Vulkan-Docs/doc/specs/vulkan/appendices/VK_KHR_shared_presentable_i...

// Copyright (c) 2014-2017 The Khronos Group Inc.
// Copyright notice at https://www.khronos.org/registry/speccopyright.html

[[VK_KHR_shared_presentable_image]]
== VK_KHR_shared_presentable_image

*Name String*::
    +VK_KHR_shared_presentable_image+
*Extension Type*::
    Device extension
*Registered Extension Number*::
    112
*Last Modified Date*::
    2017-03-20
*Revision*::
    1
*IP Status*::
    No known IP claims.
*Dependencies*::
  - This extension is written against version 1.0 of the Vulkan API.
  - This extension requires +VK_KHR_swapchain+.
  - This extension requires +VK_KHR_surface+.
  - This extension requires +VK_KHR_get_physical_device_properties2+.
  - This extension requires +VK_KHR_get_surface_capabilities2+.
*Contributors*::
  - Alon Or-bach, Samsung Electronics
  - Ian Elliott, Google
  - Jesse Hall, Google
  - Pablo Ceballos, Google
  - Chris Forbes, Google
  - Jeff Juliano, NVIDIA
  - James Jones, NVIDIA
  - Daniel Rakos, AMD
  - Tobias Hector, Imagination Technologies
  - Graham Connor, Imagination Technologies
  - Michael Worcester, Imagination Technologies
  - Cass Everitt, Oculus
  - Johannes Van Waveren, Oculus
*Contacts*::
  - Alon Or-bach, Samsung Electronics

This extension extends +VK_KHR_swapchain+ to enable creation of a shared
presentable image.
This allows the application to use the image while the presention engine is
accessing it, in order to reduce the latency between rendering and
presentation.

=== New Object Types

None.

=== New Enum Constants

  * Extending ename:VkPresentModeKHR:
  ** ename:VK_PRESENT_MODE_SHARED_DEMAND_REFRESH_KHR
  ** ename:VK_PRESENT_MODE_SHARED_CONTINUOUS_REFRESH_KHR

  * Extending ename:VkImageLayout:
  ** ename:VK_IMAGE_LAYOUT_SHARED_PRESENT_KHR

  * Extending ename:VkStructureType:
  ** ename:VK_STRUCTURE_TYPE_SHARED_PRESENT_SURFACE_CAPABILITIES_KHR


=== New Enums

None.

=== New Structures

  * slink:VkSharedPresentSurfaceCapabilitiesKHR

=== New Functions

  * flink:vkGetSwapchainStatusKHR


=== Issues

1) Should we allow a Vulkan WSI swapchain to toggle between normal usage and
shared presentation usage?

*RESOLVED*: No.
WSI swapchains are typically recreated with new properties instead of having
their properties changed.
This can also save resources, assuming that fewer images are needed for
shared presentation, and assuming that most VR applications do not need to
switch between normal and shared usage.

2) Should we have a query for determining how the presentation engine
refresh is triggered?

*RESOLVED*: Yes.
This is done via which presentation modes a surface supports.

3) Should the object representing a shared presentable image be an extension
of a VkSwapchainKHR or a separate object?

*RESOLVED*: Extension of a swapchain due to overlap in creation properties
and to allow common functionality between shared and normal presentable
images and swapchains.

4) What should we call the extension and the new structures it creates?

*RESOLVED*: Shared presentable image / shared present.

5) Should the minImageCount and presentMode values of the
VkSwapchainCreateInfoKHR be ignored, or required to be compatible values?

*RESOLVED*: minImageCount must be set to 1, and presentMode should be set to
either VK_PRESENT_MODE_SHARED_DEMAND_REFRESH_KHR or
VK_PRESENT_MODE_SHARED_CONTINUOUS_REFRESH_KHR.

6) What should the layout of the shared presentable image be?

*RESOLVED*: After acquiring the shared presentable image, the application
must transition it to the VK_IMAGE_LAYOUT_SHARED_PRESENT_KHR layout prior to
it being used.
After this intial transition, any image usage that was requested during
swapchain creation can: be performed on the image without layout transitions
being performed.

7) Do we need a new API for the trigger to refresh new content?

*RESOLVED*: vkQueuePresentKHR to act as API to trigger a refresh, as will
allow combination with other compatible extensions to vkQueuePresentKHR.

8) How should an application detect a VK_ERROR_OUT_OF_DATE_KHR error on a
swapchain using the VK_PRESENT_MODE_SHARED_CONTINUOUS_REFRESH_KHR present
mode?

*RESOLVED*: Introduce vkGetSwapchainStatusKHR to allow applications to query
the status of a swapchain using a shared presentation mode.

9) What should subsequent calls to vkQueuePresentKHR for CONTINUOUS_REFRESH
swapchains be defined to do?

*RESOLVED*: State that implementations may use it as a hint for updated
content.

10) Can the ownership of a shared presentable image be transferred to a
different queue?

