luxrays: rename GetConfigDir as GetCacheDir and use XDG_CACHE_HOME according to specifications

include/luxrays/utils/config.h

@@ -28,7 +28,9 @@
 namespace luxrays {
 
 extern std::string SanitizeFileName(const std::string &name);
-extern std::filesystem::path GetConfigDir();
+
+extern std::filesystem::path GetCacheDir();
+
 
 }
 

src/luxrays/utils/config.cpp

@@ -40,12 +40,39 @@ string SanitizeFileName(const string &name) {
 	return sanitizedName;
 }
 
-std::filesystem::path GetConfigDir() {
+std::filesystem::path GetEnvPath(const string &name) {
+	char *path = getenv(name.c_str());
+
+	if (path && path[0]) {
+		return std::filesystem::path(path);
+	}
+
+	return "";
+}
+
+std::filesystem::path GetCacheDir() {
+
 #if defined(__linux__)
 	// std::filesystem::temp_directory_path() is usually mapped to /tmp and
 	// the content of the directory is often deleted at each reboot
-	std::filesystem::path kernelConfigDir = getenv("HOME");
-	kernelConfigDir = kernelConfigDir / ".config" / "luxcorerender.org";
+
+	// XDG standard says XDG_CACHE_HOME is unset by default.
+	std::filesystem::path xdgCacheHome = GetEnvPath("XDG_CACHE_HOME");
+
+	if (!xdgCacheHome.size()) {
+		// HOME should never be unset, but we better not want to
+		// crash if that happens.
+		std::filesystem::path home = GetEnvPath("HOME");
+
+		if (home.size()) {
+			xdgCacheHome = home / ".config";
+		}
+		else {
+			xdgCacheHome = std::filesystem::temp_directory_path();
+		}
+	}
+
+	std::filesystem::path kernelConfigDir = xdgCacheHome / "luxcorerender.org";
 #elif defined(__APPLE__)
 	// std::filesystem::temp_directory_path() is usually mapped to /tmp and
 	// the content of the directory is deleted at each reboot on MacOS

src/luxrays/utils/cuda.cpp

@@ -136,7 +136,7 @@ bool cudaKernelCache::ForcedCompilePTX(const vector<string> &kernelsParameters,
 //------------------------------------------------------------------------------
 
 std::filesystem::path cudaKernelPersistentCache::GetCacheDir(const string &applicationName) {
-	return GetConfigDir() / "cuda_kernel_cache" / SanitizeFileName(applicationName);
+	return luxrays::GetCacheDir() / "cuda_kernel_cache" / SanitizeFileName(applicationName);
 }
 
 cudaKernelPersistentCache::cudaKernelPersistentCache(const string &applicationName) {

src/luxrays/utils/ocl.cpp

@@ -202,7 +202,7 @@ cl_program oclKernelCache::ForcedCompile(cl_context context, cl_device_id device
 //------------------------------------------------------------------------------
 
 std::filesystem::path oclKernelPersistentCache::GetCacheDir(const string &applicationName) {
-	return GetConfigDir() / "ocl_kernel_cache" / SanitizeFileName(applicationName);
+	return luxrays::GetCacheDir() / "ocl_kernel_cache" / SanitizeFileName(applicationName);
 }
 
 oclKernelPersistentCache::oclKernelPersistentCache(const string &applicationName) {