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 +141,8 @@ find_package(ZLIB REQUIRED)
 find_package(Pixman REQUIRED)
 
 # Check for gettext
-option(ENABLE_NLS "Enable translation of program messages" ON)
-if(ENABLE_NLS)
+set(ENABLE_NLS CACHE BOOL "Enable translation of program messages")
+if(ENABLE_NLS OR ENABLE_NLS STREQUAL "")
   # Tools
   find_package(Gettext)
 
@@ -176,13 +176,19 @@ 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(ENABLE_NLS OR ENABLE_NLS STREQUAL "")
+      message(WARNING "Gettext NOT found.  Native Language Support disabled.")
+      set(ENABLE_NLS OFF)
+    else()
+      message(FATAL_ERROR "Native Language Support requested, but gettext NOT found!")
+    endif()
+  else()
+    set(ENABLE_NLS ON)
   endif()
 endif()
 
-option(ENABLE_H264 "Enable H.264 RFB encoding" ON)
-if(ENABLE_H264)
+set(ENABLE_H264 CACHE BOOL "Enable H.264 RFB encoding")
+if(ENABLE_H264 OR ENABLE_H264 STREQUAL "")
   if(WIN32)
     add_definitions("-DHAVE_H264")
     set(H264_LIBS "WIN")  # may be LIBAV in the future
@@ -203,9 +209,14 @@ 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(ENABLE_H264 STREQUAL "")
+        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()
     endif()
   endif()
   add_definitions("-DH264_${H264_LIBS}")
@@ -283,19 +294,33 @@ if(BUILD_VIEWER)
 endif()
 
 # Check for GNUTLS library
-option(ENABLE_GNUTLS "Enable protocol encryption and advanced authentication" ON)
-if(ENABLE_GNUTLS)
+set(ENABLE_GNUTLS CACHE BOOL "Enable protocol encryption and advanced authentication")
+if(ENABLE_GNUTLS OR ENABLE_GNUTLS STREQUAL "")
   find_package(GnuTLS)
   if (GNUTLS_FOUND)
     add_definitions("-DHAVE_GNUTLS")
+    set(ENABLE_GNUTLS ON)
+  else()
+    if(ENABLE_GNUTLS STREQUAL "")
+      message(WARNING "GnuTLS NOT found. SSL support disabled.")
+    else()
+      message(FATAL_ERROR "GnuTLS support requested, but library could not be found!")
+    endif()
   endif()
 endif()
 
-option(ENABLE_NETTLE "Enable RSA-AES security types" ON)
-if (ENABLE_NETTLE)
+set(ENABLE_NETTLE CACHE BOOL "Enable RSA-AES security types")
+if(ENABLE_NETTLE OR ENABLE_NETTLE STREQUAL "")
   find_package(Nettle)
   if (NETTLE_FOUND)
     add_definitions("-DHAVE_NETTLE")
+    set(ENABLE_NETTLE ON)
+  else()
+    if(ENABLE_NETTLE STREQUAL "")
+      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()
   endif()
 endif()