*RESOLVED*: No.
It is not possible to transfer ownership of a shared presentable image
obtained from a swapchain created using VK_SHARING_MODE_EXCLUSIVE after it
has been presented.

11) How should vkQueueSubmit behave if a command buffer uses an image from
an OUT_OF_DATE swapchain?

*RESOLVED*: vkQueueSubmit is expected to return the VK_ERROR_DEVICE_LOST
error.

12) Can Vulkan provide any guarantee on the order of rendering, to enable
beam chasing?

*RESOLVED*: This could be achieved via use of render passes to ensure strip
rendering.


=== Version History
 * Revision 1, 2017-03-20 (Alon Or-bach)
   - Internal revisions
Change log for May 12, 2017 Vulkan 1.0.49 spec update: * Bump API patch number and header version number to 49 for this update. Github Issues: * Modify reference page extraction script to make internal links to spec anchors refer to the core specification instead of being dangling links (public issue 455). * Fix GL_KHR_vulkan_glsl typo and add a nor-normative mapping to the newly published StorageBuffer class (public issue 466). * Both flink:vkEnumerateInstanceExtensionProperties and flink:vkEnumerateDeviceExtensionProperties return ename:VK_ERROR_LAYER_NOT_PRESENT, which covers the error case of an application providing a layer name that wasn't returned by ftext:vkEnumerate{Instance\|Device}LayerProperties (public issue 487). * The specification for flink:VkApplicationInfo::apiVersion says that the driver must return ename:VK_ERROR_INCOMPATIBLE_DRIVER in the case that pname:apiVersion specifies a non-supported version. That means that the valid usage should not also state that, and so the VU statement is removed. The VU had language about "`an effective substitute`" that would have been lost, and so it was moved to the pname:apiVersion description (public issue 488). Internal Issues: * Modify implicit validity generator script to assign asciidoc anchors to all valid usage statements it generates, and reflow.py script to insert Valid Usage ID (VUID) tags into the specification source files for explicit valid usage statements. This has no semantic effects on the specification, but will support the validation layer's detection of valid usage violations and allow it to link into the corresponding part of the specification (internal issue 583). * Assign VUID tags to all explicit VU statements and document the process and tag format in the style guide (internal issue 583). * Clarify the rules of whether to structure new functionality as instance extensions, device extensions, or both in the <<extended-functionality-instance-extensions-and-devices, Instance Extensions and Device Extensions>> section (internal issue 749). * Require that SPIR-V run-time arrays are only used with the code:BufferBlock decoration (internal issue 750). * Fix implicit and explicit valid usage statements for slink:VkWriteDescriptorSet::pname:dstSet (internal issue 767) * Fix SPIR-V code sample for ename:VK_DESCRIPTOR_TYPE_UNIFORM_TEXEL_BUFFER in the <<descriptorsets-uniformtexelbuffer, Uniform Texel Buffer>> section (internal issue 770). * Clarify that disabling depth testing also disables depth writes in the <<fragops-ds-state, Depth and Stencil Operations>> section (internal issue 775). * flink:VkDescriptorImageInfo::pname:imageLayout must match the actual imageLayout at the time the image is accessed. This was in the spec text, but needed an associated valid usage statement. * Note that only 32-bit atomic operations are supported in the <<spirvenv-module-validation, Validation Rules within a Module>> section. * Note that code:UniformConstant variables must not have initializers in the <<spirvenv-module-validation, Validation Rules within a Module>> section. * Add a new elink:VkObjectType enumeration to the core API, promoted from elink:VkDebugObjectTypeEXT, since it is used for much more than just the debug_report extension. New Extensions: * `VK_KHR_get_surface_capabilities2` * `VK_KHR_shared_presentable_image` 2017-05-12 08:37:16 +00:00			`// Copyright (c) 2014-2017 The Khronos Group Inc.`
			`// Copyright notice at https://www.khronos.org/registry/speccopyright.html`

			`[[VK_KHR_shared_presentable_image]]`
			`== VK_KHR_shared_presentable_image`

			`Name String::`
			`+VK_KHR_shared_presentable_image+`
			`Extension Type::`
			`Device extension`
			`Registered Extension Number::`
			`112`
			`Last Modified Date::`
			`2017-03-20`
			`Revision::`
			`1`
			`IP Status::`
			`No known IP claims.`
			`Dependencies::`
			`- This extension is written against version 1.0 of the Vulkan API.`
			`- This extension requires +VK_KHR_swapchain+.`
			`- This extension requires +VK_KHR_surface+.`
			`- This extension requires +VK_KHR_get_physical_device_properties2+.`
			`- This extension requires +VK_KHR_get_surface_capabilities2+.`
			`Contributors::`
			`- Alon Or-bach, Samsung Electronics`
			`- Ian Elliott, Google`
			`- Jesse Hall, Google`
			`- Pablo Ceballos, Google`
			`- Chris Forbes, Google`
			`- Jeff Juliano, NVIDIA`
			`- James Jones, NVIDIA`
			`- Daniel Rakos, AMD`
			`- Tobias Hector, Imagination Technologies`
			`- Graham Connor, Imagination Technologies`
			`- Michael Worcester, Imagination Technologies`
			`- Cass Everitt, Oculus`
			`- Johannes Van Waveren, Oculus`
			`Contacts::`
			`- Alon Or-bach, Samsung Electronics`

