By default, the matrix would be declared as mediump, causing precision
issues. Need to dispatch to two separate functions since GLSL does not
support overload based on precision.
We'll need to force a temporary and mark it as precise.
MSL is a little weird here, but we can piggyback on top of the invariant
float math option here to force fma() operations everywhere.
Avoids certain cases of variance between translation units by forcing
every dependent expression of a store to be temporary.
Should avoid the major failure cases where invariance matters.
