If a feature is explicitly requested via the cmake command line, erro…

…r out if necessary libraries are missing and do not silently disable the requested feature.

CMakeLists.txt

@@ -141,8 +141,10 @@ find_package(ZLIB REQUIRED)
 find_package(Pixman REQUIRED)
 
 # Check for gettext
+if(DEFINED ENABLE_NLS)
 option(ENABLE_NLS "Enable translation of program messages" ON)
-if(ENABLE_NLS)
+endif()
+if(ENABLE_NLS OR NOT DEFINED ENABLE_NLS)
   # Tools
   find_package(Gettext)
 
@@ -176,18 +178,26 @@ if(ENABLE_NLS)
   endif()
 
   if(NOT GETTEXT_FOUND OR NOT ICONV_FOUND)
-    message(WARNING "Gettext NOT found.  Native Language Support disabled.")
-    set(ENABLE_NLS 0)
+    if(NOT DEFINED ENABLE_NLS)
+      message(WARNING "Gettext NOT found. Native Language Support disabled.")
+    else()
+      message(FATAL_ERROR "Native Language Support requested, but gettext NOT found!")
+    endif()
+    set(ENABLE_NLS OFF)
+  else()
+    set(ENABLE_NLS ON)
   endif()
 endif()
 
+if(DEFINED ENABLE_H264)
 option(ENABLE_H264 "Enable H.264 RFB encoding" ON)
-if(ENABLE_H264)
+endif()
+if(ENABLE_H264 OR NOT DEFINED ENABLE_H264)
   if(WIN32)
     add_definitions("-DHAVE_H264")
     set(H264_LIBS "WIN")  # may be LIBAV in the future
     set(H264_LIBRARIES ole32 mfplat mfuuid wmcodecdspuuid)
-
+    set(ENABLE_H264 ON)
     set(CMAKE_REQUIRED_LIBRARIES ${H264_LIBRARIES})
     check_variable_exists(CLSID_VideoProcessorMFT HAVE_VIDEO_PROCESSOR_MFT)
     set(CMAKE_REQUIRED_LIBRARIES)
@@ -203,9 +213,15 @@ if(ENABLE_H264)
       add_definitions("-D__STDC_CONSTANT_MACROS")
       add_definitions("-DHAVE_H264")
       set(H264_LIBS "LIBAV")
+      set(ENABLE_H264 ON)
     else()
-      set(H264_LIBS "NONE")
-      message(WARNING "FFMPEG support can't be found")
+      if(NOT DEFINED ENABLE_H264)
+        set(H264_LIBS "NONE")
+        message(WARNING "FFMPEG support can't be found. No H.264 RFB encoding support.")
+      else()
+        message(FATAL_ERROR "H.264 RFB encoding support requested, but FFMPEG support can't be found!")
+      endif()
+      set(ENABLE_H264 OFF)
     endif()
   endif()
   add_definitions("-DH264_${H264_LIBS}")
@@ -283,19 +299,38 @@ if(BUILD_VIEWER)
 endif()
 
 # Check for GNUTLS library
+if(DEFINED ENABLE_GNUTLS)
 option(ENABLE_GNUTLS "Enable protocol encryption and advanced authentication" ON)
-if(ENABLE_GNUTLS)
+endif()
+if(ENABLE_GNUTLS OR NOT DEFINED ENABLE_GNUTLS)
   find_package(GnuTLS)
   if (GNUTLS_FOUND)
     add_definitions("-DHAVE_GNUTLS")
+    set(ENABLE_GNUTLS ON)
+  else()
+    if(NOT DEFINED ENABLE_GNUTLS)
+      message(WARNING "GnuTLS NOT found. SSL support disabled.")
+    else()
+      message(FATAL_ERROR "GnuTLS support requested, but library could not be found!")
+    endif()
   endif()
 endif()
 
+if(DEFINED ENABLE_NETTLE)
 option(ENABLE_NETTLE "Enable RSA-AES security types" ON)
-if (ENABLE_NETTLE)
+endif()
+if(ENABLE_NETTLE OR NOT DEFINED ENABLE_NETTLE)
   find_package(Nettle)
   if (NETTLE_FOUND)
     add_definitions("-DHAVE_NETTLE")
+    set(ENABLE_NETTLE ON)
+  else()
+    if(NOT DEFINED ENABLE_NETTLE)
+      message(WARNING "Nettle library NOT found. RSA-AES security types disabled.")
+    else()
+      message(FATAL_ERROR "RSA-AES security types requested, but Nettle library could not be found!")
+    endif()
+    set(ENABLE_NETTLE OFF)
   endif()
 endif()