commit a484541d4b6203d538f1a65db5a95e98f5bde920
Author:     Albrecht Schlosser <albrechts.fltk@online.de>
AuthorDate: Fri Apr 30 19:47:47 2021 +0200
Commit:     Albrecht Schlosser <albrechts.fltk@online.de>
CommitDate: Fri Apr 30 19:47:47 2021 +0200

    CMake: improve detection and configuration of image libs
    
    Also: fix old (pre 3.13) link_directories() usage

 CMake/fl_create_example.cmake |  4 +--
 CMake/options.cmake           | 84 ++++++++++++++++++++++++-------------------
 fluid/CMakeLists.txt          |  4 +--
 jpeg/CMakeLists.txt           | 51 ++++++++++++++++++--------
 png/CMakeLists.txt            | 39 ++++++++++----------
 zlib/CMakeLists.txt           | 18 ++++++++++
 6 files changed, 126 insertions(+), 74 deletions(-)

diff --git CMake/fl_create_example.cmake CMake/fl_create_example.cmake
index a245bb5..8071b50 100644
--- CMake/fl_create_example.cmake
+++ CMake/fl_create_example.cmake
@@ -117,9 +117,9 @@ macro (CREATE_EXAMPLE NAME SOURCES LIBRARIES)
 
   if (FLTK_HAVE_CAIRO)
     if (CMAKE_VERSION VERSION_LESS "3.13")
-      link_directories (${TARGET_NAME} PUBLIC ${PKG_CAIRO_LIBRARY_DIRS})
+      link_directories    (${PKG_CAIRO_LIBRARY_DIRS})
     else()
-      target_link_directories (${TARGET_NAME} PUBLIC ${PKG_CAIRO_LIBRARY_DIRS})
+      target_link_directories (${TARGET_NAME} PRIVATE ${PKG_CAIRO_LIBRARY_DIRS})
     endif()
   endif (FLTK_HAVE_CAIRO)
 
diff --git CMake/options.cmake CMake/options.cmake
index 008088a..cf50da6 100644
--- CMake/options.cmake
+++ CMake/options.cmake
@@ -168,11 +168,16 @@ if (OPTION_CAIRO OR OPTION_CAIROEXT)
     endif (OPTION_CAIROEXT)
     add_subdirectory (cairo)
 
-    # fl_debug_var (PKG_CAIRO_INCLUDE_DIRS)
-    # fl_debug_var (PKG_CAIRO_CFLAGS)
-    # fl_debug_var (PKG_CAIRO_STATIC_CFLAGS)
-    # fl_debug_var (PKG_CAIRO_LIBRARIES)
-    # fl_debug_var (PKG_CAIRO_STATIC_LIBRARIES)
+    if (0)
+      fl_debug_var (PKG_CAIRO_INCLUDE_DIRS)
+      fl_debug_var (PKG_CAIRO_CFLAGS)
+      fl_debug_var (PKG_CAIRO_LIBRARIES)
+      fl_debug_var (PKG_CAIRO_LIBRARY_DIRS)
+      fl_debug_var (PKG_CAIRO_STATIC_INCLUDE_DIRS)
+      fl_debug_var (PKG_CAIRO_STATIC_CFLAGS)
+      fl_debug_var (PKG_CAIRO_STATIC_LIBRARIES)
+      fl_debug_var (PKG_CAIRO_STATIC_LIBRARY_DIRS)
+    endif()
 
     include_directories (${PKG_CAIRO_INCLUDE_DIRS})
 
@@ -339,87 +344,92 @@ endif (debug_threads)
 unset (debug_threads)
 
 #######################################################################
-option (OPTION_USE_SYSTEM_ZLIB "use system zlib" ON)
+#  Image Library Options
+#######################################################################
+
+option (OPTION_USE_SYSTEM_ZLIB      "use system zlib"    ON)
+
+if (APPLE)
+  option (OPTION_USE_SYSTEM_LIBJPEG "use system libjpeg" OFF)
+  option (OPTION_USE_SYSTEM_LIBPNG  "use system libpng"  OFF)
+else ()
+  option (OPTION_USE_SYSTEM_LIBJPEG "use system libjpeg" ON)
+  option (OPTION_USE_SYSTEM_LIBPNG  "use system libpng"  ON)
+endif ()
+
+#######################################################################
+#  Image Library : ZLIB
+#######################################################################
 
 if (OPTION_USE_SYSTEM_ZLIB)
-  include (FindZLIB)
-endif (OPTION_USE_SYSTEM_ZLIB)
+  find_package (ZLIB)
+endif ()
 
