VK_KHR_maintenance2

Other Extension Metadata

Last Modified Date

2017-09-05

Contributors

• Michael Worcester, Imagination Technologies
• Stuart Smith, Imagination Technologies
• Jeff Bolz, NVIDIA
• Daniel Koch, NVIDIA
• Jan-Harald Fredriksen, ARM
• Daniel Rakos, AMD
• Neil Henning, Codeplay
• Piers Daniell, NVIDIA

Description

VK_KHR_maintenance2 adds a collection of minor features that were intentionally left out or overlooked from the original Vulkan 1.0 release.

The new features are as follows:

• Allow the application to specify which aspect of an input attachment might be read for a given subpass.
• Allow implementations to express the clipping behavior of points.
• Allow creating images with usage flags that may not be supported for the base image’s format, but are supported for image views of the image that have a different but compatible format.
• Allow creating uncompressed image views of compressed images.
• Allow the application to select between an upper-left and lower-left origin for the tessellation domain space.
• Adds two new image layouts for depth stencil images to allow either the depth or stencil aspect to be read-only while the other aspect is writable.

Input Attachment Specification

Input attachment specification allows an application to specify which aspect of a multi-aspect image (e.g. a depth/stencil format) will be accessed via a subpassLoad operation.

On some implementations there may be a performance penalty if the implementation does not know (at vkCreateRenderPass time) which aspect(s) of multi-aspect images can be accessed as input attachments.

Promotion to Vulkan 1.1

All functionality in this extension is included in core Vulkan 1.1, with the KHR suffix omitted. The original type, enum, and command names are still available as aliases of the core functionality.

New Structures

• VkInputAttachmentAspectReferenceKHR
• Extending VkImageViewCreateInfo:
  • VkImageViewUsageCreateInfoKHR
• Extending VkPhysicalDeviceProperties2:
  • VkPhysicalDevicePointClippingPropertiesKHR
• Extending VkPipelineTessellationStateCreateInfo:
  • VkPipelineTessellationDomainOriginStateCreateInfoKHR
• Extending VkRenderPassCreateInfo:
  • VkRenderPassInputAttachmentAspectCreateInfoKHR

New Enums

• VkPointClippingBehaviorKHR
• VkTessellationDomainOriginKHR

New Enum Constants

• VK_KHR_MAINTENANCE2_EXTENSION_NAME
• VK_KHR_MAINTENANCE2_SPEC_VERSION
• VK_KHR_MAINTENANCE_2_EXTENSION_NAME
• VK_KHR_MAINTENANCE_2_SPEC_VERSION
• Extending VkImageCreateFlagBits:
  • VK_IMAGE_CREATE_BLOCK_TEXEL_VIEW_COMPATIBLE_BIT_KHR
  • VK_IMAGE_CREATE_EXTENDED_USAGE_BIT_KHR
• Extending VkImageLayout:
  • VK_IMAGE_LAYOUT_DEPTH_ATTACHMENT_STENCIL_READ_ONLY_OPTIMAL_KHR
  • VK_IMAGE_LAYOUT_DEPTH_READ_ONLY_STENCIL_ATTACHMENT_OPTIMAL_KHR
• Extending VkPointClippingBehavior:
  • VK_POINT_CLIPPING_BEHAVIOR_ALL_CLIP_PLANES_KHR
  • VK_POINT_CLIPPING_BEHAVIOR_USER_CLIP_PLANES_ONLY_KHR
• Extending VkStructureType:
  • VK_STRUCTURE_TYPE_IMAGE_VIEW_USAGE_CREATE_INFO_KHR
  • VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_POINT_CLIPPING_PROPERTIES_KHR
  • VK_STRUCTURE_TYPE_PIPELINE_TESSELLATION_DOMAIN_ORIGIN_STATE_CREATE_INFO_KHR
  • VK_STRUCTURE_TYPE_RENDER_PASS_INPUT_ATTACHMENT_ASPECT_CREATE_INFO_KHR
• Extending VkTessellationDomainOrigin:
  • VK_TESSELLATION_DOMAIN_ORIGIN_LOWER_LEFT_KHR
  • VK_TESSELLATION_DOMAIN_ORIGIN_UPPER_LEFT_KHR

Input Attachment Specification Example

Consider the case where a render pass has two subpasses and two attachments.

Attachment 0 has the format VK_FORMAT_D24_UNORM_S8_UINT, attachment 1 has some color format.

Subpass 0 writes to attachment 0, subpass 1 reads only the depth information from attachment 0 (using inputAttachmentRead) and writes to attachment 1.

    VkInputAttachmentAspectReferenceKHR references[] = {
        {
            .subpass = 1,
            .inputAttachmentIndex = 0,
            .aspectMask = VK_IMAGE_ASPECT_DEPTH_BIT
        }
    };

    VkRenderPassInputAttachmentAspectCreateInfoKHR specifyAspects = {
        .sType = VK_STRUCTURE_TYPE_RENDER_PASS_INPUT_ATTACHMENT_ASPECT_CREATE_INFO_KHR,
        .pNext = NULL,
        .aspectReferenceCount = 1,
        .pAspectReferences = references
    };


    VkRenderPassCreateInfo createInfo = {
        ...
        .pNext = &specifyAspects,
        ...
    };

    vkCreateRenderPass(...);

Issues

1) What is the default tessellation domain origin?

RESOLVED: Vulkan 1.0 originally inadvertently documented a lower-left origin, but the conformance tests and all implementations implemented an upper-left origin. This extension adds a control to select between lower-left (for compatibility with OpenGL) and upper-left, and we retroactively fix unextended Vulkan to have a default of an upper-left origin.

Version History

• Revision 1, 2017-04-28