Added ImageProcessor interface class and plugin mechnanism for ImageProcessor implementations to osgDB::Registry.

Add NVidiaTextureTools based plugin that provides an ImageProcessor implementation within an nvtt plugin.

CMakeModules/FindNVTT.cmake

@@ -0,0 +1,61 @@
+# Locate nvidia-texture-tools
+# This module defines
+# NVTT_LIBRARY
+# NVTT_FOUND, if false, do not try to link to nvtt
+# NVTT_INCLUDE_DIR, where to find the headers
+#
+
+
+FIND_PATH(NVTT_INCLUDE_DIR nvtt/nvtt.h
+  PATHS
+  /usr/local
+  /usr
+  $ENV{NVTT_DIR}
+  ${3rdPartyRoot}
+  PATH_SUFFIXES include
+)
+
+FIND_LIBRARY(NVTT_LIBRARY
+  NAMES nvtt
+  PATHS
+  /usr/local
+  /usr
+  $ENV{NVTT_DIR}
+  ${3rdPartyRoot}
+  PATH_SUFFIXES lib64 lib lib/shared lib/static lib64/static
+)
+
+FIND_LIBRARY(NVIMAGE_LIBRARY
+  NAMES nvimage
+  PATHS
+  /usr/local
+  /usr
+  $ENV{NVTT_DIR}
+  ${3rdPartyRoot}
+  PATH_SUFFIXES lib64 lib lib/shared lib/static lib64/static
+)
+
+FIND_LIBRARY(NVMATH_LIBRARY
+  NAMES nvmath
+  PATHS
+  /usr/local
+  /usr
+  $ENV{NVTT_DIR}
+  ${3rdPartyRoot}
+  PATH_SUFFIXES lib64 lib lib/shared lib/static lib64/static
+)
+
+FIND_LIBRARY(NVCORE_LIBRARY
+  NAMES nvcore
+  PATHS
+  /usr/local
+  /usr
+  $ENV{NVTT_DIR}
+  ${3rdPartyRoot}
+  PATH_SUFFIXES lib64 lib lib/shared lib/static lib64/static
+)
+
+SET(NVTT_FOUND "NO")
+IF(NVTT_LIBRARY AND NVTT_INCLUDE_DIR)
+  SET(NVTT_FOUND "YES")
+ENDIF(NVTT_LIBRARY AND NVTT_INCLUDE_DIR)