Function clipper_path64_minkowski_diff 

pub unsafe extern "C" fn clipper_path64_minkowski_diff(
    mem: *mut c_void,
    pattern: *mut ClipperPath64,
    path: *mut ClipperPath64,
    is_closed: c_int,
) -> *mut ClipperPaths64

Minkowski difference: like clipper_path64_minkowski_sum but translates pattern by -p instead of +p at each vertex of path. For a pattern that is symmetric about the origin (e.g. a centred disc or square) sum and difference produce the same result; the distinction matters as soon as the pattern is asymmetric, where difference is the operation you want for “set of points x such that x + pattern is contained in path” intuitions (robot-footprint configuration space, tool-reachability inside a pocket).

Same memory contract as clipper_path64_minkowski_sum.