>Psychtoolbox>PsychRects

rect=AlignRect(rect,fixedRect,side1,[side2])

Moves rect to align its center/top/bottom/left/right with the
corresponding edge(s)/point of fixedRect. Does “side1” and then “side2”.
The legal values for side1 and side2 are ‘center’, ‘left’, ‘right’,
‘top’, and ‘bottom’.
r=AlignRect(r,screenRect,’center’,’top’);
For backward compatibility, also accepts 1,2,3,4,5. You may use the
pre-defined constants RectLeft,RectRight,RectTop,RectBottom, but there is
no named constant for centering.
Also see PsychRects.