These properties tell you the dimensions of the visible portion of a form. They're really only relevant when the form has scrollbars.
nVisibleHeight = frmForm.ViewPortHeight
nVisibleWidth = frmForm.ViewPortWidthWhen a form has scrollbars, some portion of it is hidden. (We almost said "may be hidden," but the way scrollbars work, they only appear if a portion of the form is actually hidden.) These two properties let you know the size of the part of the form the user can see.
IF This.ViewPortWidth > nSomeMagicValue
* There's enough room to do something special
This.oleGreatPicture.Visible = .T.
ENDIF