-if (ZLIB_FOUND)
+if (OPTION_USE_SYSTEM_ZLIB AND ZLIB_FOUND)
+  set (FLTK_USE_BUILTIN_ZLIB FALSE)
   set (FLTK_ZLIB_LIBRARIES ${ZLIB_LIBRARIES})
   include_directories (${ZLIB_INCLUDE_DIRS})
-  set (FLTK_BUILTIN_ZLIB_FOUND FALSE)
 else()
   if (OPTION_USE_SYSTEM_ZLIB)
     message (STATUS "cannot find system zlib library - using built-in\n")
-  endif (OPTION_USE_SYSTEM_ZLIB)
+  endif ()
 
   add_subdirectory (zlib)
+  set (FLTK_USE_BUILTIN_ZLIB TRUE)
   set (FLTK_ZLIB_LIBRARIES fltk_z)
   set (ZLIB_INCLUDE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/zlib)
   include_directories (${CMAKE_CURRENT_SOURCE_DIR}/zlib)
-  set (FLTK_BUILTIN_ZLIB_FOUND TRUE)
-endif (ZLIB_FOUND)
+endif ()
 
 set (HAVE_LIBZ 1)
 
 #######################################################################
-if (APPLE)
-  option (OPTION_USE_SYSTEM_LIBJPEG "use system libjpeg" OFF)
-else ()
-  option (OPTION_USE_SYSTEM_LIBJPEG "use system libjpeg" ON)
-endif (APPLE)
 
 if (OPTION_USE_SYSTEM_LIBJPEG)
-  include (FindJPEG)
-endif (OPTION_USE_SYSTEM_LIBJPEG)
+  find_package (JPEG)
+endif ()
 
-if (JPEG_FOUND)
+if (OPTION_USE_SYSTEM_LIBJPEG AND JPEG_FOUND)
+  set (FLTK_USE_BUILTIN_JPEG FALSE)
   set (FLTK_JPEG_LIBRARIES ${JPEG_LIBRARIES})
   include_directories (${JPEG_INCLUDE_DIR})
-  set (FLTK_BUILTIN_JPEG_FOUND FALSE)
 else ()
   if (OPTION_USE_SYSTEM_LIBJPEG)
     message (STATUS "cannot find system jpeg library - using built-in\n")
-  endif (OPTION_USE_SYSTEM_LIBJPEG)
+  endif ()
 
   add_subdirectory (jpeg)
+  set (FLTK_USE_BUILTIN_JPEG TRUE)
   set (FLTK_JPEG_LIBRARIES fltk_jpeg)
   include_directories (${CMAKE_CURRENT_SOURCE_DIR}/jpeg)
-  set (FLTK_BUILTIN_JPEG_FOUND TRUE)
-endif (JPEG_FOUND)
+endif ()
 
 set (HAVE_LIBJPEG 1)
 
 #######################################################################
-if (APPLE)
-  option (OPTION_USE_SYSTEM_LIBPNG "use system libpng" OFF)
-else ()
-  option (OPTION_USE_SYSTEM_LIBPNG "use system libpng" ON)
-endif (APPLE)
 
 if (OPTION_USE_SYSTEM_LIBPNG)
-  include (FindPNG)
-endif (OPTION_USE_SYSTEM_LIBPNG)
+  find_package (PNG)
+endif ()
 
-if (PNG_FOUND)
+if (OPTION_USE_SYSTEM_LIBPNG AND PNG_FOUND)
+  set (FLTK_USE_BUILTIN_PNG FALSE)
   set (FLTK_PNG_LIBRARIES ${PNG_LIBRARIES})
   include_directories (${PNG_INCLUDE_DIR})
   add_definitions (${PNG_DEFINITIONS})
-  set (FLTK_BUILTIN_PNG_FOUND FALSE)
 else()
   if (OPTION_USE_SYSTEM_LIBPNG)
     message (STATUS "cannot find system png library - using built-in\n")
-  endif (OPTION_USE_SYSTEM_LIBPNG)
+  endif ()
 
   add_subdirectory (png)
+  set (FLTK_USE_BUILTIN_PNG TRUE)
   set (FLTK_PNG_LIBRARIES fltk_png)
   set (HAVE_PNG_H 1)
   set (HAVE_PNG_GET_VALID 1)
   set (HAVE_PNG_SET_TRNS_TO_ALPHA 1)
   include_directories (${CMAKE_CURRENT_SOURCE_DIR}/png)
-  set (FLTK_BUILTIN_PNG_FOUND TRUE)
-endif (PNG_FOUND)
+endif ()
 
