windowSize / currentExtent vkGetPhysicalDeviceSurfaceCapabilitiesKHR

[buhman]

Swapchain

This wording (emphasis added)

First step is getting the correct extent of the swapchain.

Is confusing.

docs.vulkan.org/VkSwapchainCreateInfoKHR says:

imageExtent [...] The behavior is platform-dependent if the image extent does not match the surface’s currentExtent as returned by vkGetPhysicalDeviceSurfaceCapabilitiesKHR.

However, later, in the if (updateSwapchain) block, imageExtent is changed to windowSize on a window resize.

Suggestion: do one of these things:

• delete the if (surfaceCaps.currentExtent.width == 0xFFFFFFFF) block and set the value of swapchainExtent to the value of windowSize (both in the tutorial text and in the source code); remove the entire paragraph that starts with the sentence "First step is getting the correct extent of the swapchain."
• improve the explanation in "Swapchain" and/or "Recreate swapchain" with more detail on the reason for apparent inconsistency in (not) comparing currentExtent as returned by vkGetPhysicalDeviceSurfaceCapabilitiesKHR with the window size as returned by SDL_GetWindowSize.
• if the current "Recreate swapchain" implementation is incorrect, and it should indeed use the extent values from vkGetPhysicalDeviceSurfaceCapabilitiesKHR when possible, modify the "Recreate swapchain" implementation to do so (both in the tutorial text and in the source code).

[buhman]

I observed on my platform that at times during a window resize the value returned by SDL_GetWindowSize does not match the value returned by vkGetPhysicalDeviceSurfaceCapabilitiesKHR. When this happens, Vulkan Validation Layers emits a validation error:

Validation Error: [ VUID-VkSwapchainCreateInfoKHR-pNext-07781 ] | MessageID = 0x4c8929c1
vkCreateSwapchainKHR(): pCreateInfo->imageExtent (width = 1280, height = 687), which is outside the bounds returned by vkGetPhysicalDeviceSurfaceCapabilitiesKHR(): currentExtent = (width = 1280, height = 686), minImageExtent = (width = 1280, height = 686), maxImageExtent = (width = 1280, height = 686).
The Vulkan spec states: If a VkSwapchainPresentScalingCreateInfoKHR structure was not included in the pNext chain, or it is included and VkSwapchainPresentScalingCreateInfoKHR::scalingBehavior is zero then imageExtent must be between minImageExtent and maxImageExtent, inclusive, where minImageExtent and maxImageExtent are members of the VkSurfaceCapabilitiesKHR structure returned by vkGetPhysicalDeviceSurfaceCapabilitiesKHR for the surface (https://docs.vulkan.org/spec/latest/chapters/VK_KHR_surface/wsi.html#VUID-VkSwapchainCreateInfoKHR-pNext-07781)

It seems likely to be more correct to always use currentExtent as the value of swapchainCI.imageExtent if the width/height are not both 0xFFFFFFFF for swapchain re-creation.