStageCreateInfo structure is defined as:

include::../structs/VkPipelineShaderStageCreateInfo.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:stage is a elink:VkShaderStageFlagBits naming the pipeline stage.
  * pname:module is a sname:VkShaderModule object that contains the
    shader for this stage.
  * pname:pName is a pointer to a null-terminated UTF-8 string specifying
    the entry point name of the shader for this stage.
  * pname:pSpecializationInfo is a pointer to slink:VkSpecializationInfo, as
    described in <<pipelines-specialization-constants,Specialization
    Constants>>, and can: be `NULL`.

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

The elink:VkShaderStageFlagBits flags are defined as:

include::../enums/VkShaderStageFlagBits.txt[]


[[pipelines-graphics]]
== Graphics Pipelines

Graphics pipelines consist of multiple shader stages, multiple
fixed-function pipeline stages, and a pipeline layout, and are created by
calling fname:vkCreateGraphicsPipelines:

include::../protos/vkCreateGraphicsPipelines.txt[]

  * pname:device is the logical device that creates the graphics pipelines.
  * pname:pipelineCache is either code:VK_NULL_HANDLE, indicating that
    pipeline caching is disabled; or the handle of a valid
    <<pipelines-cache,pipeline cache>> object, in which case use of that
    cache is enabled for the duration of the command.
  * pname:createInfoCount is the length of the pname:pCreateInfos and
    pname:Pipelines arrays.
  * pname:pCreateInfos is an array of sname:VkGraphicsPipelineCreateInfo
    structures.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.
  * pname:pPipelines is a pointer to an array in which the resulting
    graphics pipeline objects are returned.

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

The sname:VkGraphicsPipelineCreateInfo structure includes an array of shader
create info structures containing all the desired active shader stages, as
well as creation info to define all relevant fixed-function stages, and a
pipeline layout.

The sname:VkGraphicsPipelineCreateInfo structure is defined as:

include::../structs/VkGraphicsPipelineCreateInfo.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to an extension-specific structure.
  * pname:flags is a bitfield of elink:VkPipelineCreateFlagBits controlling
    how the pipeline will be generated, as described below.
  * pname:stageCount is the number of entries in the pname:pStages array.
  * pname:pStages is an array of size pname:stageCount structures of type
    slink:VkPipelineShaderStageCreateInfo describing the set of the shader
    stages to be included in the graphics pipeline.
  * pname:pVertexInputState is a pointer to an instance of the
    slink:VkPipelineVertexInputStateCreateInfo structure.
  * pname:pInputAssemblyState is a pointer to an instance of the
    slink:VkPipelineInputAssemblyStateCreateInfo structure which determines
    input assembly behavior, as described in <<drawing, Drawing Commands>>.
  * pname:pTessellationState is a pointer to an instance of the
    slink:VkPipelineTessellationStateCreateInfo structure, or `NULL` if the
    pipeline does not include a tessellation control shader stage and
    tessellation evaluation shader stage.
  * pname:pViewportState is a pointer to an instance of the
    slink:VkPipelineViewportStateCreateInfo structure, or `NULL` if the
    pipeline has rasterization disabled.
  * pname:pRasterizationState is a pointer to an instance of the
    slink:VkPipelineRasterizationStateCreateInfo structure.
  * pname:pMultisampleState is a pointer to an instance of the
    slink:VkPipelineMultisampleStateCreateInfo, or `NULL` if the pipeline
    has rasterization disabled.
  * pname:pDepthStencilState is a pointer to an instance of the
    slink:VkPipelineDepthStencilStateCreateInfo structure, or `NULL` if the
    pipeline has rasterization disabled or if the subpass of the render pass
    the pipeline is created against does not use a depth/stencil attachment.
  * pname:pColorBlendState is a pointer to an instance of the
    slink:VkPipelineColorBlendStateCreateInfo structure, or `NULL` if the
    pipeline has rasterization disabled or if the subpass of the render pass
    the pipeline is created against does not use any color attachments.
  * pname:pDynamicState is a pointer to
    slink:VkPipelineDynamicStateCreateInfo and is used to indicate which
    properties of the pipeline state object are dynamic and can: be changed
    independently of the pipeline state. This can: be `NULL`, which means no
    state in the pipeline is considered dynamic.
  * pname:layout is the description of binding locations used by both the
    pipeline and descriptor sets used with the pipeline.
  * pname:renderPass is a handle to a render pass object describing the
    environment in which the pipeline will be used; the pipeline can: be
    used with an instance of any render pass compatible with the one
    provided. See <<renderpass-compatibility,Render Pass Compatibility>> for
    more information.
  * pname:subpass is the index of the subpass in pname:renderPass where this
    pipeline will be used.
  * pname:basePipelineHandle is a pipeline to derive from.
  * pname:basePipelineIndex is an index into the pname:pCreateInfos
    parameter to use as a pipeline to derive from.

