Macro rendy_core::rendy_backend

macro_rules! rendy_backend {
    (match ($target:expr) : $enum_type:path {
        $(Dx12 => $dx12_code:block)?
        $(Empty => $empty_code:block)?
        $(Gl => $gl_code:block)?
        $(Metal => $metal_code:block)?
        $(Vulkan => $vulkan_code:block)?
        $($(use $back:ident;)?_ => $code:block)?
    }) => { ... };
    (match ($target:expr) : $enum_type:path {
        $(Dx12($dx12_pat:pat) => $dx12_code:block)?
        $(Empty($empty_pat:pat) => $empty_code:block)?
        $(Gl($gl_pat:pat) => $gl_code:block)?
        $(Metal($metal_pat:pat) => $metal_code:block)?
        $(Vulkan($vulkan_pat:pat) => $vulkan_code:block$)?
        $($(use $back:ident;)?_($pat:pat) => $code:block)?
    }) => { ... };
}

Execute arm with matching backend. If particular backend is disabled then its arm is stripped from compilation altogether.