MultiPolygon::centroid()の実装(#1186) (#1190)

Author: Ogame3334

Siv3D/include/Siv3D/MultiPolygon.hpp

@@ -417,6 +417,9 @@ namespace s3d
 		[[nodiscard]]
 		double perimeter() const noexcept;
 
+		[[nodiscard]]
+		Vec2 centroid() const;
+
 		[[nodiscard]]
 		RectF computeBoundingRect() const noexcept;
 

Siv3D/src/Siv3D/MultiPolygon/SivMultiPolygon.cpp

@@ -330,6 +330,26 @@ namespace s3d
 		return total;
 	}
 
+	Vec2 MultiPolygon::centroid() const
+	{
+		if (m_data.empty())
+		{
+			return Vec2{ 0, 0 };
+		}
+		
+		Vec2 weightedCoordsTotal{ 0, 0 };
+		double areaTotal = 0.0;
+		
+		for (const auto& polygon : m_data)
+		{
+			const double polygonArea = polygon.area();
+			weightedCoordsTotal += polygonArea * polygon.centroid();
+			areaTotal += polygonArea;
+		}
+		
+		return weightedCoordsTotal / areaTotal;
+	}
+
 	RectF MultiPolygon::computeBoundingRect() const noexcept
 	{
 		if (isEmpty())