VK_KHR_display_swapchain(3)

# VK_KHR_display_swapchain(3) Manual Page

## Name

VK_KHR_display_swapchain - device extension

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## Registered Extension Number

4

## Revision

10

## Extension and Version Dependencies

- Requires Vulkan 1.0

- Requires `VK_KHR_swapchain`

- Requires `VK_KHR_display`

### Other Extension Metadata

Last Modified Date

  2017-03-13

IP Status

  No known IP claims.

Contributors

  - James Jones, NVIDIA

  - Jeff Vigil, Qualcomm

  - Jesse Hall, Google

### Description

This extension provides an API to create a swapchain directly on a device’s display without any underlying window system.

### New Commands

- vkCreateSharedSwapchainsKHR

### New Structures

- Extending VkPresentInfoKHR:

  - VkDisplayPresentInfoKHR

### New Enum Constants

- `VK_KHR_DISPLAY_SWAPCHAIN_EXTENSION_NAME`

- `VK_KHR_DISPLAY_SWAPCHAIN_SPEC_VERSION`

- Extending VkResult:

  - `VK_ERROR_INCOMPATIBLE_DISPLAY_KHR`

- Extending VkStructureType:

  - `VK_STRUCTURE_TYPE_DISPLAY_PRESENT_INFO_KHR`

### Issues

1) Should swapchains sharing images each hold a reference to the images, or should it be up to the application to destroy the swapchains and images in an order that avoids the need for reference counting?

RESOLVED: Take a reference. The lifetime of presentable images is already complex enough.

2) Should the `srcRect` and `dstRect` parameters be specified as part of the present command, or at swapchain creation time?

RESOLVED: As part of the presentation command. This allows moving and scaling the image on the screen without the need to respecify the mode or create a new swapchain and presentable images.

3) Should `srcRect` and `dstRect` be specified as rects, or separate offset/extent values?

RESOLVED: As rects. Specifying them separately might make it easier for hardware to expose support for one but not the other, but in such cases applications must just take care to obey the reported capabilities and not use non-zero offsets or extents that require scaling, as appropriate.

4) How can applications create multiple swapchains that use the same images?

RESOLVED: By calling vkCreateSharedSwapchainsKHR.

An earlier resolution used vkCreateSwapchainKHR, chaining multiple VkSwapchainCreateInfoKHR structures through `pNext`. In order to allow each swapchain to also allow other extension structs, a level of indirection was used: VkSwapchainCreateInfoKHR::`pNext` pointed to a different structure, which had both `sType` and `pNext` members for additional extensions, and also had a pointer to the next VkSwapchainCreateInfoKHR structure. The number of swapchains to be created could only be found by walking this linked list of alternating structures, and the `pSwapchains` out parameter was reinterpreted to be an array of VkSwapchainKHR handles.

Another option considered was a method to specify a “shared” swapchain when creating a new swapchain, such that groups of swapchains using the same images could be built up one at a time. This was deemed unusable because drivers need to know all of the displays an image will be used on when determining which internal formats and layouts to use for that image.

### Examples

| Note The example code for the `VK_KHR_display` and `VK_KHR_display_swapchain` extensions was removed from the appendix after revision 1.0.43. The display swapchain creation example code was ported to the cube demo that is shipped with the official Khronos SDK, and is being kept up-to-date in that location (see: https://github.com/KhronosGroup/Vulkan-Tools/blob/master/cube/cube.c).

### Version History

- Revision 1, 2015-07-29 (James Jones)

  - Initial draft

- Revision 2, 2015-08-21 (Ian Elliott)

  - Renamed this extension and all of its enumerations, types, functions, etc. This makes it compliant with the proposed standard for Vulkan extensions.

  - Switched from "revision" to "version", including use of the VK_MAKE_VERSION macro in the header file.

- Revision 3, 2015-09-01 (James Jones)

  - Restore single-field revision number.

- Revision 4, 2015-09-08 (James Jones)

  - Allow creating multiple swap chains that share the same images using a single call to vkCreateSwapChainKHR().

- Revision 5, 2015-09-10 (Alon Or-bach)

  - Removed underscores from SWAP_CHAIN in two enums.

- Revision 6, 2015-10-02 (James Jones)

  - Added support for smart panels/buffered displays.

- Revision 7, 2015-10-26 (Ian Elliott)

  - Renamed from VK_EXT_KHR_display_swapchain to VK_KHR_display_swapchain.

- Revision 8, 2015-11-03 (Daniel Rakos)

  - Updated sample code based on the changes to VK_KHR_swapchain.

- Revision 9, 2015-11-10 (Jesse Hall)

  - Replaced VkDisplaySwapchainCreateInfoKHR with vkCreateSharedSwapchainsKHR, changing resolution of issue #4.

- Revision 10, 2017-03-13 (James Jones)

  - Closed all remaining issues. The specification and implementations have been shipping with the proposed resolutions for some time now.

  - Removed the sample code and noted it has been integrated into the official Vulkan SDK cube demo.

## See Also

VkDisplayPresentInfoKHR, vkCreateSharedSwapchainsKHR

## Document Notes

For more information, see the Vulkan Specification

This page is a generated document. Fixes and changes should be made to the generator scripts, not directly.

## Copyright

Copyright (c) 2014-2020 The Khronos Group Inc.

SPDX-License-Identifier: CC-BY-4.0