Use cases for synchronization

Hey all,

During the memory barriers discussion we said it would be nice to look at
specific examples, and how they map to different APIs. The Vulkan WG has
made a small list of examples
<https://github.com/KhronosGroup/Vulkan-Docs/wiki/Synchronization-Examples>
to help developers do synchronization when porting to Vulkan. They show
real-world things developers want to do, and how it maps to Vulkan on a
single queue:

   - Compute-to-Compute
      - *First dispatch writes to buffer, second reads from it*
      - First dispatch reads from a buffer, second writes to it
      - Same for images
      - First and second dispatches write to non-overlapping regions of
      same buffer and third dispatch reads from both regions.
      - First and second dispatches write to two buffers, third dispatch
      reads from both buffers.
   - Compute-to-Graphics
      - *Dispatch writes to buffer, draw reads from it as index buffer.*
      - Dispatch writes to buffer, draw reads from it as index buffer and
      other dispatch reads as uniform buffer.
      - Dispatch writes to buffer, draw reads from it as indirect buffer.
      - *Dispatch writes to image, draw samples image.*
      - Dispatch writes to texel buffer, draw reads from it as indirect and
      uniform buffer
   - Graphics-to-Compute
      - *Draw writes to color / depth attachment, dispatch reads from
      image.*
   - Graphics-to-Graphics
      - *First draw writes depth / color attachment, second draw samples as
      input attachment (i.e. from tile memory)*
      - First draw writes depth / color attachment, second samples in
      fragment shader.
      - First draw samples texture, second draw uses texture as color
      attachment.

They don't go in as much detail for multi-queue stuff, but I believe a lot
of the example with both graphics and compute would be interesting to map
to multiple queues too.

In bold are the use-cases that I believe are important / a good sample and
we could focus on. The page linked already has the examples for Vulkan.

Cheers,

Corentin