AssetRipper_AssetRipper/Source/AssetRipper.Numerics/GeometricMath.cs

namespace AssetRipper.Numerics
{
	public static class GeometricMath
	{
		private const float kEpsilon = 0.00001F;

		/// <summary>
		/// Angle increase when 2nd line is moving in clockwise direction
		/// </summary>
		/// <returns>Angle in degrees</returns>
		public static float AngleFrom3Points(Vector2 point1, Vector2 point2, Vector2 point3)
		{
			float transformedP1X = point1.X - point2.X;
			float transformedP1Y = point1.Y - point2.Y;
			float transformedP2X = point3.X - point2.X;
			float transformedP2Y = point3.Y - point2.Y;

			double angleToP1 = Math.Atan2(transformedP1Y, transformedP1X);
			double angleToP2 = Math.Atan2(transformedP2Y, transformedP2X);
			
			double angle = angleToP1 - angleToP2;
			if (angle < 0)
			{
				angle += 2 * Math.PI;
			}

			return (float)(360.0 * angle / (2.0 * Math.PI));
		}
	}
}