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

The parameters pname:basePipelineHandle and pname:basePipelineIndex are
described in more detail in
<<pipelines-pipeline-derivatives,Pipeline Derivatives>>.

pname:pStages points to an array of slink:VkPipelineShaderStageCreateInfo
structures, which were previously described in
<<pipelines-compute,Compute Pipelines>>.

Bits which can: be set in pname:flags are:

include::../enums/VkPipelineCreateFlagBits.txt[]

  * ename:VK_PIPELINE_CREATE_DISABLE_OPTIMIZATION_BIT specifies that the
    created pipeline will not be optimized. Using this flag may: reduce
    the time taken to create the pipeline.
  * ename:VK_PIPELINE_CREATE_ALLOW_DERIVATIVES_BIT specifies that the
    pipeline to be created is allowed to be the parent of a pipeline that
    will be created in a subsequent call to flink:vkCreateGraphicsPipelines.
  * ename:VK_PIPELINE_CREATE_DERIVATIVE_BIT specifies that the pipeline to
    be created will be a child of a previously created parent pipeline.

It is valid to set both ename:VK_PIPELINE_CREATE_ALLOW_DERIVATIVES_BIT and
ename:VK_PIPELINE_CREATE_DERIVATIVE_BIT. This allows a pipeline to be both a
parent and possibly a child in a pipeline hierarchy. See
<<pipelines-pipeline-derivatives,Pipeline Derivatives>> for more
information.

pname:pDynamicState points to a structure of type
sname:VkPipelineDynamicStateCreateInfo.

The sname:VkPipelineDynamicStateCreateInfo structure is defined as:

include::../structs/VkPipelineDynamicStateCreateInfo.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:dynamicStateCount is the number of elements in the
    pname:pDynamicStates array.
  * pname:pDynamicStates is an array of elink:VkDynamicState enums which
    indicate which pieces of pipeline state will use the values from dynamic
    state commands rather than from the pipeline state creation info.

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

The elink:VkDynamicState enumerants are defined as:

include::../enums/VkDynamicState.txt[]

