Add CMake flag FORCE_OPENGL_ENABLED

CMakeLists.txt

@@ -60,6 +60,7 @@ option(IPO_ENABLED "Whether to enable interprocedural optimization" ON)
 option(CUDA_ENABLED "Whether to enable CUDA, if available" ON)
 option(GUI_ENABLED "Whether to enable the graphical UI" ON)
 option(OPENGL_ENABLED "Whether to enable OpenGL, if available" ON)
+option(FORCE_OPENGL_ENABLED "Force enable OpenGL even if GUI_ENABLED=OFF" OFF)
 option(TESTS_ENABLED "Whether to build test binaries" OFF)
 option(ASAN_ENABLED "Whether to enable AddressSanitizer flags" OFF)
 option(PROFILING_ENABLED "Whether to enable google-perftools linker flags" OFF)
@@ -131,7 +132,7 @@ if(GUI_ENABLED)
     endif()
 endif()
 
-if(OPENGL_ENABLED AND NOT GUI_ENABLED)
+if(OPENGL_ENABLED AND NOT GUI_ENABLED AND NOT FORCE_OPENGL_ENABLED)
     message(STATUS "Disabling GUI will also disable OpenGL")
     set(OPENGL_ENABLED OFF)
 endif()
@@ -286,7 +287,7 @@ else()
     set(CGAL_ENABLED OFF)
 endif()
 
-if(Qt5_FOUND)
+if(GUI_ENABLED AND Qt5_FOUND)
     # Qt5 was built with -reduce-relocations.
     if(Qt5_POSITION_INDEPENDENT_CODE)
         set(CMAKE_POSITION_INDEPENDENT_CODE ON)
@@ -297,6 +298,11 @@ if(Qt5_FOUND)
 
     # Enable automatic compilation of Qt resource files.
     set(CMAKE_AUTORCC ON)
+else()
+    set(CMAKE_POSITION_INDEPENDENT_CODE ON)
+    if(CUDA_ENABLED AND NOT IS_MSVC)
+        set(CUDA_NVCC_FLAGS "${CUDA_NVCC_FLAGS} --compiler-options -fPIC")
+    endif()
 endif()
 
 ################################################################################

src/feature/sift.cc

@@ -36,9 +36,7 @@
 #include <memory>
 
 #include "FLANN/flann.hpp"
-#if !defined(GUI_ENABLED) && !defined(CUDA_ENABLED)
 #include "GL/glew.h"
-#endif
 #include "SiftGPU/SiftGPU.h"
 #include "VLFeat/covdet.h"
 #include "VLFeat/sift.h"