DrawGrowIcon
For window types with a sizing region, DrawGrowIcon draws the "size box icon in the lower-right corner and the scroll bar region on the right and
bottom sides. The action taken depends upon the window type and whether or
not it is highlighted.
theWindow is a WindowPtr identifying the window to modify.
Notes: Use DrawGrowIcon after receiving an update or activate event for a window that contains a sizing box (e.g., window types documentProc and
zoomDocProc). For these types of windows, the grow icon is drawn in the
lower-right corner and the lines delimiting the scroll bar areas
are drawn 15 pixels in from the right and bottom edges.
Since the scroll bars of a document window are within the content region of
the window, they are your responsibility. After an active window is moved
or resized, they must be refreshed, typically via MoveControl, If theWindow is inactive (unhighlighted), the size icon will be drawn as
appropriate to indicate that it temporarily cannot be sized.