VK_DESCRIPTOR_UPDATE_TEMPLATE_TYPE_PUSH_DESCRIPTORS_KHR specifies that the descriptor update template will be used for push descriptor updates only.

VK_DESCRIPTOR_SET_LAYOUT_CREATE_PUSH_DESCRIPTOR_BIT_KHR specifies that descriptor sets must not be allocated using this layout, and descriptors are instead pushed by vkCmdPushDescriptorSetKHR.

vkCmdPushDescriptorSetKHR - Pushes descriptor updates into a command buffer

Parameters

• commandBuffer is the command buffer that the descriptors will be recorded in.

• pipelineBindPoint is a VkPipelineBindPoint indicating whether the descriptors will be used by graphics pipelines or compute pipelines. There is a separate set of push descriptor bindings for each of graphics and compute, so binding one does not disturb the other.
• layout is a VkPipelineLayout object used to program the bindings.
• set is the set number of the descriptor set in the pipeline layout that will be updated.
• descriptorWriteCount is the number of elements in the pDescriptorWrites array.
• pDescriptorWrites is a pointer to an array of VkWriteDescriptorSet structures describing the descriptors to be updated.

Description

Push descriptors are a small bank of descriptors whose storage is internally managed by the command buffer rather than being written into a descriptor set and later bound to a command buffer. Push descriptors allow for incremental updates of descriptors without managing the lifetime of descriptor sets.

When a command buffer begins recording, all push descriptors have undefined contents. Push descriptors can be updated incrementally and cause shaders to use the updated descriptors for subsequent rendering commands (either compute or graphics, according to the pipelineBindPoint) until the descriptor is overwritten, or else until the set is disturbed as described in Pipeline Layout Compatibility. When the set is disturbed or push descriptors with a different descriptor set layout are set, all push descriptors become invalid.

Valid descriptors must be pushed for all bindings that any shaders in a pipeline access, at the time that a draw or dispatch command is recorded to execute using that pipeline. This includes immutable sampler descriptors, which must be pushed before they are accessed by a pipeline. However, if none of the shaders in a pipeline statically use certain bindings in the push descriptor set, then those descriptors need not be valid.

Push descriptors do not use dynamic offsets. Instead, the corresponding non-dynamic descriptor types can be used and the offset member of VkDescriptorBufferInfo can be changed each time the descriptor is written.

Each element of pDescriptorWrites is interpreted as in VkWriteDescriptorSet, except the dstSet member is ignored.

To push an immutable sampler, use a VkWriteDescriptorSet with dstBinding and dstArrayElement selecting the immutable sampler’s binding. If the descriptor type is VK_DESCRIPTOR_TYPE_SAMPLER, the pImageInfo parameter is ignored and the immutable sampler is taken from the push descriptor set layout in the pipeline layout. If the descriptor type is VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER, the sampler member of the pImageInfo parameter is ignored and the immutable sampler is taken from the push descriptor set layout in the pipeline layout.

Valid Usage

• pipelineBindPoint must be supported by the commandBuffer’s parent VkCommandPool’s queue family

• set must be less than VkPipelineLayoutCreateInfo::setLayoutCount provided when layout was created
• set must be the unique set number in the pipeline layout that uses a descriptor set layout that was created with VK_DESCRIPTOR_SET_LAYOUT_CREATE_PUSH_DESCRIPTOR_BIT_KHR

Valid Usage (Implicit)

• commandBuffer must be a valid VkCommandBuffer handle

• pipelineBindPoint must be a valid VkPipelineBindPoint value
• layout must be a valid VkPipelineLayout handle
• pDescriptorWrites must be a valid pointer to an array of descriptorWriteCount valid VkWriteDescriptorSet structures
• commandBuffer must be in the recording state
• The VkCommandPool that commandBuffer was allocated from must support graphics, or compute operations
• descriptorWriteCount must be greater than 0
• Both of commandBuffer, and layout must have been created, allocated, or retrieved from the same VkDevice

Host Synchronization

• Host access to commandBuffer must be externally synchronized

• Host access to the VkCommandPool that commandBuffer was allocated from must be externally synchronized

Command Properties

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See Also

VkCommandBuffer, VkPipelineBindPoint, VkPipelineLayout, VkWriteDescriptorSet

vkCmdPushDescriptorSetWithTemplateKHR - Pushes descriptor updates into a command buffer using a descriptor update template

Parameters

• commandBuffer is the command buffer that the descriptors will be recorded in.

