// Copyright (c) 2015-2016 The Khronos Group Inc. // Copyright notice at https://www.khronos.org/registry/speccopyright.html [[pipelines]] = Pipelines The following <> shows a block diagram of the Vulkan pipelines. Some Vulkan 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 <> (<>) assembles vertices to form geometric primitives such as points, lines, and triangles, based on a requested primitive topology. In the next stage (<>) vertices can: be transformed, computing positions and attributes for each vertex. If <> and/or <> 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 <> to a clip volume in preparation for the next stage, <>. 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 (<>) 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 <>), <> of incoming fragment colors with stored colors, as well as <>, <>, and other <> on fragment values. Framebuffer operations read and write the color and depth/stencil attachments of the framebuffer for a given subpass of a <>. The attachments can: be used as input attachments in the fragment shader in a later subpass of the same render pass. The <> 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 Vulkan, not as a strict rule of how Vulkan 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. <> 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 <> 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:pPipelines arrays. * pname:pCreateInfos is an array of sname:VkComputePipelineCreateInfo structures. * pname:pAllocator controls host memory allocation as described in the <> 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 <>. 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 <>, 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 <> 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:pPipelines arrays. * pname:pCreateInfos is an array of sname:VkGraphicsPipelineCreateInfo structures. * pname:pAllocator controls host memory allocation as described in the <> 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 <>. * 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 <> 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 <>. pname:pStages points to an array of slink:VkPipelineShaderStageCreateInfo structures, which were previously described in <>. 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 <> 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 <> 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 of the pipeline cache objects are managed by the implementation. Applications can: manage the host memory consumed by a pipeline cache object and 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 <> chapter. * pname:pPipelineCache is a pointer to a sname:VkPipelineCache handle in which the resulting pipeline cache object is returned. [NOTE] .Note ==== Applications can: track and manage the total host memory size of a pipeline cache object using the pname:pAllocator. Applications can: limit the amount of data retrieved from a pipeline cache object in fname:vkGetPipeineCacheData. Implementations shouldnot: internally limit the total number of entries added to a pipeline cache object or the total host memory consumed. ==== 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 <> 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.