Add CMake variable and C++ macro VTK_RENDERING_BACKEND_OPENGL_VERSION

These can be used at configuration and compilation times to adjust for
the currently used backend.

Author: taketwo

CMakeLists.txt

@@ -361,7 +361,12 @@ option(WITH_VTK "Build VTK-Visualizations" TRUE)
 if(WITH_VTK AND NOT ANDROID)
   find_package(VTK)
   if(VTK_FOUND)
-    message(STATUS "VTK_MAJOR_VERSION ${VTK_MAJOR_VERSION}")
+    if(NOT DEFINED VTK_RENDERING_BACKEND)
+      # On old VTK versions this variable does not exist. In this case it is
+      # safe to assume OpenGL backend
+      set(VTK_RENDERING_BACKEND "OpenGL")
+    endif()
+    message(STATUS "VTK_MAJOR_VERSION ${VTK_MAJOR_VERSION}, rendering backend: ${VTK_RENDERING_BACKEND}")
     if (PCL_SHARED_LIBS OR
         (NOT (PCL_SHARED_LIBS) AND NOT (VTK_BUILD_SHARED_LIBS)))
       set(VTK_FOUND TRUE)
@@ -377,6 +382,11 @@ if(WITH_VTK AND NOT ANDROID)
           option (VTK_USE_COCOA "Use Cocoa for VTK render windows" ON)
           MARK_AS_ADVANCED (VTK_USE_COCOA)
       endif (APPLE)
+      if(${VTK_RENDERING_BACKEND} STREQUAL "OpenGL")
+        set(VTK_RENDERING_BACKEND_OPENGL_VERSION "1")
+      elseif(${VTK_RENDERING_BACKEND} STREQUAL "OpenGL2")
+        set(VTK_RENDERING_BACKEND_OPENGL_VERSION "2")
+      endif()
       set(HAVE_VTK ON)
     else ()
       set(VTK_FOUND OFF)

pcl_config.h.in

@@ -71,3 +71,7 @@
 /* Address the cases where on MacOS and OpenGL and GLUT are not frameworks */
 #cmakedefine OPENGL_IS_A_FRAMEWORK
 #cmakedefine GLUT_IS_A_FRAMEWORK
+
+/* Version of OpenGL used by VTK as rendering backend */
+#define VTK_RENDERING_BACKEND_OPENGL_VERSION ${VTK_RENDERING_BACKEND_OPENGL_VERSION}
+