CMake: refactor and reformat CMake files

- raise minimum CMake version from 2.6.3 to 3.2.3 (Jun 01, 2015)
- indent all CMake files according to the CMP (2 col.)
- refactor FLTK version number definitions and usage
- unify CMake and autoconf/configure variable names:
  - FL_VERSION -> FLTK_VERSION
  - FL_MAJOR_VERSION -> FLTK_VERSION_MAJOR
  - etc. for _MINOR_ and _PATCH_, respectively
  - note: this does not affect FL_VERSION etc. in source code
- generate "export headers" for all libraries (experimental: OFF)
- port some forgotten goodies from branch-1.3 to master
- merge and improve macro 'create_example' (WIP)
- remove "temporary" options and code for older CMake versions
- include and use 'GenerateExportHeader' (experimental, WIP: OFF)
  - note: created header files are not yet used
- build only *one* DLL with Visual Studio (tested, works)
  - similar to the bundled IDE projects in 1.3.x
- add some dynamically linked test/demo programs ('*-shared')
  if shared libraries are built (WIP)
- split 'macros.cmake': use one file per macro

1 files changed, 103 insertions, 37 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 172a949d0..281d6b440 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -2,7 +2,7 @@
 # Main CMakeLists.txt to build the FLTK project using CMake (www.cmake.org)
 # Written by Michael Surette
 #
-# Copyright 1998-2018 by Bill Spitzak and others.
+# Copyright 1998-2020 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
@@ -15,64 +15,87 @@
 #     https://www.fltk.org/bugs.php
 #
 
-# Prevent annoying warning under Cygwin; this must be before project().
-# Remove when CMake >= 2.8.4 is required
-set(CMAKE_LEGACY_CYGWIN_WIN32 0)
+#######################################################################
+# set CMake minimum version (must be before `project()`
+#######################################################################
+
+# Note: previous (1.3.x) minimum version
+# cmake_minimum_required (VERSION 2.6.3)
+
+# Note: minimum CMake version required by GNUInstallDirs
+# cmake_minimum_required (VERSION 2.8.4)
+
+# Minimum CMake version required by FLTK 1.4 (06/2020, work in progress)
+cmake_minimum_required (VERSION 3.2.3 FATAL_ERROR)
+
+#######################################################################
+# define the FLTK project and version
+#######################################################################
 
-project(FLTK)
-cmake_minimum_required(VERSION 2.6.3)
+project (FLTK VERSION 1.4.0)
 
 #######################################################################
-# define some macros
+# include macro definitions of generally used macros
 #######################################################################
-include(CMake/macros.cmake)
+
+include (CMake/fl_debug_var.cmake)
+include (CMake/fl_add_library.cmake)
+
+if (false)
+  fl_debug_var (FLTK_VERSION_MAJOR)
+  fl_debug_var (FLTK_VERSION_MINOR)
+  fl_debug_var (FLTK_VERSION_PATCH)
+  fl_debug_var (FLTK_VERSION)
+  fl_debug_var (FLTK_VERSION)
+endif (false)
 
 #######################################################################
 # basic setup
 #######################################################################
-include(CMake/setup.cmake)
+include (CMake/setup.cmake)
 
 #######################################################################
 # check for headers, libraries and functions
 #######################################################################
-include(CMake/resources.cmake)
+include (CMake/resources.cmake)
 
 #######################################################################
 # options
 #######################################################################
-include(CMake/options.cmake)
+include (CMake/options.cmake)
 
 #######################################################################
 # Android Studio setup
 #######################################################################
 if (OPTION_CREATE_ANDROID_STUDIO_IDE)
-  include(CMake/android.cmake)
+  include (CMake/android.cmake)
 endif (OPTION_CREATE_ANDROID_STUDIO_IDE)
 
