DropWidth of Column Combo as in-place editor

I am using TAdvColumnGrids, with TColumnComboBoxes as in-place editors. In a number of place, I need the combo to display data from two columns, and have built a function to resize the columns dynamically to fit the text. However, there are some instances in which I need to limit the combo DropWidth to prevent it extending off the screen. 

How can I obtain the left coordinate of the column of a scrolled grid at runtime with respect to the form?

Thanks, I resolved it.