Refactor getting/adding extension features to create a VkDevice with.

[asuessenbach]

Description

As described in #938, requesting and enabling extension features is currently incorrect. With this PR, this is done similar to how it's done for the simple PhysicalDeviceFeatures: one function to get the supported bits (get_extension_features) and one to actually set them into the structure chain (add_extension_features).
The perfect handling would look like this:

if (gpu.get_extension_features<VkExtensionFeaturesStruct>(VK_STRUCTURE_TYPE_EXTENSION_FEATURES_STRUCT).featureBit)
{
	gpu.add_extension_features<VkExtensionFeaturesStruct>(VK_STRUCTURE_TYPE_EXTENSION_FEATURES_STRUCT).featureBit = VK_TRUE;
}
else
{
	// some fallback or error handling!
}

To ease usage, [HPP]PhysicalDevice got two new template functions: request_optional_feature and request_required_feature, which log a message or throw an exception, respectively, if the requested feature is not supported.
Requesting a required feature would now look like

gpu.request_required_feature<VkExtensionFeaturesStruct>(VK_STRUCTURE_TYPE_EXTENSION_FEATURES_STRUCT,
                                                        &VkExtensionFeaturesStruct::featureBit,
                                                        "VkExtensionFeaturesStruct",
                                                        "featureBit");

Where the last two arguments to that functions are just for error reporting and maybe could omitted.

To ease usage even more, some macros have been added, so that requesting a required feature would now look like

REQUEST_REQUIRED_FEATURE(gpu, VkExtensionFeaturesStruct, VK_STRUCTURE_TYPE_EXTENSION_FEATURES_STRUCT, featureBit);

Build tested on Win10 with VS2022. Run tested on Win10 with NVidia GPU.

Fixes #938

General Checklist:

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• I have tested every sample to ensure everything runs correctly
• This PR describes the scope and expected impact of the changes I am making

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• I have tested the sample on at least one compliant Vulkan implementation
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[gary-sweet]

I don't think we can just assert in all these cases can we?
It seems to prevent batch mode from running as soon as it finds an unsupported case.

[asuessenbach]

I don't think we can just assert in all these cases can we?

You're kind of right. As I stated in the Description above, that should be replaced by some meaningful error or fall-back handling.
What would you suggest to do instead until then?

[gary-sweet]

What would you suggest to do instead until then?

Well throwing a std::runtime_error would be better, as it doesn't terminate batch mode, just the current sample I guess.

I'm also not really sure what was wrong with just having a single call to request_extension_features? I can't see why unrolling that code everywhere is better. Maybe I'm just missing the issue that's being solved here.

[asuessenbach]

I'm also not really sure what was wrong with just having a single call to request_extension_features?

The problem, as described in #938, was, that currently you get the supported extension features bits, possibly set some of them to true, no matter if they are supported at all, and store that structure in the structure chain for device creation.
That is, there are two issues:

• All supported flags are requested, no matter if you actually need/want the support of all those flags.
• Potentially support of a not supported feature is requested.

With this PR, you just set the flags you're interested in and when they're supported at all.

[asuessenbach]

Well throwing a std::runtime_error would be better, as it doesn't terminate batch mode, just the current sample I guess.

Sounds good. I can change that accordingly.

[gary-sweet]

I think you'll need to rebase this over #1031. A lot of the samples don't run without that, so testing this isn't really possible without it.

[SaschaWillems]

Tbh. I'm kinda torn over the syntax that now needs to be used. Will that actually work with e.g. code completion/intellisense? Or will it fail at compile time when I e.g. request a member of a feature that isn't present or that I did misspell?