-
 #######################################################################
 # print (debug) several build variables and options
 #######################################################################
 
 set (debug_build 0) # set to 1 to show debug info
+
 if (debug_build)
   message ("")
   message (STATUS "${CMAKE_CURRENT_LIST_DIR}/CMakeLists.txt: set debug_build to 0 to disable the following info:")
-  fl_debug_var(WIN32)
-  fl_debug_var(MINGW)
-  fl_debug_var(CYGWIN)
-  fl_debug_var(MSVC)
-  fl_debug_var(UNIX)
-  fl_debug_var(APPLE)
-  fl_debug_var(ANDROID)
-  fl_debug_var(CMAKE_BUILD_TYPE)
-  fl_debug_var(CMAKE_SIZEOF_VOID_P)
-  fl_debug_var(OPTION_OPTIM)
-  fl_debug_var(CMAKE_C_FLAGS)
-  fl_debug_var(CMAKE_CXX_FLAGS)
-  fl_debug_var(CMAKE_EXE_LINKER_FLAGS)
+  fl_debug_var (WIN32)
+  fl_debug_var (MINGW)
+  fl_debug_var (CYGWIN)
+  fl_debug_var (MSVC)
+  fl_debug_var (UNIX)
+  fl_debug_var (APPLE)
+  fl_debug_var (ANDROID)
+  fl_debug_var (CMAKE_BUILD_TYPE)
+  fl_debug_var (CMAKE_SIZEOF_VOID_P)
+  fl_debug_var (OPTION_OPTIM)
+  fl_debug_var (CMAKE_C_FLAGS)
+  fl_debug_var (CMAKE_CXX_FLAGS)
+  fl_debug_var (CMAKE_EXE_LINKER_FLAGS)
   message (STATUS "${CMAKE_CURRENT_LIST_DIR}/CMakeLists.txt: end of debug_build info.")
 endif (debug_build)
+
 unset (debug_build)
 
 #######################################################################
@@ -81,25 +104,25 @@ unset (debug_build)
 # install.cmake creates these files for an installed FLTK
 # these two would only differ in paths, so common variables are set here
 #######################################################################
-include(CMake/variables.cmake)
+include (CMake/variables.cmake)
 
 #######################################################################
 # final config and export
 #######################################################################
-include(CMake/export.cmake)
+include (CMake/export.cmake)
 
-configure_file(
- ${CMAKE_CURRENT_SOURCE_DIR}/abi-version.cmake.in
- ${CMAKE_CURRENT_BINARY_DIR}/FL/abi-version.h
- @ONLY
- )
+configure_file (
+  ${CMAKE_CURRENT_SOURCE_DIR}/abi-version.cmake.in
+  ${CMAKE_CURRENT_BINARY_DIR}/FL/abi-version.h
+  @ONLY
+)
 
 #######################################################################
 # build examples - these have to be built after fluid is built/imported
 #######################################################################
-if(OPTION_BUILD_EXAMPLES)
-   add_subdirectory(test)
-endif(OPTION_BUILD_EXAMPLES)
+if (OPTION_BUILD_EXAMPLES)
+   add_subdirectory (test)
+endif (OPTION_BUILD_EXAMPLES)
 
 #######################################################################
 # Android Studio wrapup
@@ -111,4 +134,47 @@ endif (OPTION_CREATE_ANDROID_STUDIO_IDE)
 #######################################################################
 # installation
 #######################################################################
-include(CMake/install.cmake)
+include (CMake/install.cmake)
+
+#######################################################################
+# Generate Library Export Headers          *** EXPERIMENTAL *** WIP ***
+#######################################################################
+
+# Enable (1) or disable (0) generation of experimental headers (WIP)
+set (GENERATE_EXPORT_HEADERS 0)
+
+if (OPTION_BUILD_SHARED_LIBS AND GENERATE_EXPORT_HEADERS)
+
+  include (GenerateExportHeader)
+
+  generate_export_header (fltk_SHARED
+    BASE_NAME fl
+    EXPORT_FILE_NAME FL/fltk_export.h
+    STATIC_DEFINE FL_STATIC_LIB
+  )
+
+  if (NOT MSVC)
+
+    # Visual Studio builds only one shared lib (DLL)
+
+    generate_export_header (fltk_images_SHARED
+      BASE_NAME fl_images
+      EXPORT_FILE_NAME FL/fltk_images_export.h
+      STATIC_DEFINE FL_STATIC_LIB
+    )
+
+    generate_export_header (fltk_forms_SHARED
+      BASE_NAME fl_forms
+      EXPORT_FILE_NAME FL/fltk_forms_export.h
+      STATIC_DEFINE FL_STATIC_LIB
+    )
+
+    generate_export_header (fltk_gl_SHARED
+      BASE_NAME fl_gl
+      EXPORT_FILE_NAME FL/fltk_gl_export.h
+      STATIC_DEFINE FL_STATIC_LIB
+    )
+
+  endif (NOT MSVC)
+
+endif (OPTION_BUILD_SHARED_LIBS AND GENERATE_EXPORT_HEADERS)