Update Doxyfile.in from doxygen version 1.5.5 to 1.8.14

Most (if not all) doxygen tags introduced after 1.5.5 are commented out
  to avoid doxygen warnings about obsolete or unknown tags, except
  those tags that need a specific value.

Add 'HTML_COLORSTYLE = TOGGLE' (since 1.9.5) for better user experience.
  With this tag users can switch between dark and light mode *if*
  the docs were generated with doxygen 1.9.5 or later.

Enable search engine.

Log doxygen conversion errors and warnings to Doxy*_error.log,
  i.e. silence the doxygen conversion process.

documentation/src/index.dox: Remove background color from html
  index page for better contrast when using dark mode.

documentation/CMakeLists.txt

@@ -76,6 +76,7 @@ if (GENERATE_DOCS)
     string (REGEX REPLACE " .*$" "" DOXYGEN_VERSION_SHORT ${DOXYGEN_VERSION})
     # strip trailing newline
     string (REPLACE "\n" "" DOXYGEN_VERSION_SHORT "${DOXYGEN_VERSION_SHORT}")
+
   endif (DOXYGEN_FOUND)
 
   # configure copyright.dox (includes current year)
@@ -128,11 +129,13 @@ if (OPTION_BUILD_HTML_DOCUMENTATION)
 
   # convert Doxyfile to current doxygen version
 
+  set (LOGFILE ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile_error.log)
   add_custom_command (
     OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile
-    COMMAND ${DOXYGEN_EXECUTABLE} -u -s - < Doxyfile.in > Doxyfile
+    COMMAND ${DOXYGEN_EXECUTABLE} -u -s - < Doxyfile.in > Doxyfile 2> ${LOGFILE}
     WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
-    COMMENT "Converting Doxyfile to current doxygen version" VERBATIM
+    BYPRODUCTS ${LOGFILE}
+    COMMENT "Converting Doxyfile to doxygen version ${DOXYGEN_VERSION_SHORT}" VERBATIM
   )
 
   # generate HTML documentation
@@ -160,9 +163,6 @@ if (OPTION_BUILD_PDF_DOCUMENTATION)
   set (GENERATE_LATEX YES)
   set (LATEX_HEADER   "${CMAKE_CURRENT_BINARY_DIR}/fltk-book.tex")
 
-  # strip potential " (Git-hash)" from the original version
-  string (REGEX REPLACE " .*$" "" DOXY_VERSION ${DOXYGEN_VERSION})
-
   # configure Doxygen input file for PDF docs (Doxybook.in)
 
   configure_file (
@@ -173,11 +173,13 @@ if (OPTION_BUILD_PDF_DOCUMENTATION)
 
   # convert Doxybook to current doxygen version
 
+  set (LOGFILE ${CMAKE_CURRENT_BINARY_DIR}/Doxybook_error.log)
   add_custom_command (
     OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/Doxybook
-    COMMAND ${DOXYGEN_EXECUTABLE} -u -s - < Doxybook.in > Doxybook
+    COMMAND ${DOXYGEN_EXECUTABLE} -u -s - < Doxybook.in > Doxybook 2> ${LOGFILE}
     WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
-    COMMENT "Converting Doxybook to current doxygen version" VERBATIM
+    BYPRODUCTS ${LOGFILE}
+    COMMENT "Converting Doxybook to doxygen version ${DOXYGEN_VERSION_SHORT}" VERBATIM
   )
 
   # generate LaTeX title fltk-title.tex

documentation/Makefile

@@ -149,7 +149,7 @@ uninstall-linux uninstall-osx:
 
 Doxyfile: Doxyfile.in generated.dox copyright.dox
 	echo "Generating Doxyfile ..."
-	$(DOXYDOC) -u -s - < $< | \
+	$(DOXYDOC) -u -s - < $< 2>Doxyfile_error.log | \
 	sed -e's,@FLTK_VERSION@,$(FLTK_VERSION),' \
 	    -e's,@GENERATE_HTML@,YES,' \
 	    -e's,@GENERATE_LATEX@,NO,' \
@@ -162,7 +162,7 @@ Doxyfile: Doxyfile.in generated.dox copyright.dox
 
 Doxybook: Doxyfile.in generated.dox copyright.dox
 	echo "Generating Doxybook ..."
-	$(DOXYDOC) -u -s - < $< | \
+	$(DOXYDOC) -u -s - < $< 2>Doxybook_error.log | \
 	sed -e's,@FLTK_VERSION@,$(FLTK_VERSION),' \
 	    -e's,@GENERATE_HTML@,NO,' \
 	    -e's,@GENERATE_LATEX@,YES,' \

documentation/src/index.dox

@@ -1,7 +1,7 @@
 /**
 
 \mainpage FLTK Programming Manual
-<TABLE BGCOLOR="#9f9f9f" CELLPADDING="8" CELLSPACING="0" SUMMARY="TITLE BAR" WIDTH="100%" BORDER="0">
+<TABLE CELLPADDING="8" CELLSPACING="0" SUMMARY="TITLE BAR" WIDTH="100%" BORDER="0">
 <TR>
   <TD><CENTER>
     \image html FL200.png
@@ -17,7 +17,7 @@
   </CENTER></TD>
 </TR>
 </TABLE>
-<TABLE BGCOLOR="#9f9f9f" CELLPADDING="8" CELLSPACING="0" SUMMARY="TITLE BAR" WIDTH="100%" BORDER="0">
+<TABLE CELLPADDING="8" CELLSPACING="0" SUMMARY="TITLE BAR" WIDTH="100%" BORDER="0">
 <TR>
   <TD style="text-align: center;">
     This software and manual are provided under the terms of the GNU
@@ -27,7 +27,7 @@
   </TD>
 </TR>
 </TABLE>
-<TABLE BGCOLOR="#9f9fef" CELLPADDING="8" CELLSPACING="0" SUMMARY="Table of Contents" WIDTH="100%" BORDER="0">
+<TABLE CELLPADDING="8" CELLSPACING="0" SUMMARY="Table of Contents" WIDTH="100%" BORDER="0">
 <TR>
   <TD ALIGN="LEFT" VALIGN="TOP">