  * ename:VK_DYNAMIC_STATE_VIEWPORT indicates that the pname:pViewports
    state in sname:VkPipelineViewportStateCreateInfo will be ignored and
    must: be set dynamically with flink:vkCmdSetViewport before any draw
    commands. The number of viewports used by a pipeline is still
    specified by the pname:viewportCount member of
    sname:VkPipelineViewportStateCreateInfo.
  * ename:VK_DYNAMIC_STATE_SCISSOR indicates that the pname:pScissors
    state in sname:VkPipelineViewportStateCreateInfo will be ignored and
    must: be set dynamically with flink:vkCmdSetScissor before any draw
    commands. The number of scissor rectangles used by a pipeline is still
    specified by the pname:scissorCount member of
    sname:VkPipelineViewportStateCreateInfo.
  * ename:VK_DYNAMIC_STATE_LINE_WIDTH indicates that the pname:lineWidth
    state in sname:VkPipelineRasterizationStateCreateInfo will be ignored
    and must: be set dynamically with flink:vkCmdSetLineWidth before any
    draw commands that generate line primitives for the rasterizer.
  * ename:VK_DYNAMIC_STATE_DEPTH_BIAS indicates that the
    pname:depthBiasConstantFactor, pname:depthBiasClamp and
    pname:depthBiasSlopeFactor states in
    sname:VkPipelineRasterizationStateCreateInfo will be ignored and must:
    be set dynamically with flink:vkCmdSetDepthBias before any draws are
    performed with pname:depthBiasEnable in
    sname:VkPipelineRasterizationStateCreateInfo set to ename:VK_TRUE.
  * ename:VK_DYNAMIC_STATE_BLEND_CONSTANTS indicates that the
    pname:blendConstants state in
    sname:VkPipelineColorBlendStateCreateInfo will be ignored and must: be
    set dynamically with flink:vkCmdSetBlendConstants before any draws are
    performed with a pipeline state with
    sname:VkPipelineColorBlendAttachmentState member pname:blendEnable set
    to ename:VK_TRUE and any of the blend functions using a constant blend
    color.
  * ename:VK_DYNAMIC_STATE_DEPTH_BOUNDS indicates that the
    pname:minDepthBounds and pname:maxDepthBounds states of
    slink:VkPipelineDepthStencilStateCreateInfo will be ignored and must:
    be set dynamically with flink:vkCmdSetDepthBounds before any draws are
    performed with a pipeline state with
    sname:VkPipelineDepthStencilStateCreateInfo member
    pname:depthBoundsTestEnable set to ename:VK_TRUE.
  * ename:VK_DYNAMIC_STATE_STENCIL_COMPARE_MASK indicates that the
    pname:compareMask state in
    sname:VkPipelineDepthStencilStateCreateInfo for both pname:front and
    pname:back will be ignored and must: be set dynamically with
    flink:vkCmdSetStencilCompareMask before any draws are performed with a
    pipeline state with sname:VkPipelineDepthStencilStateCreateInfo member
    pname:stencilTestEnable set to ename:VK_TRUE
  * ename:VK_DYNAMIC_STATE_STENCIL_WRITE_MASK indicates that the
    pname:writeMask state in sname:VkPipelineDepthStencilStateCreateInfo
    for both pname:front and pname:back will be ignored and must: be set
    dynamically with flink:vkCmdSetStencilWriteMask before any draws are
    performed with a pipeline state with
    sname:VkPipelineDepthStencilStateCreateInfo member
    pname:stencilTestEnable set to ename:VK_TRUE
  * ename:VK_DYNAMIC_STATE_STENCIL_REFERENCE indicates that the
    pname:reference state in sname:VkPipelineDepthStencilStateCreateInfo
    for both pname:front and pname:back will be ignored and must: be set
    dynamically with flink:vkCmdSetStencilReference before any draws are
    performed with a pipeline state with
    sname:VkPipelineDepthStencilStateCreateInfo member
    pname:stencilTestEnable set to ename:VK_TRUE

If tessellation shader stages are omitted, the tessellation shading and
fixed-function stages of the pipeline are skipped.

If a geometry shader is omitted, the geometry shading stage is skipped.

If a fragment shader is omitted, the results of fragment processing are
undefined. Specifically, any fragment color outputs
are considered to have undefined values, and the fragment depth is
considered to be unmodified. This can: be useful for depth-only rendering.

Presence of a shader stage in a pipeline is indicated by including a valid
sname:VkPipelineShaderStageCreateInfo with pname:module and pname:pName
selecting an entry point from a shader module, where that entry point is
valid for the stage specified by pname:stage.

Presence of some of the fixed-function stages in the pipeline is implicitly
derived from enabled shaders and provided state. For example, the
fixed-function tessellator is always present when the pipeline has valid
Tessellation Control and Tessellation Evaluation shaders.

.For example:
  * Depth/stencil-only rendering in a subpass with no color attachments
  ** Active Pipeline Shader Stages
  *** Vertex Shader
  ** Required: Fixed-Function Pipeline Stages
  *** slink:VkPipelineVertexInputStateCreateInfo
  *** slink:VkPipelineInputAssemblyStateCreateInfo
  *** slink:VkPipelineViewportStateCreateInfo
  *** slink:VkPipelineRasterizationStateCreateInfo
  *** slink:VkPipelineMultisampleStateCreateInfo
  *** slink:VkPipelineDepthStencilStateCreateInfo
  * Color-only rendering in a subpass with no depth/stencil attachment
  ** Active Pipeline Shader Stages
  *** Vertex Shader
  *** Fragment Shader
  ** Required: Fixed-Function Pipeline Stages
  *** slink:VkPipelineVertexInputStateCreateInfo
  *** slink:VkPipelineInputAssemblyStateCreateInfo
  *** slink:VkPipelineViewportStateCreateInfo
  *** slink:VkPipelineRasterizationStateCreateInfo
  *** slink:VkPipelineMultisampleStateCreateInfo
  *** slink:VkPipelineColorBlendStateCreateInfo
  * Rendering pipeline with tessellation and geometry shaders
  ** Active Pipeline Shader Stages
  *** Vertex Shader
  *** Tessellation Control Shader
  *** Tessellation Evaluation Shader
  *** Geometry Shader
  *** Fragment Shader
  ** Required: Fixed-Function Pipeline Stages
  *** slink:VkPipelineVertexInputStateCreateInfo
  *** slink:VkPipelineInputAssemblyStateCreateInfo
  *** slink:VkPipelineTessellationStateCreateInfo
  *** slink:VkPipelineViewportStateCreateInfo
  *** slink:VkPipelineRasterizationStateCreateInfo
  *** slink:VkPipelineMultisampleStateCreateInfo
  *** slink:VkPipelineDepthStencilStateCreateInfo
  *** slink:VkPipelineColorBlendStateCreateInfo


