VK_EXT_inline_uniform_block(3) Manual Page

139

1

Not ratified

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 drawing or dispatching commands and may enable uniform data to be accessed with fewer indirections compared to uniforms backed by buffer memory.

Functionality in this extension is included in core Vulkan 1.3, with the EXT suffix omitted. The original type, enum and command names are still available as aliases of the core functionality.

Vulkan 1.3 adds additional functionality related to this extension in the form of the maxInlineUniformTotalSize limit.

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.

VkDescriptorPoolInlineUniformBlockCreateInfoEXT, VkPhysicalDeviceInlineUniformBlockFeaturesEXT, VkPhysicalDeviceInlineUniformBlockPropertiesEXT, VkWriteDescriptorSetInlineUniformBlockEXT

For more information, see the Vulkan Specification

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