Fix cairo build (autoconf + CMake) + README's

- rewrite to use pkg-config with both autoconf + CMake
- remove hardcoded library names
- fix build dependencies and search directories
- remove or replace old and unused variables
- update README files

To be done:
- implement fallback for autoconf/configure if pkg-config is missing
- fix pango build (uses cairo internally)

4 files changed, 66 insertions, 25 deletions

diff --git a/CMake/fl_create_example.cmake b/CMake/fl_create_example.cmake
index dd4e1bc42..9053fa790 100644
--- a/CMake/fl_create_example.cmake
+++ b/CMake/fl_create_example.cmake
@@ -115,6 +115,10 @@ macro (CREATE_EXAMPLE NAME SOURCES LIBRARIES)
   set_target_properties   (${TARGET_NAME} PROPERTIES OUTPUT_NAME ${NAME})
   target_link_libraries   (${TARGET_NAME} ${LIBRARIES})
 
+  if (FLTK_HAVE_CAIRO)
+    target_link_directories (${TARGET_NAME} PUBLIC ${PKG_CAIRO_LIBRARY_DIRS})
+  endif (FLTK_HAVE_CAIRO)
+
   if (ICON_PATH)
     set_target_properties (${TARGET_NAME} PROPERTIES MACOSX_BUNDLE_ICON_FILE ${ICON_NAME})
     set_target_properties (${TARGET_NAME} PROPERTIES RESOURCE ${ICON_PATH})
diff --git a/CMake/fl_debug_var.cmake b/CMake/fl_debug_var.cmake
index 4cecf3c7a..865f2a895 100644
--- a/CMake/fl_debug_var.cmake
+++ b/CMake/fl_debug_var.cmake
@@ -21,7 +21,7 @@
 #
 # This macro displays the name and value of a CMake variable.
 # The variable name is expanded with spaces to be (at least)
-# <min_len> (currently 24) characters wide for better readability.
+# <min_len> (currently 30) characters wide for better readability.
 # VARNAME must be a string literal, e.g. WIN32 or "WIN32".
 #
 # Syntax:
@@ -34,7 +34,7 @@
 #######################################################################
 
 macro (fl_debug_var name)
-  set (min_len 24)
+  set (min_len 30)
   set (var "${name}")
   string(LENGTH "${var}" len)
   while (len LESS min_len)
diff --git a/CMake/options.cmake b/CMake/options.cmake
index 142f345ee..008088a45 100644
--- a/CMake/options.cmake
+++ b/CMake/options.cmake
@@ -145,37 +145,63 @@ if (OPTION_BUILD_HTML_DOCUMENTATION OR OPTION_BUILD_PDF_DOCUMENTATION)
 endif (OPTION_BUILD_HTML_DOCUMENTATION OR OPTION_BUILD_PDF_DOCUMENTATION)
 
 #######################################################################
-include (FindPkgConfig)
+# Include optional Cairo support
+#######################################################################
 
 option (OPTION_CAIRO "use lib Cairo" OFF)
 option (OPTION_CAIROEXT
   "use FLTK code instrumentation for Cairo extended use" OFF
 )
 
