From https://developer.blender.org/rB74caf773619bbf6a0f95c598b66261a6bef392ee
From: Brecht Van Lommel <brecht@blender.org>
Date: Mon, 29 Aug 2022 19:12:15 +0200
Subject: [PATCH 001/539] Cycles: add option to specify OptiX runtime root
 directory

This allows individual users or Linux distributions to specify a directory
Cycles will automatically look for the OptiX include folder, to compile kernels
at runtime.

It is still possible to override this with the OPTIX_ROOT_DIR environment
variable at runtime.

Based on patch by Sebastian Parborg.

Ref D15792
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -435,10 +435,16 @@ if(NOT APPLE)
   option(WITH_CYCLES_CUBIN_COMPILER    "Build cubins with nvrtc based compiler instead of nvcc" OFF)
   option(WITH_CYCLES_CUDA_BUILD_SERIAL "Build cubins one after another (useful on machines with limited RAM)" OFF)
   option(WITH_CUDA_DYNLOAD             "Dynamically load CUDA libraries at runtime (for developers, makes cuda-gdb work)" ON)
+
+  set(OPTIX_ROOT_DIR                   "" CACHE PATH "Path to the OptiX SDK root directory, for building Cycles OptiX kernels.")
+  set(CYCLES_RUNTIME_OPTIX_ROOT_DIR    "" CACHE PATH "Path to the OptiX SDK root directory. When set, this path will be used at runtime to compile OptiX kernels.")
+
   mark_as_advanced(CYCLES_CUDA_BINARIES_ARCH)
   mark_as_advanced(WITH_CYCLES_CUBIN_COMPILER)
   mark_as_advanced(WITH_CYCLES_CUDA_BUILD_SERIAL)
   mark_as_advanced(WITH_CUDA_DYNLOAD)
+  mark_as_advanced(OPTIX_ROOT_DIR)
+  mark_as_advanced(CYCLES_RUNTIME_OPTIX_ROOT_DIR)
 endif()
 
 # AMD HIP
--- a/intern/cycles/device/CMakeLists.txt
+++ b/intern/cycles/device/CMakeLists.txt
@@ -19,6 +19,8 @@ if(WITH_CYCLES_DEVICE_OPTIX OR WITH_CYCLES_DEVICE_CUDA)
     )
     add_definitions(-DCYCLES_CUDA_NVCC_EXECUTABLE="${CUDA_NVCC_EXECUTABLE}")
   endif()
+
+  add_definitions(-DCYCLES_RUNTIME_OPTIX_ROOT_DIR="${CYCLES_RUNTIME_OPTIX_ROOT_DIR}")
 endif()
 
 if(WITH_CYCLES_DEVICE_HIP AND WITH_HIP_DYNLOAD)
--- a/intern/cycles/device/optix/device_impl.cpp
+++ b/intern/cycles/device/optix/device_impl.cpp
@@ -342,15 +342,29 @@ BVHLayoutMask OptiXDevice::get_bvh_layout_mask() const
   return BVH_LAYOUT_OPTIX;
 }
 
+static string get_optix_include_dir()
+{
+  const char *env_dir = getenv("OPTIX_ROOT_DIR");
+  const char *default_dir = CYCLES_RUNTIME_OPTIX_ROOT_DIR;
+
+  if (env_dir && env_dir[0]) {
+    const string env_include_dir = path_join(env_dir, "include");
+    return env_include_dir;
+  }
+  else if (default_dir[0]) {
+    const string default_include_dir = path_join(default_dir, "include");
+    return default_include_dir;
+  }
+
+  return string();
+}
+
 string OptiXDevice::compile_kernel_get_common_cflags(const uint kernel_features)
 {
   string common_cflags = CUDADevice::compile_kernel_get_common_cflags(kernel_features);
 
   /* Add OptiX SDK include directory to include paths. */
-  const char *optix_sdk_path = getenv("OPTIX_ROOT_DIR");
-  if (optix_sdk_path) {
-    common_cflags += string_printf(" -I\"%s/include\"", optix_sdk_path);
-  }
+  common_cflags += string_printf(" -I\"%s/include\"", get_optix_include_dir().c_str());
 
   /* Specialization for shader raytracing. */
   if (kernel_features & KERNEL_FEATURE_NODE_RAYTRACE) {
@@ -460,10 +474,19 @@ bool OptiXDevice::load_kernels(const uint kernel_features)
                              "lib/kernel_optix_shader_raytrace.ptx" :
                              "lib/kernel_optix.ptx");
     if (use_adaptive_compilation() || path_file_size(ptx_filename) == -1) {
-      if (!getenv("OPTIX_ROOT_DIR")) {
+      std::string optix_include_dir = get_optix_include_dir();
+      if (optix_include_dir.empty()) {
         set_error(
-            "Missing OPTIX_ROOT_DIR environment variable (which must be set with the path to "
-            "the Optix SDK to be able to compile Optix kernels on demand).");
+            "Unable to compile OptiX kernels at runtime. Set OPTIX_ROOT_DIR environment variable "
+            "to a directory containing the OptiX SDK.");
+        return false;
+      }
+      else if (!path_is_directory(optix_include_dir)) {
+        set_error(string_printf(
+            "OptiX headers not found at %s, unable to compile OptiX kernels at runtime. Install "
+            "OptiX SDK in the specified location, or set OPTIX_ROOT_DIR environment variable to a "
+            "directory containing the OptiX SDK.",
+            optix_include_dir.c_str()));
         return false;
       }
       ptx_filename = compile_kernel(
-- 
2.37.3