Merge pull request #268 from gonsolo/optix_from_environment

Read Optix path from environment.

CMakeLists.txt

@@ -18,7 +18,7 @@ option (PBRT_DBG_LOGGING "Enable (very verbose!) debug logging" OFF)
 option (PBRT_NVTX "Insert NVTX annotations for NVIDIA Profiling and Debugging Tools" OFF)
 option (PBRT_NVML "Use NVML for GPU performance measurement" OFF)
 option (PBRT_USE_PREGENERATED_RGB_TO_SPECTRUM_TABLES "Use pregenerated rgbspectrum_*.cpp files rather than running rgb2spec_opt to generate them at build time" OFF)
-set (PBRT_OPTIX7_PATH "" CACHE PATH "Path to OptiX 7 SDK")
+set (PBRT_OPTIX7_PATH $ENV{PBRT_OPTIX7_PATH} CACHE PATH "Path to OptiX 7 SDK")
 set (PBRT_GPU_SHADER_MODEL "" CACHE STRING "")
 
 if (NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)