Creating a Proportional Scroll Box

Your application should call the function SetControlViewSize to support proportional scroll boxes. If the user selects the systemwide Appearance preference for "Smart Scrolling" and your application doesn't call SetControlViewSize , your application displays the traditional square scroll boxes.

To support a proportional scroll box, simply pass the size of the view area--in terms of whatever units the scroll bar uses--to SetControlViewSize . The system automatically handles resizing the scroll box, once your application supplies this information. Listing 1-1 shows some typical code for setting a scroll bar according to a TextEdit handle, which includes making the scroll box proportional.

Listing 1-1 Adjusting a scroll bar to the viewable text



 
static pascal void AdjustScrollBarToText

    (TEHandle teh, ControlHandle scrollBar)

{

    // get the values needed to reflect the state of the TEHandle

    short nLines    = (**teh).nLines; // number of lines in doc.

    long totalHeight= TEGetHeight (nLines, 1, teh); // total doc. height

    Rect viewRect   = (**teh).viewRect; // visible area of doc.

    Rect destRect   = (**teh).destRect; // total area of doc.

    short viewHeight= viewRect.bottom - viewRect.top; // vis. doc. height



    // set the min, max, and current value of the scroll bar

    SetControl32BitMinimum (scrollBar, 1);

    SetControl32BitMaximum (scrollBar, totalHeight - viewHeight);

    SetControl32BitValue (scrollBar, viewRect.top - destRect.top);



    // set the scroll bar view size to create a proportional scroll box

    SetControlViewSize (scrollBar, viewHeight);

}