			`This extension extends +VK_KHR_swapchain+ to enable creation of a shared`
			`presentable image.`
			`This allows the application to use the image while the presention engine is`
			`accessing it, in order to reduce the latency between rendering and`
			`presentation.`

			`=== New Object Types`

			`None.`

			`=== New Enum Constants`

			`* Extending ename:VkPresentModeKHR:`
			`** ename:VK_PRESENT_MODE_SHARED_DEMAND_REFRESH_KHR`
			`** ename:VK_PRESENT_MODE_SHARED_CONTINUOUS_REFRESH_KHR`

			`* Extending ename:VkImageLayout:`
			`** ename:VK_IMAGE_LAYOUT_SHARED_PRESENT_KHR`

			`* Extending ename:VkStructureType:`
			`** ename:VK_STRUCTURE_TYPE_SHARED_PRESENT_SURFACE_CAPABILITIES_KHR`


			`=== New Enums`

			`None.`

			`=== New Structures`

			`* slink:VkSharedPresentSurfaceCapabilitiesKHR`

			`=== New Functions`

			`* flink:vkGetSwapchainStatusKHR`


			`=== Issues`

			`1) Should we allow a Vulkan WSI swapchain to toggle between normal usage and`
			`shared presentation usage?`

			`RESOLVED: No.`
			`WSI swapchains are typically recreated with new properties instead of having`
			`their properties changed.`
			`This can also save resources, assuming that fewer images are needed for`
			`shared presentation, and assuming that most VR applications do not need to`
			`switch between normal and shared usage.`

			`2) Should we have a query for determining how the presentation engine`
			`refresh is triggered?`

			`RESOLVED: Yes.`
			`This is done via which presentation modes a surface supports.`

			`3) Should the object representing a shared presentable image be an extension`
			`of a VkSwapchainKHR or a separate object?`

			`RESOLVED: Extension of a swapchain due to overlap in creation properties`
			`and to allow common functionality between shared and normal presentable`
			`images and swapchains.`

			`4) What should we call the extension and the new structures it creates?`

			`RESOLVED: Shared presentable image / shared present.`

			`5) Should the minImageCount and presentMode values of the`
			`VkSwapchainCreateInfoKHR be ignored, or required to be compatible values?`

			`RESOLVED: minImageCount must be set to 1, and presentMode should be set to`
			`either VK_PRESENT_MODE_SHARED_DEMAND_REFRESH_KHR or`
			`VK_PRESENT_MODE_SHARED_CONTINUOUS_REFRESH_KHR.`

			`6) What should the layout of the shared presentable image be?`

			`RESOLVED: After acquiring the shared presentable image, the application`
			`must transition it to the VK_IMAGE_LAYOUT_SHARED_PRESENT_KHR layout prior to`
			`it being used.`
			`After this intial transition, any image usage that was requested during`
			`swapchain creation can: be performed on the image without layout transitions`
			`being performed.`

			`7) Do we need a new API for the trigger to refresh new content?`

			`RESOLVED: vkQueuePresentKHR to act as API to trigger a refresh, as will`
			`allow combination with other compatible extensions to vkQueuePresentKHR.`

			`8) How should an application detect a VK_ERROR_OUT_OF_DATE_KHR error on a`
			`swapchain using the VK_PRESENT_MODE_SHARED_CONTINUOUS_REFRESH_KHR present`
			`mode?`

			`RESOLVED: Introduce vkGetSwapchainStatusKHR to allow applications to query`
			`the status of a swapchain using a shared presentation mode.`

			`9) What should subsequent calls to vkQueuePresentKHR for CONTINUOUS_REFRESH`
			`swapchains be defined to do?`

			`RESOLVED: State that implementations may use it as a hint for updated`
			`content.`

			`10) Can the ownership of a shared presentable image be transferred to a`
			`different queue?`

			`RESOLVED: No.`
			`It is not possible to transfer ownership of a shared presentable image`
			`obtained from a swapchain created using VK_SHARING_MODE_EXCLUSIVE after it`
			`has been presented.`

			`11) How should vkQueueSubmit behave if a command buffer uses an image from`
			`an OUT_OF_DATE swapchain?`

			`RESOLVED: vkQueueSubmit is expected to return the VK_ERROR_DEVICE_LOST`
			`error.`

			`12) Can Vulkan provide any guarantee on the order of rendering, to enable`
			`beam chasing?`

			`RESOLVED: This could be achieved via use of render passes to ensure strip`
			`rendering.`


			`=== Version History`
			`* Revision 1, 2017-03-20 (Alon Or-bach)`
			`- Internal revisions`