From b4d95c3842577e0fcb71e2d3e4adda7c82a661ba Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Sat, 14 Feb 2026 20:13:10 +0000
Subject: Add support for partitioning by 2 unary predicates

Second predicate creates a single block of truthy values in the middle,
and two falsy blocks at each end.
---
 gfx/gl/instanceVertices.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

(limited to 'gfx')

diff --git a/gfx/gl/instanceVertices.h b/gfx/gl/instanceVertices.h
index 629c664..de20871 100644
--- a/gfx/gl/instanceVertices.h
+++ b/gfx/gl/instanceVertices.h
@@ -2,6 +2,7 @@
 
 #include "glContainer.h"
 #include <cassert>
+#include <functional>
 #include <special_members.h>
 #include <utility>
 
@@ -133,6 +134,19 @@ public:
 		return indexOf(partition(base::begin(), base::end(), pred));
 	}
 
+	using PartitionResult
+			= std::pair<typename base::size_type, std::pair<typename base::size_type, typename base::size_type>>;
+
+	template<typename Pred1, typename Pred2>
+	PartitionResult
+	partition(Pred1 pred1, Pred2 pred2)
+	{
+		auto boundary1 = partition(base::begin(), base::end(), pred1);
+		auto begin2 = partition(base::begin(), boundary1, std::not_fn(pred2));
+		auto end2 = partition(boundary1, base::end(), pred2);
+		return {indexOf(boundary1), {indexOf(begin2), indexOf(end2)}};
+	}
+
 protected:
 	static constexpr auto npos = static_cast<size_t>(-1);
 	friend InstanceProxy;
-- 
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