• descriptorUpdateTemplate A descriptor update template which defines how to interpret the descriptor information in pData.
• layout is a VkPipelineLayout object used to program the bindings. It must be compatible with the layout used to create the descriptorUpdateTemplate handle.
• set is the set number of the descriptor set in the pipeline layout that will be updated. This must be the same number used to create the descriptorUpdateTemplate handle.
• pData Points to memory which contains the descriptors for the templated update.

Valid Usage

• The pipelineBindPoint specified during the creation of the descriptor update template must be supported by the commandBuffer’s parent VkCommandPool’s queue family

• pData must be a valid pointer to a memory that contains one or more valid instances of VkDescriptorImageInfo, VkDescriptorBufferInfo, or VkBufferView in a layout defined by descriptorUpdateTemplate when it was created with vkCreateDescriptorUpdateTemplateKHR

Valid Usage (Implicit)

• commandBuffer must be a valid VkCommandBuffer handle

• descriptorUpdateTemplate must be a valid VkDescriptorUpdateTemplate handle
• layout must be a valid VkPipelineLayout handle
• commandBuffer must be in the recording state
• The VkCommandPool that commandBuffer was allocated from must support graphics, or compute operations
• Each of commandBuffer, descriptorUpdateTemplate, and layout must have been created, allocated, or retrieved from the same VkDevice

Host Synchronization

• Host access to commandBuffer must be externally synchronized

• Host access to the VkCommandPool that commandBuffer was allocated from must be externally synchronized

Command Properties

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API example.

struct AppBufferView {
    VkBufferView bufferView;
    uint32_t     applicationRelatedInformation;
};

struct AppDataStructure
{
    VkDescriptorImageInfo  imageInfo;          // a single image info
    // ... some more application related data
};

const VkDescriptorUpdateTemplateEntry descriptorUpdateTemplateEntries[] =
{
    // binding to a single image descriptor
    {
        0,                                           // binding
        0,                                           // dstArrayElement
        1,                                           // descriptorCount
        VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER,   // descriptorType
        offsetof(AppDataStructure, imageInfo),       // offset
        0                                            // stride is not required if descriptorCount is 1.
    }

};

// create an descriptor update template for descriptor set updates
const VkDescriptorUpdateTemplateCreateInfo createInfo =
{
    VK_STRUCTURE_TYPE_DESCRIPTOR_UPDATE_TEMPLATE_CREATE_INFO,  // sType
    NULL,                                                          // pNext
    0,                                                             // flags
    1,                                                             // descriptorUpdateEntryCount
    descriptorUpdateTemplateEntries,                               // pDescriptorUpdateEntries
    VK_DESCRIPTOR_UPDATE_TEMPLATE_TYPE_PUSH_DESCRIPTORS_KHR,       // templateType
    0,                                                             // descriptorSetLayout, ignored by given templateType
    VK_PIPELINE_BIND_POINT_GRAPHICS,                               // pipelineBindPoint
    myPipelineLayout,                                              // pipelineLayout
    0,                                                             // set
};

VkDescriptorUpdateTemplate myDescriptorUpdateTemplate;
myResult = vkCreateDescriptorUpdateTemplate(
    myDevice,
    &createInfo,
    NULL,
    &myDescriptorUpdateTemplate);
}

AppDataStructure appData;
// fill appData here or cache it in your engine
vkCmdPushDescriptorSetWithTemplateKHR(myCmdBuffer, myDescriptorUpdateTemplate, myPipelineLayout, 0,&appData);

See Also

VkCommandBuffer, VkDescriptorUpdateTemplate, VkPipelineLayout

VkPhysicalDevicePushDescriptorPropertiesKHR - Structure describing push descriptor limits that can be supported by an implementation

Members

The members of the VkPhysicalDevicePushDescriptorPropertiesKHR structure describe the following implementation-dependent limits:

Description

• maxPushDescriptors is the maximum number of descriptors that can be used in a descriptor set created with VK_DESCRIPTOR_SET_LAYOUT_CREATE_PUSH_DESCRIPTOR_BIT_KHR set.

Valid Usage (Implicit)

• sType must be VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_PUSH_DESCRIPTOR_PROPERTIES_KHR

See Also

VkStructureType