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VK_KHR_display_swapchain

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

New Structures

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 presentation 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

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/main/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 swapchains 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.