FindPNG: Create an imported PNG::PNG target (#15911)

Imported targets are now the recommended way of dealing with external
library dependencies.  Add one for FindPNG and update documentation
accordingly.  Also add a test case activated by CMake_TEST_FindPNG.

1 files changed, 43 insertions, 7 deletions

diff --git a/Modules/FindPNG.cmake b/Modules/FindPNG.cmake
index 7cf3f22..cae41ac 100644
--- a/Modules/FindPNG.cmake
+++ b/Modules/FindPNG.cmake
@@ -2,13 +2,20 @@
 # FindPNG
 # -------
 #
-# Find the native PNG includes and library
+# Find libpng, the official reference library for the PNG image format.
 #
+# Imported targets
+# ^^^^^^^^^^^^^^^^
 #
+# This module defines the following :prop_tgt:`IMPORTED` target:
 #
-# This module searches libpng, the library for working with PNG images.
+# ``PNG::PNG``
+#   The libpng library, if found.
 #
-# It defines the following variables
+# Result variables
+# ^^^^^^^^^^^^^^^^
+#
+# This module will set the following variables in your project:
 #
 # ``PNG_INCLUDE_DIRS``
 #   where to find png.h, etc.
@@ -22,19 +29,22 @@
 # ``PNG_VERSION_STRING``
 #   the version of the PNG library found (since CMake 2.8.8)
 #
-# Also defined, but not for general use are
+# Obsolete variables
+# ^^^^^^^^^^^^^^^^^^
+#
+# The following variables may also be set, for backwards compatibility:
 #
 # ``PNG_LIBRARY``
 #   where to find the PNG library.
-#
-# For backward compatiblity the variable PNG_INCLUDE_DIR is also set.
-# It has the same value as PNG_INCLUDE_DIRS.
+# ``PNG_INCLUDE_DIR``
+#   where to find the PNG headers (same as PNG_INCLUDE_DIRS)
 #
 # Since PNG depends on the ZLib compression library, none of the above
 # will be defined unless ZLib can be found.
 
 #=============================================================================
 # Copyright 2002-2009 Kitware, Inc.
+# Copyright 2016 Raumfeld
 #
 # Distributed under the OSI-approved BSD License (the "License");
 # see accompanying file Copyright.txt for details.
@@ -105,6 +115,32 @@ if(ZLIB_FOUND)
         endif()
       endif ()
 
+      if(NOT TARGET PNG::PNG)
+        add_library(PNG::PNG UNKNOWN IMPORTED)
+        set_target_properties(PNG::PNG PROPERTIES
+          INTERFACE_COMPILE_DEFINITIONS "${PNG_DEFINITIONS}"
+          INTERFACE_INCLUDE_DIRECTORIES "${PNG_INCLUDE_DIRS}"
+          INTERFACE_LINK_LIBRARIES ZLIB::ZLIB)
+        if(EXISTS "${PNG_LIBRARY}")
+          set_target_properties(PNG::PNG PROPERTIES
+            IMPORTED_LINK_INTERFACE_LANGUAGES "C"
+            IMPORTED_LOCATION "${PNG_LIBRARY}")
+        endif()
+        if(EXISTS "${PNG_LIBRARY_DEBUG}")
+          set_property(TARGET PNG::PNG APPEND PROPERTY
+            IMPORTED_CONFIGURATIONS DEBUG)
+          set_target_properties(PNG::PNG PROPERTIES
+            IMPORTED_LINK_INTERFACE_LANGUAGES_DEBUG "C"
+            IMPORTED_LOCATION_DEBUG "${PNG_LIBRARY_DEBUG}")
+        endif()
+        if(EXISTS "${PNG_LIBRARY_RELEASE}")
+          set_property(TARGET PNG::PNG APPEND PROPERTY
+            IMPORTED_CONFIGURATIONS RELEASE)
+          set_target_properties(PNG::PNG PROPERTIES
+            IMPORTED_LINK_INTERFACE_LANGUAGES_RELEASE "C"
+            IMPORTED_LOCATION_RELEASE "${PNG_LIBRARY_RELEASE}")
+        endif()
+      endif()
   endif ()
 
   if (PNG_PNG_INCLUDE_DIR AND EXISTS "${PNG_PNG_INCLUDE_DIR}/png.h")