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VK_KHR_incremental_present

Other Extension Metadata

Last Modified Date

2016-11-02

IP Status

No known IP claims.

Contributors
  • Ian Elliott, Google
  • Jesse Hall, Google
  • Alon Or-bach, Samsung
  • James Jones, NVIDIA
  • Daniel Rakos, AMD
  • Ray Smith, ARM
  • Mika Isojarvi, Google
  • Jeff Juliano, NVIDIA
  • Jeff Bolz, NVIDIA

Description

This device extension extends vkQueuePresentKHR, from the VK_KHR_swapchain extension, allowing an application to specify a list of rectangular, modified regions of each image to present. This should be used in situations where an application is only changing a small portion of the presentable images within a swapchain, since it enables the presentation engine to avoid wasting time presenting parts of the surface that have not changed.

This extension is leveraged from the EGL_KHR_swap_buffers_with_damage extension.

New Structures

New Enum Constants

  • VK_KHR_INCREMENTAL_PRESENT_EXTENSION_NAME
  • VK_KHR_INCREMENTAL_PRESENT_SPEC_VERSION
  • Extending VkStructureType:
    • VK_STRUCTURE_TYPE_PRESENT_REGIONS_KHR

Issues

1) How should we handle steroescopic-3D swapchains? We need to add a layer for each rectangle. One approach is to create another struct containing the VkRect2D plus layer, and have VkPresentRegionsKHR point to an array of that struct. Another approach is to have two parallel arrays, pRectangles and pLayers, where pRectangles[i] and pLayers[i] must be used together. Which approach should we use, and if the array of a new structure, what should that be called?

RESOLVED: Create a new structure, which is a VkRect2D plus a layer, and will be called VkRectLayerKHR.

2) Where is the origin of the VkRectLayerKHR?

RESOLVED: The upper left corner of the presentable image(s) of the swapchain, per the definition of framebuffer coordinates.

3) Does the rectangular region, VkRectLayerKHR, specify pixels of the swapchain’s image(s), or of the surface?

RESOLVED: Of the image(s). Some presentation engines may scale the pixels of a swapchain’s image(s) to the size of the surface. The size of the swapchain’s image(s) will be consistent, where the size of the surface may vary over time.

4) What if all of the rectangles for a given swapchain contain a width and/or height of zero?

RESOLVED: The application is indicating that no pixels changed since the last present. The presentation engine may use such a hint and not update any pixels for the swapchain. However, all other semantics of vkQueuePresentKHR must still be honored, including waiting for semaphores to signal.

5) When the swapchain is created with VkSwapchainCreateInfoKHR::preTransform set to a value other than VK_SURFACE_TRANSFORM_IDENTITY_BIT_KHR, should the rectangular region, VkRectLayerKHR, be transformed to align with the preTransform?

RESOLVED: No. The rectangular region in VkRectLayerKHR should not be transformed. As such, it may not align with the extents of the swapchain’s image(s). It is the responsibility of the presentation engine to transform the rectangular region. This matches the behavior of the Android presentation engine, which set the precedent.

Version History

  • Revision 1, 2016-11-02 (Ian Elliott)
    • Internal revisions
  • Revision 2, 2021-03-18 (Ian Elliott)
    • Clarified alignment of rectangles for presentation engines that support transformed swapchains.