 set (HAVE_LIBPNG 1)
 
diff --git fluid/CMakeLists.txt fluid/CMakeLists.txt
index 1b98c17..73cdb45 100644
--- fluid/CMakeLists.txt
+++ fluid/CMakeLists.txt
@@ -72,9 +72,9 @@ endif (APPLE AND (NOT OPTION_APPLE_X11) AND (NOT OPTION_APPLE_SDL))
 target_link_libraries (fluid fltk fltk_images fltk_forms)
 if (FLTK_HAVE_CAIRO)
   if (CMAKE_VERSION VERSION_LESS "3.13")
-    link_directories (fluid PUBLIC ${PKG_CAIRO_LIBRARY_DIRS})
+    link_directories (${PKG_CAIRO_LIBRARY_DIRS})
   else()
-    target_link_directories (fluid PUBLIC ${PKG_CAIRO_LIBRARY_DIRS})
+    target_link_directories (fluid PRIVATE ${PKG_CAIRO_LIBRARY_DIRS})
   endif()
 endif (FLTK_HAVE_CAIRO)
 
diff --git jpeg/CMakeLists.txt jpeg/CMakeLists.txt
index 2e30f2d..16a423a 100644
--- jpeg/CMakeLists.txt
+++ jpeg/CMakeLists.txt
@@ -1,36 +1,56 @@
+#
+# JPEG library CMake configuration for the Fast Light Toolkit (FLTK).
+#
+# Copyright 1998-2021 by Bill Spitzak and others.
+#
+# This library is free software. Distribution and use rights are outlined in
+# the file "COPYING" which should have been included with this file.  If this
+# file is missing or damaged, see the license at:
+#
+#     https://www.fltk.org/COPYING.php
+#
+# Please see the following page on how to report bugs and issues:
+#
+#     https://www.fltk.org/bugs.php
+#
 
 # memmgr back ends: compile only one of these into a working library
 # (For now, let's use the mode that requires the image fit into memory.
 # This is the recommended mode for Win32 anyway.)
-set(systemdependent_SRCS jmemnobs.c)
+
+set (systemdependent_SRCS jmemnobs.c)
 
 # library object files common to compression and decompression
-set(common_SRCS
-   jaricom.c jcomapi.c jutils.c jerror.c jmemmgr.c
+
+set (common_SRCS
+     jaricom.c jcomapi.c jutils.c jerror.c jmemmgr.c
 )
 
 # compression library object files
-set(compression_SRCS
-   jcapimin.c jcapistd.c jcarith.c jctrans.c jcparam.c jdatadst.c jcinit.c
-   jcmaster.c jcmarker.c jcmainct.c jcprepct.c jccoefct.c jccolor.c
-   jcsample.c jchuff.c jcdctmgr.c jfdctfst.c jfdctflt.c
-   jfdctint.c
+
+set (compression_SRCS
+     jcapimin.c jcapistd.c jcarith.c jctrans.c jcparam.c jdatadst.c jcinit.c
+     jcmaster.c jcmarker.c jcmainct.c jcprepct.c jccoefct.c jccolor.c
+     jcsample.c jchuff.c jcdctmgr.c jfdctfst.c jfdctflt.c
+     jfdctint.c
 )
 
 # decompression library object files
-set(decompression_SRCS
-   jdapimin.c jdapistd.c jdarith.c jdtrans.c jdatasrc.c jdmaster.c
-   jdinput.c jdmarker.c jdhuff.c jdmainct.c jdcoefct.c
-   jdpostct.c jddctmgr.c jidctfst.c jidctflt.c jidctint.c
-   jdsample.c jdcolor.c jquant1.c jquant2.c jdmerge.c
+
+set (decompression_SRCS
+     jdapimin.c jdapistd.c jdarith.c jdtrans.c jdatasrc.c jdmaster.c
+     jdinput.c jdmarker.c jdhuff.c jdmainct.c jdcoefct.c
+     jdpostct.c jddctmgr.c jidctfst.c jidctflt.c jidctint.c
+     jdsample.c jdcolor.c jquant1.c jquant2.c jdmerge.c
 )
 