[[pipelines-destruction]]
== Pipeline destruction

To destroy a graphics or compute pipeline, call:

include::../protos/vkDestroyPipeline.txt[]

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

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


[[pipelines-multiple]]
== Multiple Pipeline Creation

Multiple pipelines can: be created simultaneously by passing an array of
sname:VkGraphicsPipelineCreateInfo or sname:VkComputePipelineCreateInfo
structures into the flink:vkCreateGraphicsPipelines and
flink:vkCreateComputePipelines commands, respectively. Applications can:
group together similar pipelines to be created in a single call, and
implementations are encouraged to look for reuse opportunities within a
group-create.

When an application attempts to create many pipelines in a single command,
it is possible that some subset may: fail creation. In that case, the
corresponding entries in the pname:pPipelines output array will be filled
with code:VK_NULL_HANDLE values. If any pipeline fails creation (for
example, due to out of memory errors), the ftext:vkCreate*Pipelines commands
will return an error code. The implementation will attempt to create all
pipelines, and only return code:VK_NULL_HANDLE values for those that
actually failed.


[[pipelines-pipeline-derivatives]]
== Pipeline Derivatives

A pipeline derivative is a child pipeline created from a parent pipeline,
where the child and parent are expected to have much commonality. The goal
of derivative pipelines is that they be cheaper to create using the
parent as a starting point, and that it be more efficient (on either host or
device) to switch/bind between children of the same parent.

A derivative pipeline is created by setting the
ename:VK_PIPELINE_CREATE_DERIVATIVE_BIT flag in the
stext:Vk*PipelineCreateInfo structure. If this is set, then exactly one of
pname:basePipelineHandle or pname:basePipelineIndex members of the structure
must: have a valid handle/index, and indicates the parent pipeline. If
pname:basePipelineHandle is used, the parent pipeline must: have already
been created. If pname:basePipelineIndex is used, then the parent is being
created in the same command. code:VK_NULL_HANDLE acts as the invalid handle
for pname:basePipelineHandle, and -1 is the invalid index for
pname:basePipelineIndex. If pname:basePipelineIndex is used, the base
pipeline must: appear earlier in the array. The base pipeline must: have
been created with the ename:VK_PIPELINE_CREATE_ALLOW_DERIVATIVES_BIT flag
set.


[[pipelines-cache]]
== Pipeline Cache

Pipeline cache objects allow the result of pipeline construction to be
reused between pipelines and between runs of an application. Reuse between
pipelines is achieved by passing the same pipeline cache object when
creating multiple related pipelines. Reuse across runs of an application is
achieved by retrieving pipeline cache contents in one run of an application,
saving the contents, and using them to preinitialize a pipeline cache on a
subsequent run. The contents and size of the pipeline cache objects are
managed by the implementation. Applications can: control the amount of data
retrieved from a pipeline cache object.

Pipeline cache objects are created by calling:

include::../protos/vkCreatePipelineCache.txt[]

  * pname:device is the logical device that creates the pipeline cache
    object.
  * pname:pCreateInfo is a pointer to a sname:VkPipelineCacheCreateInfo
    structure that contains the initial parameters for the pipeline cache
    object.
  * pname:pAllocator controls host memory allocation as described in the
    <<memory-allocation, Memory Allocation>> chapter.
  * pname:pPipelineCache is a pointer to a sname:VkPipelineCache handle in
    which the resulting pipeline cache object is returned.

