add Area.Union()

area.go

@@ -47,3 +47,23 @@ func (a *Area) Intersects(a2 *Area) bool {
 	}
 	return false
 }
+
+func (a *Area) Union(a2 *Area) *Area {
+	if !a.Intersects(a2) {
+		// no union possible
+		return nil
+	}
+
+	return &Area{
+		Pos1: NewPos(
+			max(a.Pos1.X(), a2.Pos1.X()),
+			max(a.Pos1.Y(), a2.Pos1.Y()),
+			max(a.Pos1.Z(), a2.Pos1.Z()),
+		),
+		Pos2: NewPos(
+			min(a.Pos2.X(), a2.Pos2.X()),
+			min(a.Pos2.Y(), a2.Pos2.Y()),
+			min(a.Pos2.Z(), a2.Pos2.Z()),
+		),
+	}
+}

area_test.go

@@ -32,3 +32,58 @@ func TestArea(t *testing.T) {
 	assert.False(t, a2.Intersects(a))
 	assert.False(t, a.Intersects(a2))
 }
+
+func TestAreaUnion(t *testing.T) {
+	// simple area set
+	a1 := types.NewArea(
+		types.NewPos(0, 0, 0),
+		types.NewPos(10, 10, 10),
+	)
+	a2 := types.NewArea(
+		types.NewPos(0, 0, 0),
+		types.NewPos(5, 5, 5),
+	)
+	u := a1.Union(a2)
+	assert.Equal(t, types.NewPos(0, 0, 0), u.Pos1)
+	assert.Equal(t, types.NewPos(5, 5, 5), u.Pos2)
+
+	// area with offset
+	a1 = types.NewArea(
+		types.NewPos(2, 2, 2),
+		types.NewPos(10, 10, 10),
+	)
+	a2 = types.NewArea(
+		types.NewPos(0, 0, 0),
+		types.NewPos(5, 6, 7),
+	)
+	u = a1.Union(a2)
+	assert.Equal(t, types.NewPos(2, 2, 2), u.Pos1)
+	assert.Equal(t, types.NewPos(5, 6, 7), u.Pos2)
+
+	// non-intersecting area
+	a1 = types.NewArea(
+		types.NewPos(2, 2, 2),
+		types.NewPos(10, 10, 10),
+	)
+	a2 = types.NewArea(
+		types.NewPos(11, 11, 11),
+		types.NewPos(13, 13, 13),
+	)
+	u = a1.Union(a2)
+	assert.Nil(t, u)
+
+	// 1-node intersects
+	a1 = types.NewArea(
+		types.NewPos(2, 2, 2),
+		types.NewPos(2, 2, 2),
+	)
+	a2 = types.NewArea(
+		types.NewPos(2, 2, 2),
+		types.NewPos(2, 2, 2),
+	)
+	u = a1.Union(a2)
+	assert.Equal(t, types.NewPos(2, 2, 2), u.Pos1)
+	assert.Equal(t, types.NewPos(2, 2, 2), u.Pos2)
+	assert.Equal(t, 1, u.Volume())
+	assert.Equal(t, types.NewPos(1, 1, 1), u.Size())
+}