-list(APPEND BUILD_SRCS "${systemdependent_SRCS};${common_SRCS}")
-list(APPEND BUILD_SRCS "${compression_SRCS};${decompression_SRCS}")
+list (APPEND BUILD_SRCS "${systemdependent_SRCS};${common_SRCS}")
+list (APPEND BUILD_SRCS "${compression_SRCS};${decompression_SRCS}")
 
 #######################################################################
 
 # Suppress some Visual Studio compiler warnings
+
 set (msvc_warnings /wd4267)
 
 #######################################################################
@@ -48,6 +68,7 @@ endif (MSVC)
 #######################################################################
 
 if (OPTION_BUILD_SHARED_LIBS)
+
   FL_ADD_LIBRARY (fltk_jpeg SHARED "${BUILD_SRCS}")
 
   if (MSVC)
diff --git png/CMakeLists.txt png/CMakeLists.txt
index faf7062..a67c7eb 100644
--- png/CMakeLists.txt
+++ png/CMakeLists.txt
@@ -39,29 +39,32 @@ set(PNG_SRCS
 )
 
 #######################################################################
-FL_ADD_LIBRARY(fltk_png STATIC "${PNG_SRCS}")
-# install the png headers
-install(FILES png.h;pngconf.h;pnglibconf.h
-    DESTINATION ${FLTK_INCLUDEDIR}/FL/images
-)
+# Build the static library
+#######################################################################
 
-if(OPTION_USE_SYSTEM_ZLIB)
-    target_link_libraries(fltk_png ${FLTK_ZLIB_LIBRARIES})
-else()
-    target_link_libraries(fltk_png fltk_z)
-endif(OPTION_USE_SYSTEM_ZLIB)
+FL_ADD_LIBRARY (fltk_png STATIC "${PNG_SRCS}")
+target_link_libraries (fltk_png ${FLTK_ZLIB_LIBRARIES})
 
 #######################################################################
-if(OPTION_BUILD_SHARED_LIBS)
+# Build the shared library (optional)
 #######################################################################
-FL_ADD_LIBRARY(fltk_png SHARED "${PNG_SRCS}")
 
-if(OPTION_USE_SYSTEM_ZLIB)
-    target_link_libraries(fltk_png_SHARED ${FLTK_ZLIB_LIBRARIES})
-else()
-    target_link_libraries(fltk_png_SHARED fltk_z_SHARED)
-endif(OPTION_USE_SYSTEM_ZLIB)
+if (OPTION_BUILD_SHARED_LIBS)
+
+  FL_ADD_LIBRARY (fltk_png SHARED "${PNG_SRCS}")
+
+  if (FLTK_USE_BUILTIN_ZLIB)
+    target_link_libraries (fltk_png_SHARED fltk_z_SHARED)
+  else()
+    target_link_libraries (fltk_png_SHARED ${FLTK_ZLIB_LIBRARIES})
+  endif ()
+
+endif ()
 
 #######################################################################
-endif(OPTION_BUILD_SHARED_LIBS)
+# Install the library headers
 #######################################################################
+
+install (FILES png.h pngconf.h pnglibconf.h
+         DESTINATION ${FLTK_INCLUDEDIR}/FL/images
+)
diff --git zlib/CMakeLists.txt zlib/CMakeLists.txt
index 33d6f58..1dc3042 100644
--- zlib/CMakeLists.txt
+++ zlib/CMakeLists.txt
@@ -1,5 +1,21 @@
+#
+# ZLIB library CMake configuration for the Fast Light Toolkit (FLTK).
+#
+# Copyright 1998-2021 by Bill Spitzak and others.
+#
+# This library is free software. Distribution and use rights are outlined in
+# the file "COPYING" which should have been included with this file.  If this
+# file is missing or damaged, see the license at:
+#
+#     https://www.fltk.org/COPYING.php
+#
+# Please see the following page on how to report bugs and issues:
+#
+#     https://www.fltk.org/bugs.php
+#
 
 # source files for zlib
+
 set (ZLIB_SRCS
       adler32.c
       compress.c
@@ -21,6 +37,7 @@ set (ZLIB_SRCS
 #######################################################################
 
 # Suppress some Visual Studio compiler warnings
+
 set (msvc_warnings /wd4267 /wd4996)
 
 #######################################################################
@@ -38,6 +55,7 @@ endif (MSVC)
 #######################################################################
 
 if (OPTION_BUILD_SHARED_LIBS)
+
   FL_ADD_LIBRARY (fltk_z SHARED "${ZLIB_SRCS}")
 
   if (MSVC)