From 7b8f3de97be7d8799e40a4a60e2ad5d35fb3456d Mon Sep 17 00:00:00 2001
From: Carl Hetherington <cth@carlh.net>
Date: Tue, 18 Nov 2025 23:09:26 +0100
Subject: Add and test relative_path() method.

---
 src/lib/util.cc | 12 ++++++++++++
 src/lib/util.h  |  9 +++++++++
 2 files changed, 21 insertions(+)

(limited to 'src')

diff --git a/src/lib/util.cc b/src/lib/util.cc
index 8628ee3e0..ef12e63ad 100644
--- a/src/lib/util.cc
+++ b/src/lib/util.cc
@@ -1180,3 +1180,15 @@ force(AVPixelFormat format)
 	return [format](AVPixelFormat) { return format; };
 }
 
+
+boost::filesystem::path
+relative_path(boost::filesystem::path const& path, boost::filesystem::path const& base)
+{
+	auto relative = boost::filesystem::relative(path, base);
+	if (relative == boost::filesystem::path()) {
+		return path;
+	}
+
+	return relative;
+}
+
diff --git a/src/lib/util.h b/src/lib/util.h
index 846059e1a..f6c8e573f 100644
--- a/src/lib/util.h
+++ b/src/lib/util.h
@@ -103,6 +103,15 @@ extern std::string rfc_2822_date(time_t time);
 bool paths_exist(std::vector<boost::filesystem::path> const& paths);
 std::function<AVPixelFormat (AVPixelFormat)> force(AVPixelFormat format);
 
+/** @param path Some path.
+ *  @param base Some base path.
+ *  @return path relative to base, if possible, otherwise path.
+ *
+ *  This wraps boost::filesystem::path which returns an empty path if you try to get an impossible
+ *  relative path on Windows (e.g. X:\foo relative to C:\bar).
+ */
+boost::filesystem::path relative_path(boost::filesystem::path const& path, boost::filesystem::path const& base);
+
 
 template <class T>
 T
-- 
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