VK_KHR_pipeline_binary internal cache check example should elaborate that VK_EXT_shader_module_identifier (or similar) is required

[elasota]

Vulkan-Docs/proposals/VK_KHR_pipeline_binary.adoc

Line 261 in 98b6c43

When `pipelineBinaryInternalCache` is supported it is possible to create pipeline binaries using just the pipeline create info, without providing either SPIR-V or binary data, by

"it is possible to create pipeline binaries using just the pipeline create info, without providing either SPIR-V or binary data"

The example uses an empty VkGraphicsPipelineCreateInfo. Presumably the create info would be filled out, but I think this example is unclear because there is no valid way to provide a key without also providing the binary data, so the key is not a substitute for a module identifier in this case, and there is no way to just probe the internal cache for the presence of specific keys (or sets of keys).

I think the only way that feature works is with VK_EXT_shader_module_identifier? I think it would be helpful to elaborate that.

(It sure would be nice if there was a way to just do this by passing a list of keys, since they are supposed to be unique identifiers, but the spec doesn't currently permit that.)

[radiosityy]

I am just looking into pipeline binaries and you hit the nail on the head. This is the exact problem I've been wondering about for a couple days as it looks like the only way to get pipeline binaries from the pipeline binary internal cache is by loading the spir-v bytecode in the first place to fill the VkGraphicsPipelineCreateInfo.pStages, which seems super inefficient. I agree that it seems like we should be able to just provide a pipeline key to get pipeline binaries from the internal cache, rather than having to provide a whole VkGraphicsPipelineCreateInfo struct with shader modules (containing spir-v) included. At the moment, ignoring the internal cache and maintaining an application cache seems like a much better option since you can just directly load the binaries for specific pipelines/pipeline keys from disk and use them immediately without doing a complex internal cache query with VkGraphicsPipelineCreateInfo.
Whether you can use VK_EXT_shader_module_identifier is something I've been wondering about as it's not stricly stated and described anywherer in the spec or the docs (at least i haven't seen it). The thing is, VK_EXT_shader_module_identifier works strictly with the regular pipeline cache and, in general, pipeline cache and pipeline binary cache seem to be a bit at odds with each other (e.g. you can't use both at the same time for pipeline creation as they are exclusive), so I wasn't certain if you can use it correctly in this context. And even if you could, it seems to add a bunch of extra work to generate these identifiers beforehand, store them on disk and then also retrieve them and associate them with particular pipelines. Again - maintaining an application cache and ignoring the internal cache just seems way easier and less cumbersome and more efficient.
I wonder if there's a reason why we can't query the pipeline binaries with pipeline keys instead of VkGraphicsPipelineCreateInfo?