* This is a stupid requirement as the quad overdraw shader doesn't use any
interpolators, but the D3D12 runtime complains and refuses to create a PSO
unless the PS has a matching signature. This works as long as the position was
the first output from the previous stage, but if it isn't the PSO fails to
create.
* To fix this, we take the existing shader and patch it by grafting the output
signature from the last stage over onto the input signature, and patching up
where the position is.
* There's not a good accepted terminology for this kind of event, and for
historical reasons 'drawcall' has been the accepted term, even though
that can be quite confusing when a dispatch or a copy is a 'drawcall'.
* This is particularly highlighted by the event browser filters where
$draw() includes draws and dispatches, but $dispatch() only includes
dispatches, it's hard to intuitively understand why $draw() matches all
of these calls.
* As a result we've defined the term 'action' to cover these types of
events in the same way that we defined 'event' in the first place to
mean a single atomic API call.
* We need to copy the external-facing m_RenderState into the partial command
buffer's state for partial replay, in case it was modified externally.
* Also when accessing the render state inside a drawcall callback we need to use
the command buffer's local state, not m_RenderState which isn't updated until
the replay completes.
baldurk