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Extension and Version Dependencies

• Requires support for Vulkan 1.0

• Requires VK_KHR_maintenance3 to be enabled for any device-level functionality

Extension Proposal

2022-08-22

IP Status

No known IP claims.

Contributors
• Joshua Ashton, Valve

• Hans-Kristian Arntzen, Valve

Description

This extension allows applications to reduce descriptor memory footprint by allowing a descriptor to be able to mutate to a given list of descriptor types depending on which descriptor types are written into, or copied into a descriptor set.

The main use case this extension intends to address is descriptor indexing with VK_DESCRIPTOR_BINDING_VARIABLE_DESCRIPTOR_COUNT_BIT where the descriptor types are completely generic, as this means applications can allocate one large descriptor set, rather than having one large descriptor set per descriptor type, which significantly bloats descriptor memory usage and causes performance issues.

This extension also adds a mechanism to declare that a descriptor pool, and therefore the descriptor sets that are allocated from it, reside only in host memory; as such these descriptors can only be updated/copied, but not bound.

These features together allow much more efficient emulation of the raw D3D12 binding model. This extension is primarily intended to be useful for API layering efforts.

New Enum Constants

• VK_EXT_MUTABLE_DESCRIPTOR_TYPE_EXTENSION_NAME

• VK_EXT_MUTABLE_DESCRIPTOR_TYPE_SPEC_VERSION

• Extending VkDescriptorPoolCreateFlagBits:

• VK_DESCRIPTOR_POOL_CREATE_HOST_ONLY_BIT_EXT

• Extending VkDescriptorSetLayoutCreateFlagBits:

• VK_DESCRIPTOR_SET_LAYOUT_CREATE_HOST_ONLY_POOL_BIT_EXT

• Extending VkDescriptorType:

• VK_DESCRIPTOR_TYPE_MUTABLE_EXT

• Extending VkStructureType:

• VK_STRUCTURE_TYPE_MUTABLE_DESCRIPTOR_TYPE_CREATE_INFO_EXT

• VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_MUTABLE_DESCRIPTOR_TYPE_FEATURES_EXT