Pad FixedPipelineState's size to 384 bytes to be a multiple of 16.
Compare the whole struct with std::memcmp and hash with CityHash. Using
CityHash instead of a naive hash should reduce the number of collisions.
Improve used type traits to ensure this operation is safe.
With these changes the improvements to the hashable pipeline state are:
Optimized structure
Hash: 89 ns
Comparison: 103 ns
Construction*: 164 ns
Struct size: 384 bytes
Original structure
Hash: 148 ns
Equal: 174 ns
Construction*: 281 ns
Size: 1384 bytes
* Attribute state initialization is not measured
These measures are averages taken with std::chrono::high_accuracy_clock
on MSVC shipped on Visual Studio 16.6.0 Preview 2.1.
The intention behind this hasheable structure is to describe the state
of fixed function pipeline state that gets compiled to a single graphics
pipeline state object. This is all dynamic state in OpenGL but Vulkan
wants it in an immutable state, even if hardware can edit it freely.
In this commit the structure is defined in an optimized state (it uses
booleans, has paddings and many data entries that can be packed to
single integers). This is intentional as an initial implementation that
is easier to debug, implement and review. It will be optimized in later
stages, or it might change if Vulkan gets more dynamic states.
