Fix fragment_shading_rate_dynamic sample

[jherico]

Description

Fix the declaration of the compute_buffer in a loop as an r-value reference to a simple reference.

Fixes #913

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[SaschaWillems]

Sorry, was a bit hasty with my approval. Even with this fix applied, the sample crashes for me with the following error:

error] [framework\core\instance.cpp:50] -1360208885 - VUID-vkQueueSubmit-pCommandBuffers-00070: Validation Error: [ VUID-vkQueueSubmit-pCommandBuffers-00070 ] Object 0: handle = 0x247718630e0, type = VK_OBJECT_TYPE_COMMAND_BUFFER; | MessageID = 0xaeecdc0b | vkQueueSubmit(): pSubmits[0].pCommandBuffers[0] VkCommandBuffer 0x247718630e0[] is unrecorded and contains no commands. The Vulkan spec states: Each element of the pCommandBuffers member of each element of pSubmits must be in the pending or executable state (https://vulkan.lunarg.com/doc/view/1.3.275.0/windows/1.3-extensions/vkspec.html#VUID-vkQueueSubmit-pCommandBuffers-00070)

[SaschaWillems]

I'm actually not sure why that sample works at all. It allocates the compute command buffers from the base class command pool, which may be limited to the graphics queue family index.

Imo it should be adjusted to create it's own compute command pool, like we do in the other compute related samples.

[jherico]

I'm actually a bit confused, because I recently did a batch test against my allocated-refactor branch which does NOT have this fix and it passed without crashing. And the error you're seeing is what I was getting before I made this change on the sample, so I think the sample is more subtle than I suspected at first...

Imo it should be adjusted to create it's own compute command pool, like we do in the other compute related samples.

I initially tried that approach because I noticed that FragmentShadingRateDynamic::build_command_buffers resets this command pool, which invalidates any of the compute buffers allocated from it, but that didn't seem to help. That's also where my investigation with git bisect led me.

I'm going to give that another shot and test it again checking both release and debug modes this time.

[jherico]

OK, so using a dedicated compute queue for the compute operations would require significant refactoring of the example. While the acquire and release barriers in the compute command buffers are pretty straight-forward, it's not immediately clear to me where they'd go on the graphics side. It looks like the acquire would have to go in the draw_cmd_buffers but the release would have to go in the small_command_buffers, I think. At any rate, I'm going to just try to resolve this with a unified queue for now.