RectanglePacking.cs

public static void PackRectanglesModify(List<PackedRectangle> rectangles)
{
	rectangles.Sort
	(
		Comparing.CreateComparer<PackedRectangle, double>
		(
			rect => rect.Rectangle.Size.X * rect.Rectangle.Size.Y
		)
	);
	rectangles.Reverse();
	var possibleSpots = new List<AARectangle>();
	possibleSpots.Add
	(
		new AARectangle
		(
			new Vector2d(0, 0),
			new Vector2d(double.MaxValue, double.MaxValue)
		)
	);
	var placedRectangles = new List<AARectangle>();
	foreach (var rect in rectangles)
	{
		possibleSpots.Sort
		(
			Comparing.CreateComparer<AARectangle, double>
			(spot =>
				Math.Max
				(
					spot.Position.X + rect.Rectangle.Size.X,
					spot.Position.Y + rect.Rectangle.Size.Y
				)
			)
		);
		var bestSpot = possibleSpots.First
		(spot =>
			spot.Size.X >= rect.Rectangle.Size.X &&
			spot.Size.Y >= rect.Rectangle.Size.Y
		);
		rect.Rectangle.Position = bestSpot.Position;
		placedRectangles.Add(rect.Rectangle);
		possibleSpots.Remove(bestSpot);
		var toRemove = new List<AARectangle>();
		foreach (var spot in possibleSpots)
		{
			FitRectangle(spot, rect.Rectangle);
			if (spot.Size.X <= 0 || spot.Size.Y <= 0)
			{
				toRemove.Add(spot);
			}
		}
		toRemove.ForEach(x => possibleSpots.Remove(x));
		possibleSpots.Add
		(
			new AARectangle
			(
				rect.Rectangle.Position.X + rect.Rectangle.Size.X,
				rect.Rectangle.Position.Y,
				bestSpot.Size.X - rect.Rectangle.Size.X,
				bestSpot.Size.Y
			)
		);
		possibleSpots.Add
		(
			new AARectangle
			(
				rect.Rectangle.Position.X,
				rect.Rectangle.Position.Y + rect.Rectangle.Size.Y,
				bestSpot.Size.X,
				bestSpot.Size.Y - rect.Rectangle.Size.Y
			)
		);
	}
}

private static void FitRectangle(AARectangle toFit, AARectangle other)
{
	if (other.Position.X >= toFit.Position.X &&
		IntervalsIntersect
		(
			toFit.Position.Y,
			toFit.Position.Y + toFit.Size.Y,
			other.Position.Y,
			other.Position.Y + other.Size.Y
		))
	{
		toFit.Size.X = Math.Min(other.Position.X - toFit.Position.X, toFit.Size.X);
	}
	if (other.Position.Y >= toFit.Position.Y &&
		IntervalsIntersect
		(
			toFit.Position.X,
			toFit.Position.X + toFit.Size.X,
			other.Position.X,
			other.Position.X + other.Size.X
		))
	{
		toFit.Size.Y = Math.Min(other.Position.Y - toFit.Position.Y, toFit.Size.Y);
	}
}

private static bool IntervalsIntersect(double x1, double y1, double x2, double y2)
{
	return Math.Min(y1 - x2, y2 - x1) > 0;
}