// Calculate the position of the four corners in world space by applying
// The world matrix to the four corners in object space (0, 0, width, height)
Vector2 tl = Vector2.Transform(Vector2.Zero, matrix);
Vector2 tr = Vector2.Transform(new Vector2(extents.x, 0), matrix);
Vector2 bl = Vector2.Transform(new Vector2(0, extents.y), matrix);
Vector2 br = Vector2.Transform(extents, matrix);
// Find the minimum and maximum "corners" based on the ones above
float minX = Min(tl.X, Min(tr.X, Min(bl.X, br.X)));
float maxX = Max(tl.X, Max(tr.X, Max(bl.X, br.X)));
float minY = Min(tl.Y, Min(tr.Y, Min(bl.Y, br.Y)));
float maxY = Max(tl.Y, Max(tr.Y, Max(bl.Y, br.Y)));
Vector2 min = new Vector2(minX, minY);
Vector2 max = new Vector2(maxX, maxY);
// And create the AABB
RectangleF aabb = new RectangleF(min, max - min);