Update vulkan example

[exrook]

Example now renders in 3D using the tracked HMD position and shows cubes at the location of each hand controller.

[Ralith]

Align isn't doing anything useful here.

[exrook]

What do you recommend instead? I did it this way because this is what I saw in the ash examples. (and I changed it again to use vertex_buffer_mem_requirements.alignment for the second argument in the force push I just did but I suspect that may have been incorrect after doing some more research)

[Ralith]

You shouldn't need to do anything special at all. Memory allocated according to the requirements of a vertex buffer will necessarily satisfy the buffer's GPU-side alignment requirements. I believe the CPU-side alignment should also be implicitly satisfied. Writing data starting at any location other than the start of the buffer, or with a non-dense stride, would constitute a mismatch with the vertex attribute layout declared in the pipeline.

[Ralith]

(unfortunately the ash examples, and indeed most introductory vulkan examples, aren't great; there's a PR in need of review to improve them)

[exrook]

Would it be sound to construct an &mut [T] from gpu memory or should I always go through ptr:;write?

[exrook]

I see Align does create a slice but my concern is that the data in the buffer may not be valid for reads. I think I'll use std::ptr::copy for now.

[Ralith]

Creating a slice to uninitialized memory would be unsound, yeah. copy_nonoverlapping should be preferred.

[exrook]

Sounds good