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

The sname:VkPipelineCacheCreateInfo structure is defined as:

include::../structs/VkPipelineCacheCreateInfo.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:initialDataSize is the number of bytes in pname:pInitialData. If
    pname:initialDataSize is zero, the pipeline cache will initially be
    empty.
  * pname:pInitialData is a pointer to previously retrieved pipeline
    cache data. If the pipeline cache data is incompatible (as defined
    below) with the device, the pipeline cache will be initially empty. If
    pname:initialDataSize is zero, pname:pInitialData is ignored.

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

Once created, a pipeline cache can: be passed to the
fname:vkCreateGraphicsPipelines and fname:vkCreateComputePipelines commands.
If the pipeline cache passed into these commands is not
code:VK_NULL_HANDLE, the implementation will query it for possible reuse
opportunities and update it with new content. The use of the pipeline cache
object in these commands is internally synchronized, and the same pipeline
cache object can: be used in multiple threads simultaneously.

[NOTE]
.Note
====
Implementations should: make every effort to limit any critical sections
to the actual accesses to the cache, which is expected to be significantly
shorter than the duration of the fname:vkCreateGraphicsPipelines and
fname:vkCreateComputePipelines commands.
====

Pipeline cache objects can: be merged using the command:

include::../protos/vkMergePipelineCaches.txt[]

  * pname:device is the logical device that owns the pipeline cache objects.
  * pname:dstCache is the handle of the pipeline cache to merge results
    into.
  * pname:srcCacheCount is the length of the pname:pSrcCaches array.
  * pname:pSrcCaches is an array of pipeline cache handles, which will be
    merged into pname:dstCache. The previous contents of pname:dstCache are
    included after the merge.

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

[NOTE]
.Note
====
The details of the merge operation are implementation dependent, but
implementations should: merge the contents of the specified pipelines and
prune duplicate entries.
====

Data can: be retrieved from a pipeline cache object using the command:

include::../protos/vkGetPipelineCacheData.txt[]

  * pname:device is the logical device that owns the pipeline cache.
  * pname:pipelineCache is the pipeline cache to retrieve data from.
  * pname:pDataSize is a pointer to a value related to the amount of data in
    the pipeline cache, as described below.
  * pname:pData is either `NULL` or a pointer to a buffer.

If pname:pData is `NULL`, then the maximum size of the data that can: be
retrieved from the pipeline cache, in bytes, is returned in pname:pDataSize.
Otherwise, pname:pDataSize must: point to a variable set by the user to the
size of the buffer, in bytes, pointed to by pname:pData, and on return the
variable is overwritten with the amount of data actually written to
pname:pData.

If pname:dataSize is less than the maximum size that can: be
retrieved by the pipeline cache, at most pname:pDataSize bytes will be
written to pname:pData, and fname:vkGetPipelineCacheData will return
ename:VK_INCOMPLETE. Any data written to pname:pData is valid and can: be
provided as the pname:pInitialData member of the
sname:VkPipelineCacheCreateInfo structure passed to
fname:vkCreatePipelineCache.

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

[[pipelines-cache-header]]
Applications can: store the data retrieved from the pipeline cache, and use
these data, possibly in a future run of the application, to populate new
pipeline cache objects. The results of pipeline compiles, however,
may: depend on the vendor ID, device ID, driver version, and other details
of the device. To enable applications to detect when previously retrieved
data is incompatible with the device, the initial bytes written to
pname:pData must: be a header consisting of the following members:

.Layout for pipeline cache header version VK_PIPELINE_CACHE_HEADER_VERSION_ONE
[width="85%",cols="8%,21%,71%",options="header"]
|=====
| Offset | Size | Meaning
| 0 | 4                    | length in bytes of the entire pipeline cache header
                             written as a stream of bytes, with the least
                             significant byte first
| 4 | 4                    | a elink:VkPipelineCacheHeaderVersion value
                             written as a stream of bytes, with the least
                             significant byte first
| 8 | 4                    | a vendor ID equal to
                             sname:VkPhysicalDeviceProperties::pname:vendorID
                             written as a stream of bytes, with the least
                             significant byte first
| 12 | 4                    | a device ID equal to
                             sname:VkPhysicalDeviceProperties::pname:deviceID
                             written as a stream of bytes, with the least
                             significant byte first
| 16 | ename:VK_UUID_SIZE   | a pipeline cache ID equal to
                             sname:VkPhysicalDeviceProperties::pname:pipelineCacheUUID
|=====

The first four bytes encode the length of the entire pipeline header, in
bytes. This value includes all fields in the header including the pipeline
cache version field and the size of the length field.

