There are a number of shaders, most notably grid_frag.glsl, which rely on default assignments to uniform values within shaders. This is not currently supported by the shader uniform push model implemented for the Metal backend, wherein uniform updates are pushed as a singular block of data. Any default assignment would become over-written.
As such, adding assignments of these default values in the high-level, to ensure the correct value is written for all APIs. This likely impacts Vulkan push-constants as well.
Authored by Apple: Michael Parkin-White
Ref T96261
Reviewed By: fclem
Maniphest Tasks: T96261
Differential Revision: https://developer.blender.org/D14555
db622b5a0b