Minor updates of bundled libraries and README.CMake.txt

Update Makefiles, CMakeLists.txt, improve formatting.

2 files changed, 18 insertions, 16 deletions

diff --git a/png/CMakeLists.txt b/png/CMakeLists.txt
index b47323fe4..c61b1a544 100644
--- a/png/CMakeLists.txt
+++ b/png/CMakeLists.txt
@@ -1,7 +1,7 @@
 #
 # PNG library CMake configuration for the Fast Light Toolkit (FLTK).
 #
-# Copyright 1998-2022 by Bill Spitzak and others.
+# Copyright 1998-2023 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
@@ -15,7 +15,7 @@
 #
 
 # source files for png
-set(PNG_SRCS
+set (PNG_SRCS
   png.c
   pngerror.c
   pngget.c
@@ -34,6 +34,13 @@ set(PNG_SRCS
 )
 
 #######################################################################
+# Note: This file is used only if we build the bundled PNG library,
+#  and if we do this we MUST also build and use the *bundled* ZLIB,
+#  hence we MUST also link against the bundled ZLIB (see below).
+#  There's no need to check which ZLIB version to use in this context.
+#######################################################################
+
+#######################################################################
 # Build some files on ARM (e.g. Apple M1 systems)
 #######################################################################
 
@@ -43,16 +50,16 @@ set(PNG_SRCS
 # This includes all non-macOS platforms.
 
 if (CMAKE_OSX_ARCHITECTURES)
-  string(REGEX MATCH "arm64" is_arm "${CMAKE_OSX_ARCHITECTURES}")
+  string (REGEX MATCH "arm64" is_arm "${CMAKE_OSX_ARCHITECTURES}")
 else ()
   set (is_arm TRUE)
 endif ()
 
 if (is_arm)
   LIST (APPEND PNG_SRCS
-    arm/arm_init.c
-    arm/filter_neon_intrinsics.c
-    arm/palette_neon_intrinsics.c
+        arm/arm_init.c
+        arm/filter_neon_intrinsics.c
+        arm/palette_neon_intrinsics.c
   )
 endif ()
 
@@ -65,8 +72,8 @@ unset (is_arm)
 #######################################################################
 
 LIST (APPEND PNG_SRCS
-  powerpc/powerpc_init.c
-  powerpc/filter_vsx_intrinsics.c
+      powerpc/powerpc_init.c
+      powerpc/filter_vsx_intrinsics.c
 )
 
 #######################################################################
@@ -74,7 +81,7 @@ LIST (APPEND PNG_SRCS
 #######################################################################
 
 FL_ADD_LIBRARY (fltk_png STATIC "${PNG_SRCS}")
-target_link_libraries (fltk_png ${FLTK_ZLIB_LIBRARIES})
+target_link_libraries (fltk_png PUBLIC fltk_z)
 
 #######################################################################
 # Build the shared library (optional)
@@ -83,12 +90,7 @@ target_link_libraries (fltk_png ${FLTK_ZLIB_LIBRARIES})
 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)
-  else()
-    target_link_libraries (fltk_png_SHARED ${FLTK_ZLIB_LIBRARIES})
-  endif ()
+  target_link_libraries (fltk_png_SHARED PUBLIC fltk_z_SHARED)
 
 endif ()
 
diff --git a/png/Makefile b/png/Makefile
index 3326f7a8c..7fd9a8765 100644
--- a/png/Makefile
+++ b/png/Makefile
@@ -2,7 +2,7 @@
 # PNG library Makefile for the Fast Light Toolkit (FLTK).
 #
 # Copyright 1997-2011 by Easy Software Products.
-# Copyright 2012-2020 by Bill Spitzak and others.
+# Copyright 2012-2023 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