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## Extension and Version Dependencies

• Requires support for Vulkan 1.0

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

• Requires VK_KHR_get_physical_device_properties2 to be enabled for any device-level functionality

• Requires VK_KHR_get_surface_capabilities2 to be enabled for any device-level functionality

## Contact

2017-03-20

IP Status

No known IP claims.

Contributors
• Alon Or-bach, Samsung Electronics

• 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

## Description

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 Enum Constants

• VK_KHR_SHARED_PRESENTABLE_IMAGE_EXTENSION_NAME

• VK_KHR_SHARED_PRESENTABLE_IMAGE_SPEC_VERSION

• Extending VkImageLayout:

• VK_IMAGE_LAYOUT_SHARED_PRESENT_KHR

• Extending VkPresentModeKHR:

• VK_PRESENT_MODE_SHARED_CONTINUOUS_REFRESH_KHR

• VK_PRESENT_MODE_SHARED_DEMAND_REFRESH_KHR

• Extending VkStructureType:

• VK_STRUCTURE_TYPE_SHARED_PRESENT_SURFACE_CAPABILITIES_KHR

## 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 initial 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 VK_PRESENT_MODE_SHARED_CONTINUOUS_REFRESH_KHR 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 a VK_ERROR_OUT_OF_DATE_KHR 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