<* PRAGMA LL *>
<* PRAGMA SUBTYPE *>

Views may be added or deleted under program control or by appropriate gestures in the scrollbar: Option Left click adds a new view after the view in which the user clicked. Option Right click removes the view (unless, of course, it would leave the viewport with zero views!).

INTERFACE ViewportVBT;

IMPORT Axis, HVSplit, Rect, Shadow, VBT;

TYPE
  <* SUBTYPE T <: MultiFilter.T *>
  T <: Public;
  Public = HVSplit.T OBJECT
           METHODS
             <* LL <= VBT.mu *>
             init (ch             : VBT.T;
                   axis           : Axis.T   := Axis.T.Ver;
                   shadow         : Shadow.T := NIL;
                   step           : CARDINAL := 10;
                   scrollStyle := ScrollStyle.AlaViewport;
                   shapeStyle  := ShapeStyle.Unrelated;
                   multiView: BOOLEAN := TRUE): T;
           END;

The internal structure of a viewport is a rather complex collection of JoinedVBTs, HVSplits, ScrollerVBTs, and others. It depends on the options with which the viewport was created. Be sure to use the MultiFilter interface to get at the child.

TYPE
  View = INTEGER;

A viewport can be created with a number of different styles of scrollbars:

TYPE
  ScrollStyle =
    {HorAndVer,
     HorOnly,
     VerOnly,
     NoScroll,
     AlaViewport,
     Auto};

\begin{itemize}

\item HorAndVer puts a horizontal and vertical scrollbar on every view. In addition, nestled between the scrollbars in the southwest corner, there's a little ``reset'' button that moves the northwest corner of the child to the northwest corner of the view.

\item HorOnly places a scrollbar at the bottom.

\item VerOnly places a scrollbar at the left side.

\item NoScroll specifies that views will not have scrollbars.

\item AlaViewport specifies that there is a scrollbar in the same axis as the viewport. Thus, AlaViewport for a vertical viewport is equivalent to VerOnly.

\item Auto specifies that scrollbars appear only when the preferred size of the child exceeds the size of the viewport (in that dimension).

\end{itemize}

The location of the scrollbar is further controlled by the environment variable SCROLLBARMODEL; see the VBTKitEnv interface.

There are two possible shape-relationships between a viewport and its child:

TYPE ShapeStyle = {Unrelated, Related};

Related makes the child's shape equal to the viewport's shape in the non-axis direction of the viewport. In the viewport's axis direction, the child's preferred shape is used. For example, the width of the child in a Vertical viewport is the width of the viewport.

\subsubsection{Panning the contents}

PROCEDURE ScrollTo (         v    : T;
                    READONLY r    : Rect.T;
                             view : View     := 0;
                             force: BOOLEAN  := TRUE);
<* LL = VBT.mu *>

Scroll the viewport v so that rectangle r is visible in view view. Rectangle r will be roughly centered within v, but if r is too big to be seen entirely, its northwest corner will be made visible. If force is FALSE and r is already entirely visible, this procedure is a no-op.

PROCEDURE Normalize (v: T; w: VBT.T; view: View := 0);
<* LL = VBT.mu *>

If the domain of w is non-empty and it's entirely visible, do nothing. Otherwise, do a ScrollTo to w's domain in view view.

      ScrollTo(v, VBT.Domain(w), FALSE)
   

\subsubsection{Multiple views}

PROCEDURE AddView (v: T; pred: View := -1; split := TRUE):
  View;
<* LL = VBT.mu *>

Add another view after the view pred (-1 means add as the first view) of the child. If split is TRUE, then the new view and the view pred will occupy the area previously occupied by the view pred. The area of all other views will be unchanged. The value returned is an internal ID for the view. This value may be reused after the view has been removed.

PROCEDURE RemoveView (v: T; view: View);
<* LL = VBT.mu *>

Remove the view view from v's child. The ID for the initial view created by the init method is 0.

END ViewportVBT.