Require PNG++ for building.

cmake/modules/Findpng++.cmake

@@ -0,0 +1,61 @@
+# - Try to find png++
+#
+# The following variables are optionally searched for defaults
+#  png++_ROOT_DIR:            Base directory where all png++ components are found
+#
+# The following are set after configuration is done:
+#  png++_FOUND
+#  png++_INCLUDE_DIRS
+#  png++_LIBRARIES
+
+find_package(PNG REQUIRED)
+
+include(FindPackageHandleStandardArgs)
+
+set(png++_ROOT_DIR "" CACHE PATH "Folder contains png++")
+
+find_path(png++_INCLUDE_DIR
+    NAMES
+        png++/color.hpp
+        png++/config.hpp
+        png++/consumer.hpp
+        png++/convert_color_space.hpp
+        png++/end_info.hpp
+        png++/error.hpp
+        png++/ga_pixel.hpp
+        png++/generator.hpp
+        png++/gray_pixel.hpp
+        png++/image.hpp
+        png++/image_info.hpp
+        png++/index_pixel.hpp
+        png++/info.hpp
+        png++/info_base.hpp
+        png++/io_base.hpp
+        png++/packed_pixel.hpp
+        png++/palette.hpp
+        png++/pixel_buffer.hpp
+        png++/pixel_traits.hpp
+        png++/png.hpp
+        png++/reader.hpp
+        png++/require_color_space.hpp
+        png++/rgb_pixel.hpp
+        png++/rgba_pixel.hpp
+        png++/streaming_base.hpp
+        png++/tRNS.hpp
+        png++/types.hpp
+        png++/writer.hpp
+    PATHS
+        ${png++_ROOT_DIR}
+    PATH_SUFFIXES
+        src)
+
+set(png++_INCLUDE_DIRS ${png++_INCLUDE_DIR} ${PNG_INCLUDE_DIRS})
+set(png++_LIBRARIES ${PNG_LIBRARIES})
+
+find_package_handle_standard_args(png++ DEFAULT_MSG
+    png++_INCLUDE_DIR)
+
+if(png++_FOUND)
+    set(png++_INCLUDE_DIRS ${png++_INCLUDE_DIR})
+    set(png++_LIBRARIES ${png++_LIBRARY})
+endif()