Use CMake 3.5 features

1. Set `cmake_minimum_required` to 3.5 (see https://cmake.org/cmake/help/latest/release/3.27.html#id17)
2. Specify the version of CMake project
3. `cmake_policy` is called implicitly by `cmake_minimum_required` (remove its call)
4. Use `CMAKE_INSTALL_BINDIR` and `CMAKE_INSTALL_INCLUDEDIR`
5. Use Zlib as a package (automatic linking of the library and add include directory)
6. Don't activate testing if it was not enabled

CMakeLists.txt

@@ -92,7 +92,6 @@ endif()
 option(PNG_BUILD_ZLIB "Custom zlib location, else find_package is used" OFF)
 if(NOT PNG_BUILD_ZLIB)
   find_package(ZLIB REQUIRED)
-  include_directories(${ZLIB_INCLUDE_DIRS})
 endif()
 
 if(UNIX AND NOT APPLE AND NOT BEOS AND NOT HAIKU AND NOT EMSCRIPTEN)
@@ -625,7 +624,6 @@ if(PNG_DEBUG)
 endif()
 
 # Now build our targets.
-include_directories(${CMAKE_CURRENT_SOURCE_DIR} ${ZLIB_INCLUDE_DIRS})
 
 # Initialize the list of libpng library targets.
 set(PNG_LIBRARY_TARGETS "")
@@ -669,7 +667,12 @@ if(PNG_SHARED)
   if(WIN32)
     set_target_properties(png_shared PROPERTIES DEFINE_SYMBOL PNG_BUILD_DLL)
   endif()
-  target_link_libraries(png_shared ${ZLIB_LIBRARIES} ${M_LIBRARY})
+  target_include_directories(png_shared
+                             PUBLIC
+                               $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/libpng${PNGLIB_ABI_VERSION}>
+                               $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
+                             PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
+  target_link_libraries(png_shared PRIVATE ZLIB::ZLIB ${M_LIBRARY})
 endif()
 
 if(PNG_STATIC)
@@ -679,7 +682,12 @@ if(PNG_STATIC)
   set_target_properties(png_static PROPERTIES
                         OUTPUT_NAME "${PNG_STATIC_OUTPUT_NAME}"
                         DEBUG_POSTFIX "${PNG_DEBUG_POSTFIX}")
-  target_link_libraries(png_static ${ZLIB_LIBRARIES} ${M_LIBRARY})
+  target_include_directories(png_static
+                             PUBLIC
+                               $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/libpng${PNGLIB_ABI_VERSION}>
+                               $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
+                             PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
+  target_link_libraries(png_static PRIVATE ZLIB::ZLIB ${M_LIBRARY})
 endif()
 
 if(PNG_FRAMEWORK)
@@ -695,6 +703,11 @@ if(PNG_FRAMEWORK)
                         XCODE_ATTRIBUTE_INSTALL_PATH "@rpath"
                         PUBLIC_HEADER "${libpng_public_hdrs}"
                         OUTPUT_NAME "png")
+  target_include_directories(png_framework
+                             PUBLIC
+                               $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/libpng${PNGLIB_ABI_VERSION}>
+                               $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
+                             PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
   target_link_libraries(png_framework ${ZLIB_LIBRARIES} ${M_LIBRARY})
 endif()
 
@@ -900,7 +913,7 @@ if(PNG_SHARED AND PNG_TOOLS)
   set(PNG_BIN_TARGETS pngfix)
 
   add_executable(png-fix-itxt ${png_fix_itxt_sources})
-  target_link_libraries(png-fix-itxt PRIVATE ${ZLIB_LIBRARIES} ${M_LIBRARY})
+  target_link_libraries(png-fix-itxt PRIVATE ZLIB::ZLIB ${M_LIBRARY})
   list(APPEND PNG_BIN_TARGETS png-fix-itxt)
 endif()