Month 2 - Part 1

Over the past week I was working on a Vulkan validation error that was caused by some weird environment setup on my machine. The error was complaining about not knowing what a specific struct type was when chaining features on in our CreateVkDevice() method in this section of the code:

What was happening was the requested API got set to 1.3 but 1.4 was defined so when it would hit the #if defined(VK_API_VERSION_1_4) it would try to chain on the 1.4 feature struct but was using the 1.3 validation layers which were too old to recognize this newer struct.

Validation layers in Vulkan are meant as a debug tool to tell you when your pipeline/set up is off and helps debug issues early before they become a problem in release. Despite the message, everything got set up correctly and I couldn't reproduce the issue reliably so Lari and I decided that it would be best to move on as it was probably a user error in how I set up the project and my environment variables.

I then moved on to an issue reported to us by Justin Edwards:
VUID-VkDeviceCreateInfo-pNext-02830(ERROR / SPEC): msgNum: 555635515 - Validation Error: [ VUID-VkDeviceCreateInfo-pNext-02830 ] Object 0: handle = 0x25a8407cc70, type = VK_OBJECT_TYPE_INSTANCE; | MessageID = 0x211e533b | vkCreateDevice(): If the pNext chain includes a VkPhysicalDeviceVulkan12Features structure, then it must not include a VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_DESCRIPTOR_INDEXING_FEATURES structure

Which is complaining about 12 including the VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_DESCRIPTOR_INDEXING_FEATURES structure which comes from this part in our code:

Where before we didn't have the:

#if defined(VK_API_VERSION_1_2)

features12.descriptorIndexing = VK_TRUE;

#else

but with the new if define we're basically saying if we're on 1.2 or higher then we don't want to add that flag which ended up fixing the issue.

To ensure this fix was working we asked Justin for his exact setup and I created a test case mimicking this which looks like:

Which also accounts for the other versions of Vulkan. This test reproduced his errors without the fix and didn't produce them with it which proved our fix was working. He then downloaded the new Gateware version and tested it, confirming that it cleared that error but still produced this:

I'll be looking into what's causing this validation error along with tackling these tasks:

Which should provide some good learning opportunities for me.

Month 1 - Part 2

Over the past couple of weeks I've been working on a Vulkan issue that could happen if the user had Vulkan tooling installed that was on a lower version of the API than their drivers claimed they could support. I figured this out when I tried to build the project requesting Vulkan SDK v1.3.296.0 while my drivers supported 1.4+. The error message I got was:

VUID-VkDeviceCreateInfo-pNext-pNext(ERROR / SPEC): msgNum: -1876993556 - Validation Error: [ VUID-VkDeviceCreateInfo-pNext-pNext ] | MessageID = 0x901f59ec | vkCreateDevice(): pCreateInfo->pNext chain includes a structure with unknown VkStructureType (55). This error is based on the Valid Usage documentation for version 296 of the Vulkan header. It is possible that you are using a struct from a private extension or an extension that was added to a later version of the Vulkan header, in which case the use of pCreateInfo->pNext is undefined and may not work correctly with validation enabled. The Vulkan spec states: Each pNext member of any structure (including this one) in the pNext chain must be either NULL or a pointer to a valid struct for extending VkDeviceCreateInfo

Which basically means "I don't know what VkStructureType (55) is because it's not defined on this API version."

I eventually figured out that we were chaining feature structs up to the highest available version the users machine could run instead of what we intend to target. I fixed this by choosing the minimum version between what we intend to target and what the driver supports and then using this as a check before chaining feature structs. The code snippet for this is below:

1. We get the device properties so we can see which API version our graphics drivers support

2. We check this against our requested API version and take the minimum

3. We use this as a gate for feature chaining so we don't chain anything over the requested API version

That's all of my updates for now!