help ,  i want to crop image , like gallery–>edit–>crop.  i can see  a rectangel over the image , the rectangel has several points.  when i drag it ,  it can move and resize .  i want to  implement this function, and crop image .  can anyone help me ? thanks.

now , i  intend to use cairo and Image Util , cairo to draw rectangel, and  image util to crop.   i donnot know whether it is ok .