-if ((OPTION_CAIRO OR OPTION_CAIROEXT) AND LIB_CAIRO)
+set (FLTK_HAVE_CAIRO 0)
+set (FLTK_USE_CAIRO 0)
+
+if (OPTION_CAIRO OR OPTION_CAIROEXT)
   pkg_search_module (PKG_CAIRO cairo)
-endif ((OPTION_CAIRO OR OPTION_CAIROEXT) AND LIB_CAIRO)
-
-if (PKG_CAIRO_FOUND)
-  set (FLTK_HAVE_CAIRO 1)
-  add_subdirectory (cairo)
-  list (APPEND FLTK_LDLIBS -lcairo -lpixman-1)
-  include_directories (${PKG_CAIRO_INCLUDE_DIRS})
-  string (REPLACE ";" " " CAIROFLAGS "${PKG_CAIRO_CFLAGS}")
-
-  if (LIB_CAIRO AND OPTION_CAIROEXT)
-    set (FLTK_USE_CAIRO 1)
-    set (FLTK_CAIRO_FOUND TRUE)
+
+  # fl_debug_var (PKG_CAIRO_FOUND)
+
+  if (PKG_CAIRO_FOUND)
+    set (FLTK_HAVE_CAIRO 1)
+    if (OPTION_CAIROEXT)
+      set (FLTK_USE_CAIRO 1)
+    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)
+
+    include_directories (${PKG_CAIRO_INCLUDE_DIRS})
+
+    # Cairo libs and flags for fltk-config
+
+    # Hint: use either PKG_CAIRO_* or PKG_CAIRO_STATIC_* variables to
+    # create the list of libraries used to link programs with cairo
+    # by running fltk-config --use-cairo --compile ...
+    # Currently we're using the non-STATIC variables to link cairo shared.
+
+    set (CAIROLIBS)
+    foreach (lib ${PKG_CAIRO_LIBRARIES})
+      list (APPEND CAIROLIBS "-l${lib}")
+    endforeach()
+
+    string (REPLACE ";" " " CAIROLIBS  "${CAIROLIBS}")
+    string (REPLACE ";" " " CAIROFLAGS "${PKG_CAIRO_CFLAGS}")
+
+    # fl_debug_var (FLTK_LDLIBS)
+    # fl_debug_var (CAIROFLAGS)
+    # fl_debug_var (CAIROLIBS)
+
   else ()
-    set (FLTK_CAIRO_FOUND FALSE)
-  endif (LIB_CAIRO AND OPTION_CAIROEXT)
-else ()
-  if (OPTION_CAIRO OR OPTION_CAIROEXT)
     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 (OPTION_CAIRO OR OPTION_CAIROEXT)
-endif (PKG_CAIRO_FOUND)
+  endif (PKG_CAIRO_FOUND)
+
+endif (OPTION_CAIRO OR OPTION_CAIROEXT)
 
 #######################################################################
 option (OPTION_USE_SVG "read/write SVG files" ON)
diff --git a/CMake/resources.cmake b/CMake/resources.cmake
index 3ec95b3b6..57173f206 100644
--- a/CMake/resources.cmake
+++ b/CMake/resources.cmake
@@ -2,7 +2,7 @@
 # Resource definitions to build the FLTK project using CMake (www.cmake.org)
 # Written by Michael Surette
 #
-# Copyright 1998-2020 by Bill Spitzak and others.
+# 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
@@ -35,7 +35,19 @@ macro (fl_find_header VAR HEADER)
   endif (NOT CMAKE_REQUIRED_QUIET)
 endmacro (fl_find_header)
 
+#######################################################################
+# Include FindPkgConfig for later use of pkg-config
+#######################################################################
+
+include (FindPkgConfig)
+
+# fl_debug_var (PKG_CONFIG_FOUND)
+# fl_debug_var (PKG_CONFIG_EXECUTABLE)
+# fl_debug_var (PKG_CONFIG_VERSION_STRING)
+
+#######################################################################
 # Find header files...
+#######################################################################
 
 fl_find_header (HAVE_ALSA_ASOUNDLIB_H alsa/asoundlib.h)
 fl_find_header (HAVE_DLFCN_H dlfcn.h)
@@ -150,7 +162,6 @@ mark_as_advanced (FREETYPE_PATH)
 
 #######################################################################
 # libraries
-find_library (LIB_CAIRO cairo)
 find_library (LIB_dl dl)
 if ((NOT APPLE) OR OPTION_APPLE_X11)
   find_library (LIB_fontconfig fontconfig)
@@ -163,7 +174,7 @@ find_library (LIB_jpeg jpeg)
 find_library (LIB_png png)
 find_library (LIB_zlib z)
 
-mark_as_advanced (LIB_CAIRO LIB_dl LIB_fontconfig LIB_freetype)
+mark_as_advanced (LIB_dl LIB_fontconfig LIB_freetype)
 mark_as_advanced (LIB_GL LIB_MesaGL LIB_GLEW)
 mark_as_advanced (LIB_jpeg LIB_png LIB_zlib)