```cmake
find_path(Clipper_INCLUDE_DIR polyclipping/clipper.hpp)
find_library(Clipper_LIBRARIES polyclipping)

include(FindPackageHandleStandardArgs)

find_package_handle_standard_args(Clipper Clipper_INCLUDE_DIR Clipper_LIBRARIES)
```

Use PkgConfig to finde Clipper.
user
```cmake
# - Try to find Clipper
# Once done this will define
#  Clipper_FOUND - System has Clipper
#  Clipper_INCLUDE_DIRS - The Clipper include directories
#  Clipper_LIBRARIES - The libraries needed to use Clipper
#  Clipper_DEFINITIONS - Compiler switches required for using Clipper

find_package(PkgConfig)
pkg_check_modules(PC_Clipper QUIET polyclipping.pc)
set(Clipper_DEFINITIONS ${PC_Clipper_CFLAGS_OTHER})

find_path(Clipper_INCLUDE_DIR polyclipping/clipper.hpp
  HINTS ${PC_Clipper_INCLUDEDIR} ${PC_Clipper_INCLUDE_DIRS}
  PATH_SUFFIXES libpolyclipping)

find_library(Clipper_LIBRARY NAMES polyclipping libpolyclipping
  HINTS ${PC_Clipper_LIBDIR} ${PC_Clipper_LIBRARY_DIRS} )

include(FindPackageHandleStandardArgs)
# handle the QUIETLY and REQUIRED arguments and set Clipper_FOUND to TRUE
# if all listed variables are TRUE
find_package_handle_standard_args(Clipper  DEFAULT_MSG
  Clipper_LIBRARY Clipper_INCLUDE_DIR)

mark_as_advanced(Clipper_INCLUDE_DIR Clipper_LIBRARY)

set(Clipper_LIBRARIES ${Clipper_LIBRARY})
set(Clipper_INCLUDE_DIRS ${Clipper_INCLUDE_DIR})
```
assistant