how to know the panel on the above or below the combo input

[dailyblog]

hi,how to get the position of panel of combo. I want to know whether the panel is on the above or below the combo input before panel shows.
I want to add animation to combo panel when panel showing or hiding. When panel is on the above of the combo input,the animation goes from bottom to top. When panel on the below of the combo panel,the animation goes from top to bottom.so i what to know the position of the panel to combo input before showing or hiding.