Do not use the embedded libloadpng.

Add the option to use a shared libloadpng library.
Patch by Tobias Hansen <[email protected]>

CMakeLists.txt

@@ -35,6 +35,7 @@ option(USE_SHARED_GIFLIB  "Use your installed copy of giflib" off)
 option(USE_SHARED_JPEGLIB "Use your installed copy of jpeglib" off)
 option(USE_SHARED_ZLIB    "Use your installed copy of zlib" off)
 option(USE_SHARED_LIBPNG  "Use your installed copy of libpng" off)
+option(USE_SHARED_LIBLOADPNG "Use your installed copy of libloadpng" off)
 option(USE_SHARED_TINYXML "Use your installed copy of tinyxml" off)
 option(USE_SHARED_GTEST   "Use your installed copy of gtest" off)
 option(USE_SHARED_ALLEGRO4 "Use shared Allegro 4 library (without resize support)" off)

src/CMakeLists.txt

@@ -15,8 +15,6 @@ set(aseprite_libraries aseprite-library undo-lib filters-lib ui-lib gfx-lib base
 include_directories(. .. ../third_party)
 
 # Third-party libraries
-set(libs3rdparty loadpng)
-include_directories(${LOADPNG_DIR})
 
 if(USE_SHARED_JPEGLIB)
   find_package(JPEG)
@@ -73,6 +71,17 @@ else()
   include_directories(${TINYXML_DIR})
 endif()
 
+if(USE_SHARED_LIBLOADPNG)
+  find_library(LIBLOADPNG_LIBRARY NAMES loadpng)
+  find_path(LIBLOADPNG_INCLUDE_DIR NAMES loadpng.h)
+
+  set(libs3rdparty ${libs3rdparty} ${LIBLOADPNG_LIBRARY})
+  include_directories(${LIBLOADPNG_INCLUDE_DIR})
+else()
+  set(libs3rdparty ${libs3rdparty} loadpng)
+  include_directories(${LOADPNG_DIR})
+endif()
+
 if (CMAKE_USE_PTHREADS_INIT)
   set(sys_libs ${sys_libs} ${CMAKE_THREAD_LIBS_INIT})
 endif()

third_party/CMakeLists.txt

@@ -36,4 +36,6 @@ if(ENABLE_UPDATER AND NOT USE_SHARED_CURL)
   add_subdirectory(curl)
 endif()
 
-add_subdirectory(loadpng)
+if(NOT USE_SHARED_LIBLOADPNG)
+ add_subdirectory(loadpng)
+endif()