Zero-initialization zeroes out all members and padding bits, so this is
safe to do. While we're at it, also add static assertions that enforce
the necessary requirements of a UID type explicitly within the ShaderUid
class.
This way, we can remove several memset calls around the shader
generation code that makes sure the underlying UID data is zeroed out.
Now our ShaderUid class enforces this for us, so we don't need to care about
it at the usage sites.
The Metal shader compiler fails to compile the atomic instructions
when operating on individual components of a vector. Spltting it
into four variables shouldn't make any difference for other
platforms, as they are accessed independently.
floatindex is clamped to the range [0, 9]. For non-negative numbers
floor() is equivalent to trunc(). Truncation happens implicitly when
converting to uint, so the floor() is unnecessary.
Tested on a linux Intel Skylake integrated graphics with
blend_func_extended force-disabled, as it's the only platform I have
that doesn't crash with ubershaders and supports fb_fetch
Currently, this is only the logic op bit, but this will be extended to
the framebuffer fetch/blend modes. In the future, when/if we move to
VideoCommon pipelines, this state will be part of the pipeline UID
anyway, and we can mask it out in the backend by using a two-level map,
so the shaders/programs are shared.
The switch statements in these functions appear to get transformed into
an if..else chain on NVIDIA's OpenGL/Vulkan drivers, resulting in lower
performance than the D3D counterparts. Transforming the switch into a
binary tree of ifs can increase performance by up to 20%.