The next four bytes encode the pipeline cache version. This field is
interpreted as a elink:VkPipelineCacheHeaderVersion value, and must:
have one of the following values:

include::../enums/VkPipelineCacheHeaderVersion.txt[]

A consumer of the pipeline cache should use the cache version to interpret
the remainder of the cache header.

If pname:dataSize is less than what is necessary to store this
header, nothing will be written to pname:pData and zero will be written to
pname:dataSize.

To destroy a pipeline cache, call:

include::../protos/vkDestroyPipelineCache.txt[]

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

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


[[pipelines-specialization-constants]]
== Specialization Constants

Specialization constants are a mechanism whereby constants in a SPIR-V
module can: have their constant value specified at the time the
sname:VkPipeline is created. This allows a SPIR-V module to have constants
that can: be modified while executing an application that uses the Vulkan
API.

[NOTE]
.Note
====
Specialization constants are useful to allow a compute shader to have
its local workgroup size changed at runtime by the user, for example.
====

Each instance of the sname:VkPipelineShaderStageCreateInfo structure
contains a parameter pname:pSpecializationInfo, which can: be `NULL` to
indicate no specialization constants, or point to a
sname:VkSpecializationInfo structure.

The sname:VkSpecializationInfo structure is defined as:

include::../structs/VkSpecializationInfo.txt[]

  * pname:mapEntryCount is the number of entries in the pname:pMapEntries
    array.
  * pname:pMapEntries is a pointer to an array of
    sname:VkSpecializationMapEntry which maps constant IDs to offsets in
    pname:pData.
  * pname:dataSize is the byte size of the pname:pData buffer.
  * pname:pData contains the actual constant values to specialize with.

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

pname:pMapEntries points to a structure of type
sname:VkSpecializationMapEntry.

The sname:VkSpecializationMapEntry structure is defined as:

include::../structs/VkSpecializationMapEntry.txt[]

  * pname:constantID ID of the specialization constant in SPIR-V.
  * pname:offset byte offset of the specialization constant value within the
    supplied data buffer.
  * pname:size byte size of the specialization constant value within the
    supplied data buffer.

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

If a pname:constantID value is not a specialization constant ID used in the
shader, that map entry does not affect the behavior of the pipeline.

In human readable SPIR-V:

[source,glsl]
---------------------------------------------------
OpDecorate %x SpecId 13 ; decorate .x component of WorkgroupSize with ID 13
OpDecorate %y SpecId 42 ; decorate .y component of WorkgroupSize with ID 42
OpDecorate %z SpecId 3  ; decorate .z component of WorkgroupSize with ID 3
OpDecorate %wgsize BuiltIn WorkgroupSize ; decorate WorkgroupSize onto constant
%i32 = OpTypeInt 32 0 ; declare an unsigned 32-bit type
%uvec3 = OpTypeVector %i32 3 ; declare a 3 element vector type of unsigned 32-bit
%x = OpSpecConstant %i32 1 ; declare the .x component of WorkgroupSize
%y = OpSpecConstant %i32 1 ; declare the .y component of WorkgroupSize
%z = OpSpecConstant %i32 1 ; declare the .z component of WorkgroupSize
%wgsize = OpSpecConstantComposite %uvec3 %x %y %z ; declare WorkgroupSize
---------------------------------------------------

From the above we have three specialization constants, one for each of the
x, y & z elements of the WorkgroupSize vector.

