Xcode将图像保存为特定形状

In Swift or Objective-C does anyone know how to let the user take a picture (either from album or camera) and save it to a specific design. For example, I have seen how Instagram allows a user to set their profile picture and it appears as a circle. How does one save it to a circle, I am trying to use a triangle, any suggestions?In Swift or Objective-C does anyone know how to