build: Add a CMake config file compatible with the FindPNG module

Co-authored-by: Cosmin Truta <ctruta@gmail.com>
Signed-off-by: Cosmin Truta <ctruta@gmail.com>

CMakeLists.txt

@@ -1129,6 +1129,30 @@ if(NOT SKIP_INSTALL_EXPORT AND NOT SKIP_INSTALL_ALL)
           FILE libpng${PNGLIB_ABI_VERSION}.cmake)
 endif()
 
+# Create a CMake Config File that can be used via find_package(PNG CONFIG)
+if(NOT SKIP_INSTALL_CONFIG_FILE AND NOT SKIP_INSTALL_ALL)
+  install(TARGETS ${PNG_LIBRARY_TARGETS}
+          EXPORT PNGTargets
+          RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
+          LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
+          ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
+          FRAMEWORK DESTINATION ${CMAKE_INSTALL_LIBDIR})
+
+  include(CMakePackageConfigHelpers)
+  write_basic_package_version_file(PNGConfigVersion.cmake
+                                   VERSION ${PNGLIB_VERSION}
+                                   COMPATIBILITY SameMinorVersion)
+
+  install(EXPORT PNGTargets
+          FILE PNGTargets.cmake
+          NAMESPACE PNG::
+          DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/PNG)
+
+  install(FILES ${CMAKE_CURRENT_SOURCE_DIR}/scripts/cmake/PNGConfig.cmake
+                ${CMAKE_CURRENT_BINARY_DIR}/PNGConfigVersion.cmake
+          DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/PNG)
+endif()
+
 # TODO: Create MSVC import lib for MinGW-compiled shared lib.
 # pexports libpng.dll > libpng.def
 # lib /def:libpng.def /machine:x86

scripts/cmake/PNGConfig.cmake

@@ -0,0 +1,15 @@
+include(CMakeFindDependencyMacro)
+
+find_dependency(ZLIB REQUIRED)
+
+include("${CMAKE_CURRENT_LIST_DIR}/PNGTargets.cmake")
+
+if(NOT TARGET PNG::PNG)
+  if(TARGET PNG::png_shared)
+    add_library(PNG::PNG INTERFACE IMPORTED)
+    target_link_libraries(PNG::PNG INTERFACE PNG::png_shared)
+  elseif(TARGET PNG::png_static)
+    add_library(PNG::PNG INTERFACE IMPORTED)
+    target_link_libraries(PNG::PNG INTERFACE PNG::png_static)
+  endif()
+endif()

scripts/cmake/README.md

@@ -20,6 +20,7 @@ File List
     CMakeLists.txt                 ==>  The main CMake lists file
     scripts/cmake/AUTHORS.md       ==>  The Authors file
     scripts/cmake/README.md        ==>  This file
+    scripts/cmake/PNGConfig.cmake  ==>  Config file for FindPNG
     scripts/cmake/genchk.cmake.in  ==>  Template for genchk.cmake
     scripts/cmake/genout.cmake.in  ==>  Template for genout.cmake
     scripts/cmake/gensrc.cmake.in  ==>  Template for gensrc.cmake