Improved cmake error messages about CUDA support.

dlib/CMakeLists.txt

@@ -561,7 +561,7 @@ if (NOT TARGET dlib)
 
             include(cmake_utils/test_for_cudnn/find_cudnn.txt)
 
-            if (cudnn AND NOT DEFINED cuda_test_compile_worked AND NOT DEFINED cudnn_test_compile_worked)
+            if (cudnn AND cudnn_include AND NOT DEFINED cuda_test_compile_worked AND NOT DEFINED cudnn_test_compile_worked)
                # make sure cuda is really working by doing a test compile
                message(STATUS "Building a CUDA test project to see if your compiler is compatible with CUDA...")
 
@@ -585,10 +585,10 @@ if (NOT TARGET dlib)
                               ${PROJECT_SOURCE_DIR}/cmake_utils/test_for_cudnn cudnn_test
                               CMAKE_FLAGS ${CUDA_TEST_CMAKE_FLAGS}
                                           )
-                  if (cudnn_test_compile_worked)
-                     message(STATUS "Found cuDNN: " ${cudnn})
-                  else()
-                     message(STATUS "*** Found cuDNN, but it looks like the wrong version so dlib will not use it. ***")
+                  if (NOT cudnn_test_compile_worked)
+                     message(STATUS "*** Found cuDNN, but it looks like the wrong version so dlib will not use it.              ***")
+                     message(STATUS "*** Dlib requires cuDNN V5.0 OR GREATER.  Since cuDNN is not found DLIB WILL NOT USE CUDA. ***")
+                     message(STATUS "*** If you have cuDNN then set CMAKE_PREFIX_PATH to include cuDNN's folder.                ***")
                   endif()
                endif()
             endif()
@@ -632,19 +632,14 @@ if (NOT TARGET dlib)
                                       ${openmp_libarires}
                                       )
             include_directories(${cudnn_include})
+            message(STATUS "Enabling CUDA support for dlib.  DLIB WILL USE CUDA")
          else()
             set(DLIB_USE_CUDA OFF CACHE STRING ${DLIB_USE_BLAS_STR} FORCE )
             toggle_preprocessor_switch(DLIB_USE_CUDA)
-            if (NOT USING_OLD_VISUAL_STUDIO_COMPILER)
-               if (cuda_test_compile_worked)
-                  if (NOT cudnn OR NOT cudnn_include OR NOT cudnn_test_compile_worked)
-                     message(STATUS "*** cuDNN V5.0 OR GREATER NOT FOUND.  DLIB WILL NOT USE CUDA. ***")
-                     message(STATUS "*** If you have cuDNN then set CMAKE_PREFIX_PATH to include cuDNN's folder.")
-                  endif()
-               endif()
-            else ()
+            if (USING_OLD_VISUAL_STUDIO_COMPILER)
                message(STATUS "*** Dlib CUDA support requires C++11 but your compiler doesn't support it. ***")
             endif()
+            message(STATUS "Disabling CUDA support for dlib.  DLIB WILL NOT USE CUDA")
          endif()
       endif()
       

dlib/cmake_utils/test_for_cudnn/find_cudnn.txt

@@ -14,3 +14,11 @@ find_library(cudnn cudnn
     PATH_SUFFIXES lib64 lib x64
     )
 mark_as_advanced(cudnn cudnn_include)
+
+if (cudnn AND cudnn_include)
+    message(STATUS "Found cuDNN: " ${cudnn})
+else()
+    message(STATUS "*** cuDNN V5.0 OR GREATER NOT FOUND.                                                       ***")
+    message(STATUS "*** Dlib requires cuDNN V5.0 OR GREATER.  Since cuDNN is not found DLIB WILL NOT USE CUDA. ***")
+    message(STATUS "*** If you have cuDNN then set CMAKE_PREFIX_PATH to include cuDNN's folder.                ***")
+endif()