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## Extension and Version Dependencies

• Requires Vulkan 1.0

• Requires VK_KHR_get_physical_device_properties2

• Requires VK_KHR_maintenance1

2018-08-01

IP Status

No known IP claims.

Contributors
• Daniel Rakos, AMD

• Jeff Bolz, NVIDIA

• Slawomir Grajewski, Intel

• Neil Henning, Codeplay

### Description

This extension introduces the ability to back uniform blocks directly with descriptor sets by storing inline uniform data within descriptor pool storage. Compared to push constants this new construct allows uniform data to be reused across multiple disjoint sets of draw or dispatch commands and may enable uniform data to be accessed with less indirections compared to uniforms backed by buffer memory.

### New Enum Constants

• VK_EXT_INLINE_UNIFORM_BLOCK_EXTENSION_NAME

• VK_EXT_INLINE_UNIFORM_BLOCK_SPEC_VERSION

• Extending VkDescriptorType:

• VK_DESCRIPTOR_TYPE_INLINE_UNIFORM_BLOCK_EXT

• Extending VkStructureType:

• VK_STRUCTURE_TYPE_DESCRIPTOR_POOL_INLINE_UNIFORM_BLOCK_CREATE_INFO_EXT

• VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_INLINE_UNIFORM_BLOCK_FEATURES_EXT

• VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_INLINE_UNIFORM_BLOCK_PROPERTIES_EXT

• VK_STRUCTURE_TYPE_WRITE_DESCRIPTOR_SET_INLINE_UNIFORM_BLOCK_EXT

### Issues

1) Do we need a new storage class for inline uniform blocks vs uniform blocks?

RESOLVED: No. The Uniform storage class is used to allow the same syntax used for both uniform buffers and inline uniform blocks.

2) Is the descriptor array index and array size expressed in terms of bytes or dwords for inline uniform block descriptors?

RESOLVED: In bytes, but both must be a multiple of 4, similar to how push constant ranges are specified. The descriptorCount of VkDescriptorSetLayoutBinding thus provides the total number of bytes a particular binding with an inline uniform block descriptor type can hold, while the srcArrayElement, dstArrayElement, and descriptorCount members of VkWriteDescriptorSet, VkCopyDescriptorSet, and VkDescriptorUpdateTemplateEntry (where applicable) specify the byte offset and number of bytes to write/copy to the binding’s backing store. Additionally, the stride member of VkDescriptorUpdateTemplateEntry is ignored for inline uniform blocks and a default value of one is used, meaning that the data to update inline uniform block bindings with must be contiguous in memory.

3) What layout rules apply for uniform blocks corresponding to inline constants?

RESOLVED: They use the same layout rules as uniform buffers.

4) Do we need to add non-uniform indexing features/properties as introduced by VK_EXT_descriptor_indexing for inline uniform blocks?

RESOLVED: No, because inline uniform blocks are not allowed to be “arrayed”. A single binding with an inline uniform block descriptor type corresponds to a single uniform block instance and the array indices inside that binding refer to individual offsets within the uniform block (see issue #2). However, this extension does introduce new features/properties about the level of support for update-after-bind inline uniform blocks.

5) Is the descriptorBindingVariableDescriptorCount feature introduced by VK_EXT_descriptor_indexing supported for inline uniform blocks?

RESOLVED: Yes, as long as other inline uniform block specific limits are respected.

6) Do the robustness guarantees of robustBufferAccess apply to inline uniform block accesses?

RESOLVED: No, similarly to push constants, as they are not backed by buffer memory like uniform buffers.

### Version History

• Revision 1, 2018-08-01 (Daniel Rakos)

• Internal revisions