Now to specialize the above via the specialization constants mechanism:

[source,{basebackend@docbook:c++:cpp}]
---------------------------------------------------
const VkSpecializationMapEntry entries[] =
{
    {
        13,                             // constantID
        0 * sizeof(uint32_t),           // offset
        sizeof(uint32_t)                // size
    },
    {
        42,                             // constantID
        1 * sizeof(uint32_t),           // offset
        sizeof(uint32_t)                // size
    },
    {
        3,                              // constantID
        2 * sizeof(uint32_t),           // offset
        sizeof(uint32_t)                // size
    }
};

const uint32_t data[] = { 16, 8, 4 }; // our workgroup size is 16x8x4

const VkSpecializationInfo info =
{
    3,                                  // mapEntryCount
    entries,                            // pMapEntries
    3 * sizeof(uint32_t),               // dataSize
    data,                               // pData
};
---------------------------------------------------

Then when calling fname:vkCreateComputePipelines, and passing the
sname:VkSpecializationInfo we defined as the pname:pSpecializationInfo
parameter of sname:VkPipelineShaderStageCreateInfo, we will create a compute
pipeline with the runtime specified local workgroup size.

Another example would be that an application has a SPIR-V module that has
some platform-dependent constants they wish to use.

In human readable SPIR-V:

// [source,{basebackend@docbook:c:glsl}]
[source,glsl]
---------------------------------------------------
OpDecorate %1 SpecId 0  ; decorate our signed 32-bit integer constant
OpDecorate %2 SpecId 12 ; decorate our 32-bit floating-point constant
%i32 = OpTypeInt 32 1   ; declare a signed 32-bit type
%float = OpTypeFloat 32 ; declare a 32-bit floating-point type
%1 = OpSpecConstant %i32 -1 ; some signed 32-bit integer constant
%2 = OpSpecConstant %float 0.5 ; some 32-bit floating-point constant
---------------------------------------------------

From the above we have two specialization constants, one is a signed 32-bit
integer and the second is a 32-bit floating-point.

Now to specialize the above via the specialization constants mechanism:

[source,{basebackend@docbook:c++:cpp}]
---------------------------------------------------
struct SpecializationData {
    int32_t data0;
    float data1;
};

const VkSpecializationMapEntry entries[] =
{
    {
        0,                                    // constantID
        offsetof(SpecializationData, data0),  // offset
        sizeof(SpecializationData::data0)     // size
    },
    {
        12,                                   // constantID
        offsetof(SpecializationData, data1),  // offset
        sizeof(SpecializationData::data1)     // size
    }
};

SpecializationData data;
data.data0 = -42;    // set the data for the 32-bit integer
data.data1 = 42.0f;  // set the data for the 32-bit floating-point

const VkSpecializationInfo info =
{
    2,                                  // mapEntryCount
    entries,                            // pMapEntries
    sizeof(data),                       // dataSize
    &data,                              // pData
};
---------------------------------------------------

It is legal for a SPIR-V module with specializations to be compiled into a
pipeline where no specialization info was provided. SPIR-V specialization
constants contain default values such that if a specialization is not
provided, the default value will be used. In the examples above, it would be
valid for an application to only specialize some of the specialization
constants within the SPIR-V module, and let the other constants use their
default values encoded within the OpSpecConstant declarations.


[[pipelines-binding]]
== Pipeline Binding

Once a pipeline has been created, it can: be bound to the command buffer
using the command:

include::../protos/vkCmdBindPipeline.txt[]

  * pname:commandBuffer is the command buffer that the pipeline will be
    bound to.
  * pname:pipelineBindPoint specifies the bind point, and must: have one of
    the values
+
--
include::../enums/VkPipelineBindPoint.txt[]

specifying whether pname:pipeline will be bound as a compute
(ename:VK_PIPELINE_BIND_POINT_COMPUTE) or graphics
(ename:VK_PIPELINE_BIND_POINT_GRAPHICS) pipeline. There are separate bind
points for each of graphics and compute, so binding one does not disturb the
other.
--
  * pname:pipeline is the pipeline to be bound.

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

Once bound, a pipeline binding affects subsequent graphics or compute
commands in the command buffer until a different pipeline is bound to the
bind point. The pipeline bound to ename:VK_PIPELINE_BIND_POINT_COMPUTE
controls the behavior of flink:vkCmdDispatch and
flink:vkCmdDispatchIndirect. The pipeline bound to
ename:VK_PIPELINE_BIND_POINT_GRAPHICS controls the behavior of
flink:vkCmdDraw, flink:vkCmdDrawIndexed, flink:vkCmdDrawIndirect, and
flink:vkCmdDrawIndexedIndirect. No other commands are affected by the
pipeline state.