VK_NV_display_stereo

The VK_KHR_display extension allows Vulkan to present directly to display devices without using an intermediate windowing system. However, on some platforms this means that there is not an easy way to configure hardware settings external to the app. There are many different types of 3D stereo hardware, and the driver needs to know which type of hardware is connected so that it can properly configure it. For some hardware, this is not automatically detectable and must be configured manually by the app or user.

Also, for the case of HDMI_3D (HDMI Frame Packed Stereo), the monitors that support this stereo type may only support stereo rendering on a subset of the display modes they advertise, and will require the application to choose the correct display mode to enable stereo rendering.

The driver could expect some configuration file or environment variable to do this selection, but that option is not very user friendly, and not very secure.

On other platforms, such as Windows or on Linux with an X compositor, there can be a GUI for this selection. But, direct display on Linux DRM can still be used without a desktop environment at all. Also, in those other environments the windowing manager controls the display mode (refresh rate and resolution) of the display, while with direct display the Vulkan app controls the display mode.

A Vulkan extension would allow the application to pick for itself what stereo 3D hardware it will be presenting to. And, it will annotate the allowed display modes for HDMI_3D.

When doing stereo rendering on direct display, the behavior of the Vulkan presentation pipeline changes in two major ways:

vkGetPhysicalDeviceSurfaceCapabilitiesKHR is a query on VkSurfaceKHR, so this extension will add the struct VkDisplaySurfaceStereoCreateInfoNV that extends VkDisplaySurfaceCreateInfoKHR. It will contain one new enum, VkDisplaySurfaceStereoTypeNV. If set, this enum will control how stereo 3D is presented on the display for this surface.

This extension will also add the struct VkDisplayModeStereoPropertiesNV that extends VkDisplayModeProperties2KHR. It will contain one bool, hdmi3DSupported, to indicate if this display mode can be used for HDMI_3D stereo rendering.

Like VUID-vkQueuePresentKHR-pSwapchains-01293 for display modes, there should only be one active stereo type for a display. There will be a similar VU on vkQueuePresentKHR that all active stereo types are the same for a display.

It is possible more types will be added in the future.

This functionality does not apply to other surface types, e.g. vkCreateWin32SurfaceKHR or vkCreateXlibSurfaceKHR, since the vulkan app does not control the display mode there like it does in direct display. Usually, stereo would be configured by the windowing manager on that platform.