Make PTex support optional

Basically makes configuration log much cleaner on systems
where PTex is not installed.

CMakeLists.txt

@@ -278,6 +278,7 @@ option(NO_EXAMPLES "Disable examples build" OFF)
 option(NO_REGRESSION "Disable regression tests build" OFF)
 option(NO_PYTHON "Disable Python SWIG build" OFF)
 option(NO_MAYA "Disable Maya plugin build" OFF)
+option(NO_PTEX "Disable PTex support" OFF)
 option(NO_DOC "Disable documentation build" OFF)
 option(NO_OMP "Disable OpenMP backend" OFF)
 option(NO_TBB "Disable TBB backend" OFF)
@@ -303,7 +304,9 @@ endif()
 if(NOT ANDROID AND NOT IOS)
     find_package(GLFW 2.7.0)
 endif()
-find_package(PTex 2.0)
+if(NOT NO_PTEX)
+   find_package(PTex 2.0)
+endif()
 find_package(PythonInterp 2.6)
 find_package(SWIG 1.3.40)
 find_package(Doxygen 1.8.4)
@@ -438,13 +441,14 @@ if(PTEX_FOUND)
         -DOPENSUBDIV_HAS_PTEX
     )
 else()
-    message(WARNING
-        "Ptex was not found : the OpenSubdiv Ptex example will not be "
-        "available.  If you do have Ptex installed and see this message, "
-        "please add your Ptex path to FindPTex.cmake in "
-        "${PROJECT_SOURCE_DIR}/cmake or set it through the PTEX_LOCATION "
-        "cmake command line argument or environment variable."
-    )
+    if(NOT NO_PTEX)
+        message(WARNING
+            "Ptex was not found : the OpenSubdiv Ptex example will not be "
+            "available.  If you do have Ptex installed and see this message, "
+            "please add your Ptex path to FindPTex.cmake in "
+            "${PROJECT_SOURCE_DIR}/cmake or set it through the PTEX_LOCATION "
+            "cmake command line argument or environment variable.")
+    endif()
 endif()
 
 if (NOT NO_MAYA)

README.md

@@ -59,6 +59,7 @@ Optional:
 -DNO_REGRESSION=1 // disable regression tests build
 -DNO_PYTHON=1     // disable Python SWIG build
 -DNO_MAYA=1       // disable Maya plugin build
+-DNO_PTEX=1       // disable PTex support
 -DNO_DOC=1        // disable documentation build
 -DNO_OMP=1        // disable OpenMP
 -DNO_CUDA=1       // disable CUDA

documentation/cmake_build.rst

@@ -119,6 +119,7 @@ The following configuration arguments can be passed to the cmake command line.
    -DNO_REGRESSION=1 // disable regression tests build
    -DNO_PYTHON=1     // disable Python SWIG build
    -DNO_MAYA=1       // disable Maya plugin build
+   -DNO_PTEX=1       // disable PTex support
    -DNO_DOC=1        // disable documentation build
    -DNO_OMP=1        // disable OpenMP
    -DNO_TBB=1        // disable TBB