CMake: test jpeglib.h header for TurboVNC if compile check fails

Author: Christian Beier

CMakeLists.txt

@@ -106,7 +106,16 @@ if(WITH_JPEG)
     set(CMAKE_REQUIRED_DEFINITIONS)
 
     if(NOT FOUND_LIBJPEG_TURBO)
-      message(WARNING "*** The libjpeg library you are building against is not libjpeg-turbo.  Performance will be reduced.  You can obtain libjpeg-turbo from:  https://sourceforge.net/projects/libjpeg-turbo/files/ ***")
+      # last-resort grep check (when using LibVNCServer as a CMake subdir together with turbojpeg CMake subdir, the build check above fails since turbojpeg is not yet built when LibVNCServer is configured)
+      if(JPEG_INCLUDE_DIR MATCHES "\..*") # is relative?
+        set(JPEGLIB_H_PATH "${CMAKE_SOURCE_DIR}/${JPEG_INCLUDE_DIR}/jpeglib.h")
+      else()
+	set(JPEGLIB_H_PATH "${JPEG_INCLUDE_DIR}/jpeglib.h")
+      endif()
+      file(STRINGS ${JPEGLIB_H_PATH} FOUND_LIBJPEG_TURBO REGEX "JCS_EXT_RGB")
+      if(NOT FOUND_LIBJPEG_TURBO)
+	message(WARNING "*** The libjpeg library you are building against is not libjpeg-turbo.  Performance will be reduced.  You can obtain libjpeg-turbo from:  https://sourceforge.net/projects/libjpeg-turbo/files/ ***")
+      endif()
     endif()
   endif(JPEG_FOUND)
 endif(WITH_JPEG)