Introduce "Modern CMake" in FLTK

This is a big commit and there are too many changes to list them all.
The main changes are:

- rename all CMake build options to 'FLTK_*'
- export library targets with namespace (prefix) 'fltk::'
- standardize shared library target names with suffix '-shared'
- set public build properties on libraries for consumers
- document library names and aliases in README.CMake.txt
- document changes in "Migrating Code from FLTK 1.3 to 1.4"
- partial backwards compatibility for old user projects

Included but not directly related changes:

- fix Windows (Visual Studio) DLL build
- add CMake function fl_debug_target() to show target properties
- don't build test programs if FLTK is a subproject
- internal: reformat CMake code: remove space before '('

Thanks to Matthias and Manolo for their help, testing, and feeback.

1 files changed, 33 insertions, 32 deletions

diff --git a/CMake/install.cmake b/CMake/install.cmake
index ea36ab301..651d8a0f1 100644
--- a/CMake/install.cmake
+++ b/CMake/install.cmake
@@ -2,7 +2,7 @@
 # Installation support for building the FLTK project using CMake (www.cmake.org)
 # Originally written by Michael Surette
 #
-# Copyright 1998-2022 by Bill Spitzak and others.
+# Copyright 1998-2024 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
@@ -25,11 +25,11 @@ configure_file(
   "${CMAKE_CURRENT_BINARY_DIR}/cmake_uninstall.cmake"
   @ONLY
 )
-add_custom_target (uninstall
+add_custom_target(uninstall
   "${CMAKE_COMMAND}" -P "${CMAKE_CURRENT_BINARY_DIR}/cmake_uninstall.cmake"
 )
 
-install (DIRECTORY
+install(DIRECTORY
   ${CMAKE_CURRENT_SOURCE_DIR}/FL
   DESTINATION ${FLTK_INCLUDEDIR} USE_SOURCE_PERMISSIONS
   FILES_MATCHING
@@ -37,28 +37,29 @@ install (DIRECTORY
     PATTERN "fl_config.h" EXCLUDE
 )
 
-install (DIRECTORY
+install(DIRECTORY
   ${CMAKE_CURRENT_BINARY_DIR}/FL
   DESTINATION ${FLTK_INCLUDEDIR} USE_SOURCE_PERMISSIONS
   FILES_MATCHING
     PATTERN "*.[hH]"
 )
 
-if (OPTION_CREATE_LINKS)
-  install (SCRIPT ${CMAKE_CURRENT_BINARY_DIR}/install-symlinks.cmake)
-endif (OPTION_CREATE_LINKS)
+if(FLTK_INSTALL_LINKS)
+  install(SCRIPT ${CMAKE_CURRENT_BINARY_DIR}/install-symlinks.cmake)
+endif(FLTK_INSTALL_LINKS)
 
 # generate FLTKConfig.cmake for installed directory use
-set (INCLUDE_DIRS ${CMAKE_INSTALL_PREFIX}/include)
-if (FLTK_HAVE_CAIRO)
-  list (APPEND INCLUDE_DIRS ${PKG_CAIRO_INCLUDE_DIRS})
-endif ()
+set(INCLUDE_DIRS ${CMAKE_INSTALL_PREFIX}/include)
+if(FLTK_HAVE_CAIRO)
+  list(APPEND INCLUDE_DIRS ${PKG_CAIRO_INCLUDE_DIRS})
+endif()
 
-set (CONFIG_PATH ${CMAKE_INSTALL_PREFIX}/${FLTK_CONFIG_PATH})
+set(CONFIG_PATH ${CMAKE_INSTALL_PREFIX}/${FLTK_CONFIG_PATH})
 
-install (EXPORT FLTK-Targets
+install(EXPORT FLTK-Targets
   DESTINATION ${FLTK_CONFIG_PATH}
   FILE FLTK-Targets.cmake
+  NAMESPACE fltk::
 )
 
 configure_file(
@@ -67,26 +68,26 @@ configure_file(
   @ONLY
 )
 
-install (FILES
+install(FILES
   ${CMAKE_CURRENT_BINARY_DIR}/etc/FLTKConfig.cmake
   DESTINATION ${FLTK_CONFIG_PATH}
 )
 
-install (FILES
+install(FILES
   ${CMAKE_CURRENT_SOURCE_DIR}/CMake/FLTK-Functions.cmake
   DESTINATION ${FLTK_CONFIG_PATH}
 )
 
 # Generate fltk-config
 
-set (prefix ${CMAKE_INSTALL_PREFIX})
-set (exec_prefix "\${prefix}")
-set (includedir "\${prefix}/${CMAKE_INSTALL_INCLUDEDIR}")
-set (BINARY_DIR)
-set (libdir "\${exec_prefix}/${CMAKE_INSTALL_LIBDIR}")
-set (srcdir ".")
+set(prefix ${CMAKE_INSTALL_PREFIX})
+set(exec_prefix "\${prefix}")
+set(includedir "\${prefix}/${CMAKE_INSTALL_INCLUDEDIR}")
+set(BINARY_DIR)
+set(libdir "\${exec_prefix}/${CMAKE_INSTALL_LIBDIR}")
+set(srcdir ".")
 
-set (LIBNAME "${libdir}/libfltk.a")
+set(LIBNAME "${libdir}/libfltk.a")
 
 configure_file(
   "${CMAKE_CURRENT_SOURCE_DIR}/fltk-config.in"
@@ -95,14 +96,14 @@ configure_file(
 )
 
 # Install fltk-config
-# Note: no need to set execute perms, install (PROGRAMS) does this
+# Note: no need to set execute perms, install(PROGRAMS) does this
 
-install (PROGRAMS
+install(PROGRAMS
   ${CMAKE_CURRENT_BINARY_DIR}/bin/fltk-config
   DESTINATION ${FLTK_BINDIR}
 )
 
-if (UNIX OR MSYS OR MINGW)
+if(UNIX OR MSYS OR MINGW)
   macro(INSTALL_MAN FILE LEVEL)
     install(FILES
       ${CMAKE_CURRENT_SOURCE_DIR}/documentation/src/${FILE}.man
@@ -111,20 +112,20 @@ if (UNIX OR MSYS OR MINGW)
     )
   endmacro (INSTALL_MAN FILE LEVEL)
 
-  if (FLTK_BUILD_FLUID)
+  if(FLTK_BUILD_FLUID)
     INSTALL_MAN (fluid 1)
-  endif (FLTK_BUILD_FLUID)
-  if (FLTK_BUILD_FLTK_OPTIONS)
+  endif(FLTK_BUILD_FLUID)
+  if(FLTK_BUILD_FLTK_OPTIONS)
     INSTALL_MAN (fltk-options 1)
-  endif (FLTK_BUILD_FLTK_OPTIONS)
+  endif(FLTK_BUILD_FLTK_OPTIONS)
   INSTALL_MAN (fltk-config 1)
   INSTALL_MAN (fltk 3)
 
-  if (FLTK_BUILD_TEST AND FLTK_BUILD_FLUID)
+  if(FLTK_BUILD_TEST AND FLTK_BUILD_FLUID)
     # Don't (!) install man pages of games (GitHub issue #23)
     # INSTALL_MAN (blocks 6)
     # INSTALL_MAN (checkers 6)
     # INSTALL_MAN (sudoku 6)
-  endif ()
+  endif()
 
-endif (UNIX OR MSYS OR MINGW)
+endif(UNIX OR MSYS OR MINGW)