How do I discard changes for a file in Git Gui?

Often when using Git Gui I would like to reset/checkout a single file or just dismiss a hunk.

Is there a way to do this easily in Git Gui? If not, is there any particular reason that this feature is not available in Git Gui?

Solution

I know this way:

The changes must be unstaged
Go to Tools -> Add
Choose whatever name you'd like for your command, then in Command write
git checkout $REVISION -- $FILENAME
Select (left-click) the file you want to checkout, without staging
Choose from Tools the command you just created

The chosen file will be checked out to HEAD revision