vkGetPhysicalDeviceDisplayPropertiesKHR returns 0 displays always

Question

I am working on a small example using Vulkan. On my laptop there is a special case by having two GPUs (Intel UHD + Nvidia Quadro T1000). I want to achieve the same thing as DXGI provides by enumerating all adapters and all possible outputs to make sure to select the correct screen.

What I did:

• I additionally added VK_KHR_display extension to VkInstanceCreateInfo structure
• call to vkCreateInstance
• call to vkEnumeratePhysicalDevices twice to get number and all physical devices.
• call to vkGetPhysicalDeviceDisplayPropertiesKHR for each physical device

In any case vkGetPhysicalDeviceDisplayPropertiesKHR returns 0 as number of displays.

Tested on Vulkan SDK 1.3.204.1

• Ubuntu 20.04 inside a VBox VM (yes, it works with Lavapipe) using latest Vulkan SDK
• Windows 10

Both behave the same by returning 0. Is there anything special to observe?

Answer 1

This is probably happening because there is no "free" display monitor on your system for the VK_KHR_display extension to use. This extension is intended to draw to a display that is not under the control of a window or display manager.

In your case, you can plug a monitor into your laptop and configure the OS to NOT use it. Windows will automatically extend or duplicate your desktop to the external monitor, so you'll need to go into the display settings and tell it to remove that display.

This example sort of shows how to do it. The example shows off other stuff by using OpenGL to render something and then have Vulkan draw it to a VK_KHR_display display. But it is this last step that counts and there are clear instructions on how to free up a monitor on Windows.

Technically, getting a count of zero is correct in your case since there are no VK_KHR_display displays available. If you plug in a non-managed monitor, then you should see something other than zero. And all this seems reasonable for your enumeration task.