CMake: build shared libs with OPTION_CAIROEXT (issue #250)

- remove separate libfltk_cairo to avoid cyclic dependencies, but
- keep a dummy libfltk_cairo in 1.4.0 for backwards compatibility
- move cairo/Fl_Cairo.cxx to src/Fl_Cairo.cxx
- add preliminary Cairo support for Visual Studio (MSVC)

Static linking is not affected by this change, but users building
with hand-made Makefiles will have to remove libfltk_cairo starting
with FLTK 1.4.0. The dummy library can be linked for backwards
compatibility but it will be removed later (in 1.4.x or 1.5.0).

The shared FLTK library libfltk.{so|dylib|dll|..} depends on libcairo
if and only if FLTK is built with one of the Cairo options. This has
always been the case for OPTION_CAIROEXT but is now also true if only
OPTION_CAIRO is selected, i.e. FLTK programs linked with a Cairo
enabled shared FLTK library will also be linked with libcairo. The same
is true for configure options --enable-cairo and --enable-cairoext,
respectively.

Preliminary Cairo support for MSVC now detects a Cairo installation
using the CMake variable FLTK_CAIRO_DIR which must be set by the user.
Note that this feature is temporary and may be changed in the future
for a better and more comfortable version.

2 files changed, 67 insertions, 27 deletions

diff --git a/CMake/fl_create_example.cmake b/CMake/fl_create_example.cmake
index 303b5ea41..77fb24d0b 100644
--- a/CMake/fl_create_example.cmake
+++ b/CMake/fl_create_example.cmake
@@ -1,8 +1,8 @@
 #
-# A macro used by the CMake build system for the Fast Light Tool Kit (FLTK).
-# Written by Michael Surette
+# A function used by the CMake build system for the Fast Light Tool Kit (FLTK).
+# Originally written by Michael Surette
 #
-# Copyright 1998-2020 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
@@ -17,7 +17,7 @@
 
 ################################################################################
 #
-# macro CREATE_EXAMPLE - Create a test/demo (example) program
+# function CREATE_EXAMPLE - Create a test/demo (example) program
 #
 # Input:
 #
@@ -119,13 +119,13 @@ function (CREATE_EXAMPLE NAME SOURCES LIBRARIES)
   set_target_properties   (${TARGET_NAME} PROPERTIES OUTPUT_NAME ${NAME})
   target_link_libraries   (${TARGET_NAME} ${LIBRARIES})
 
-  # we must link all programs with fltk_cairo if option CAIROEXT is enabled
+  # we must link all programs with cairo if option CAIROEXT is enabled
   if (FLTK_HAVE_CAIROEXT)
-    target_link_libraries (${TARGET_NAME} fltk_cairo cairo)
+    target_link_libraries (${TARGET_NAME} ${PKG_CAIRO_LIBRARIES})
   endif ()
 
-  if (FLTK_HAVE_CAIRO)
-    fl_target_link_directories (${TARGET_NAME} PRIVATE "${PKG_CAIRO_LIBRARY_DIRS}")
+  if (FLTK_HAVE_CAIRO AND PKG_CAIRO_LIBRARY_DIRS)
+    fl_target_link_directories (${TARGET_NAME} PUBLIC ${PKG_CAIRO_LIBRARY_DIRS})
   endif ()
 
   if (USE_GDIPLUS)        # can only be true on Windows
diff --git a/CMake/options.cmake b/CMake/options.cmake
index e0235236d..392cb5cd6 100644
--- a/CMake/options.cmake
+++ b/CMake/options.cmake
@@ -412,19 +412,8 @@ if (OPTION_CAIRO OR OPTION_CAIROEXT)
     if (OPTION_CAIROEXT)
       set (FLTK_HAVE_CAIROEXT 1)
     endif (OPTION_CAIROEXT)
-    add_subdirectory (cairo)
-
-    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()
 
+    ### FIXME ###
     include_directories (${PKG_CAIRO_INCLUDE_DIRS})
 
     # Cairo libs and flags for fltk-config
@@ -442,16 +431,67 @@ if (OPTION_CAIRO OR OPTION_CAIROEXT)
     string (REPLACE ";" " " CAIROLIBS  "${CAIROLIBS}")
     string (REPLACE ";" " " CAIROFLAGS "${PKG_CAIRO_CFLAGS}")
 
-    # fl_debug_var (FLTK_LDLIBS)
-    # fl_debug_var (CAIROFLAGS)
-    # fl_debug_var (CAIROLIBS)
+  else (PKG_CAIRO_FOUND)
+
+    if (NOT MSVC)
+      message (STATUS "*** Cairo was requested but not found - please check your cairo installation")
+      message (STATUS "***   or disable options OPTION_CAIRO and OPTION_CAIRO_EXT.")
+      message (FATAL_ERROR "*** Terminating: missing Cairo libs or headers.")
+    endif ()
+
+    # Tweak Cairo includes / libs / paths for Visual Studio (TEMPORARY solution).
+    # Todo: find a better way to set the required variables and flags!
+    # AlbrechtS 03/2023
+
+    message (STATUS "--- Cairo not found: trying to find Cairo for MSVC ...")
+
+    if (NOT FLTK_CAIRO_DIR)
+      message (STATUS "--- Please set FLTK_CAIRO_DIR to point at the Cairo installation folder ...")
+      message (STATUS "    ... with files 'include/cairo.h' and 'lib/x64/cairo.lib'")
+      message (STATUS "--- Example: cmake -DFLTK_CAIRO_DIR=\"C:/cairo-windows\" ...")
+      message (STATUS "--- Note: this will be changed in the future; currently only 64-bit supported")
+      message (FATAL_ERROR "*** Terminating: missing Cairo libs or headers.")
+    endif ()
+
+    set (CAIROLIBS "-lcairo")                             # should be correct: needs cairo.lib
+
+    # simulate results of 'pkg_search_module (PKG_CAIRO cairo)' and more (above)
+    # these variables will be used later
+
+    set (PKG_CAIRO_LIBRARIES "cairo")
+    set (PKG_CAIRO_INCLUDE_DIRS "${FLTK_CAIRO_DIR}/include")
+    set (PKG_CAIRO_LIBRARY_DIRS "${FLTK_CAIRO_DIR}/lib/x64/")
+
+    ### FIXME ###
+    include_directories (${PKG_CAIRO_INCLUDE_DIRS})
+
+    set (FLTK_HAVE_CAIRO 1)
+    if (OPTION_CAIROEXT)
+      set (FLTK_HAVE_CAIROEXT 1)
+    endif (OPTION_CAIROEXT)
 
-  else ()
-    message (STATUS "*** Cairo was requested but not found - please check your cairo installation")
-    message (STATUS "***   or disable options OPTION_CAIRO and OPTION_CAIRO_EXT.")
-    message (FATAL_ERROR "*** Terminating: missing Cairo libs or headers.")
   endif (PKG_CAIRO_FOUND)
 
+  if (0) # 1 = DEBUG, 0 = no output
+    message (STATUS "--- options.cmake: Cairo related variables ---")
+    if (MSVC)
+      fl_debug_var (FLTK_CAIRO_DIR)
+    endif (MSVC)
+    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)
+    message (STATUS "--- fltk-config/Cairo variables ---")
+    fl_debug_var (FLTK_LDLIBS)
+    fl_debug_var (CAIROFLAGS)
+    fl_debug_var (CAIROLIBS)
+    message (STATUS "--- End of Cairo related variables ---")
+  endif() # 1 = DEBUG, ...
+
 endif (OPTION_CAIRO OR OPTION_CAIROEXT)
 
 #######################################################################