From 84fb663d6cce83805a93132b591f4627c3505f39 Mon Sep 17 00:00:00 2001
From: sfan5 <sfan5@live.de>
Date: Sat, 17 Jun 2023 18:05:54 +0200
Subject: [PATCH] Add VoxelArea::intersect()

---
 src/unittest/test_voxelarea.cpp | 16 ++++++++++++++++
 src/voxel.h                     | 25 +++++++++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/src/unittest/test_voxelarea.cpp b/src/unittest/test_voxelarea.cpp
index a79c9778e..386fe499c 100644
--- a/src/unittest/test_voxelarea.cpp
+++ b/src/unittest/test_voxelarea.cpp
@@ -38,6 +38,7 @@ public:
 	void test_equal();
 	void test_plus();
 	void test_minor();
+	void test_intersect();
 	void test_index_xyz_all_pos();
 	void test_index_xyz_x_neg();
 	void test_index_xyz_y_neg();
@@ -74,6 +75,7 @@ void TestVoxelArea::runTests(IGameDef *gamedef)
 	TEST(test_equal);
 	TEST(test_plus);
 	TEST(test_minor);
+	TEST(test_intersect);
 	TEST(test_index_xyz_all_pos);
 	TEST(test_index_xyz_x_neg);
 	TEST(test_index_xyz_y_neg);
@@ -210,6 +212,20 @@ void TestVoxelArea::test_minor()
 			VoxelArea(v3s16(-10, -10, -45), v3s16(100, 100, 65)));
 }
 
+void TestVoxelArea::test_intersect()
+{
+	VoxelArea v1({-10, -10, -10}, {10, 10, 10});
+	VoxelArea v2({1, 2, 3}, {4, 5, 6});
+	VoxelArea v3({11, 11, 11}, {11, 11, 11});
+	VoxelArea v4({-11, -2, -10}, {10, 2, 11});
+	UASSERT(v2.intersect(v1) == v2);
+	UASSERT(v1.intersect(v2) == v2.intersect(v1));
+	UASSERT(v1.intersect(v3).hasEmptyExtent());
+	UASSERT(v3.intersect(v1) == v1.intersect(v3));
+	UASSERT(v1.intersect(v4) ==
+			VoxelArea({-10, -2, -10}, {10, 2, 10}));
+}
+
 void TestVoxelArea::test_index_xyz_all_pos()
 {
 	VoxelArea v1;
diff --git a/src/voxel.h b/src/voxel.h
index 16540e595..7a36b10bf 100644
--- a/src/voxel.h
+++ b/src/voxel.h
@@ -183,6 +183,31 @@ public:
 		return {MinEdge-off, MaxEdge-off};
 	}
 
+	/*
+		Returns the intersection of this area and `a`.
+	*/
+	VoxelArea intersect(const VoxelArea &a) const
+	{
+		// This is an example of an operation that would be simpler with
+		// non-inclusive edges, but oh well.
+		VoxelArea ret;
+
+		if (a.MaxEdge.X < MinEdge.X || a.MinEdge.X > MaxEdge.X)
+			return VoxelArea();
+		if (a.MaxEdge.Y < MinEdge.Y || a.MinEdge.Y > MaxEdge.Y)
+			return VoxelArea();
+		if (a.MaxEdge.Z < MinEdge.Z || a.MinEdge.Z > MaxEdge.Z)
+			return VoxelArea();
+		ret.MinEdge.X = std::max(a.MinEdge.X, MinEdge.X);
+		ret.MaxEdge.X = std::min(a.MaxEdge.X, MaxEdge.X);
+		ret.MinEdge.Y = std::max(a.MinEdge.Y, MinEdge.Y);
+		ret.MaxEdge.Y = std::min(a.MaxEdge.Y, MaxEdge.Y);
+		ret.MinEdge.Z = std::max(a.MinEdge.Z, MinEdge.Z);
+		ret.MaxEdge.Z = std::min(a.MaxEdge.Z, MaxEdge.Z);
+
+		return ret;
+	}
+
 	/*
 		Returns 0-6 non-overlapping areas that can be added to
 		a to make up this area.