I'm referring to this:

REQUEST_REQUIRED_FEATURE(gpu,
VkPhysicalDeviceGraphicsPipelineLibraryFeaturesEXT,
VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_GRAPHICS_PIPELINE_LIBRARY_FEATURES_EXT,
graphicsPipelineLibrary);

The old syntax has you access that member (graphicsPipelineLibary) directly, which works fine with intellisense/code compleation and is easier to understand/follow:

auto &requested_vertex_input_features      = gpu.request_extension_features<VkPhysicalDeviceMeshShaderFeaturesEXT>(VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_MESH_SHADER_FEATURES_EXT);
requested_vertex_input_features.meshShader = VK_TRUE;

(though I don't really like that syntax either)

I fear that this makes working on samples harder, hurts readability and foremost makes it harder to follow our samples.

Is there a different way to handle this that looks more similar to the old syntax?

[asuessenbach]

Will that actually work with e.g. code completion/intellisense?

As it is with all macros, you probably don't have any support by code completion or intellisense when you use [HPP_]REQUEST_[OPTIONAL|REQUIRED]_FEATURE. Any error will fire up at compile time.
When you use the helper functions gpu.request_[optional|required]_feature or the actual worker functions gpu.[add|get]_extension_features, you of course have all the help available by code completion and intellisense.

The old syntax has you access that member (graphicsPipelineLibary) directly, which works fine with intellisense/code compleation and is easier to understand/follow:

But as described in #938 it's just wrong!

Is there a different way to handle this that looks more similar to the old syntax?

I don't know of any.

Actually, I provided three different levels of complexity to handle that correctly. If you have an idea for an additional approach, I'd be happy to add that as well.

[SaschaWillems]

As discussed on the call, here is the way I do it in my samples:

• I declare the extension struct(s) in the sample
• I setup the whole extension struct(s) in the sample constructor
• I add the struct(s) to a pNext pointer of my device / instance

An example:

class VulkanExample : public VulkanExampleBase
{
    VkPhysicalDeviceTimelineSemaphoreFeaturesKHR enabledTimelineSemaphoreFeaturesKHR{};

    VulkanExample() : VulkanExampleBase()
    {
        ...

        enabledTimelineSemaphoreFeaturesKHR.sType = VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_TIMELINE_SEMAPHORE_FEATURES_KHR;
        enabledTimelineSemaphoreFeaturesKHR.timelineSemaphore = VK_TRUE;

        pNextDevice = &enabledTimelineSemaphoreFeaturesKHR;
    }    

}

It might not be the best approach from a C++ language point of view (esp. how pNextDevice is implemented), but it makes it very easy for people to follow my samples and you can copy that 1:1 into your own application without having to follow any templates or macros.

It would probably be a more substantial change, so before we take this further we should agree on what way we want to follow.

[asuessenbach]

@SaschaWillems I assume, that pNextDevice is the pNext of some VkPhysicalDeviceFeatures2, that you hold somewhere. And you're using a pointer to that VkPhysicalDeviceFeatures2 to create a VkDevice using vkCreateDevice().
That is, it seems that setting the requested features and actually using that is also distributed to (at least) two separate code sequences.
But, what's more important, I don't see that you first ask if the requested feature actually is supported. You would need a second structure chain to first ask for support using vkGetPhysicalDeviceFeatures2().

From a sample point of view, I think, it's important that the reader of the sample can easily see what features are requested. But I would not consider the details on how that is handled to be important for a sample. Besides for a sample that actually demonstrates how feature requesting is done, of course.

[SaschaWillems]

But, what's more important, I don't see that you first ask if the requested feature actually is supported. You would need a second structure chain to first ask for support using vkGetPhysicalDeviceFeatures2().

I actually don't do that. If one requests a feature that isn't supported, instance or device creation will fail with an error code hinting at a feature not supported. I want to deliberately keep samples as simple as possible.

[asuessenbach]

If one requests a feature that isn't supported, instance or device creation will fail with an error code hinting at a feature not supported.

Interesting approach! That is, you would get some VK_ERROR_FEATURE_NOT_PRESENT on vkCreateDevice and bail out at that point. But you can't tell then, what feature is missing. And how would you handle some optionally used feature?
I would consider to first get the supported features and potentially react accordingly on their absence the "cleaner" and also more descriptive way to handle that.
And I don't think, that code is that much harder to read and understand.