gfx::gfx_defines!

macro_rules! gfx_defines {
    (vertex $name:ident {
            $( $field:ident : $ty:ty = $e:expr, )+
    }) => { ... };
    (constant $name:ident {
            $( $field:ident : $ty:ty = $e:expr, )+
    }) => { ... };
    (pipeline $name:ident {
            $( $field:ident : $ty:ty = $e:expr, )+
    }) => { ... };
    ($keyword:ident $name:ident {
            $( $field:ident : $ty:ty = $e:expr, )+
    } $($tail:tt)+) => { ... };
}

Defines vertex, constant and pipeline formats in one block