Copyright (C) 1992, Digital Equipment Corporation                         
 All rights reserved.                                                      
 See the file COPYRIGHT for a full description.                            
 Last modified on Fri Jun 11 22:00:14 PDT 1993 by meehan 
      modified on Thu Jan 28 14:03:14 PST 1993 by mhb    
      modified on Wed Jan 13 09:10:53 PST 1993 by steveg 
      modified on Tue Jun 16 13:08:22 PDT 1992 by muller 
A ScaleFilter is a multi-filter whose child's screentype is the same as the parent's except that the resolution is scaled.

INTERFACE ScaleFilter;


  <* SUBTYPE T <: MultiFilter.T *>
  T <: Public;
  Private <: VBT.T;
  Public = Private OBJECT
             <* LL.sup <= VBT.mu *>
             init (ch: VBT.T): T
The call v.init(ch) initializes v as a ScaleFilter with multi-child ch and with horizontal and vertical scale factors both equal to 1.0.

There are two ways you can use a ScaleFilter: Procedure Scale allows you to explicitly set a horizontal and vertical scale factor. Procedure AutoScale looks at the preferred size of the child and dynamically sets the scale factors such that the child's preferred size always fills its domain.

PROCEDURE Scale (v: T; hscale, vscale: REAL);
<* LL.sup = VBT.mu.v *>
Set v's horizontal and vertical scale factors to be hscale and vscale respectively, and mark v for redisplay.
 Thus, if the v has resolution of px and py horizontally
   and vertically, then the resolution of v's multi-child will
   be hscale*px and vscale*py.

Note that the locking level of Scale does not require the full share of VBT.mu. Therefore, it can be called from v's reshape or rescreen method, for example, since those methods are called with only v's share of VBT.mu locked. This fact is useful for the implementation of procedure AutoScale:

PROCEDURE AutoScale (v: T; keepAspectRatio := FALSE);
<* LL.sup = VBT.mu *>
Set v's scale factor such that the preferred size of v's child ch is scaled to fit into VBT.Domain(ch). If keepAspectRatio is TRUE, then ch is scaled by the same amount f both horizontally and vertically. The amount f is chosen so that the preferred size of ch just fits in the larger direction of v and fits fine in the other direction. In any event, v is marked for redisplay.
 The call to AutoScale has the effect of causing Scale to be
   called each time that v is reshaped. Thus, it is important that
   Scale have a locking level of VBT.mu.v rather than simply

PROCEDURE Get(v: T; VAR (* OUT *) hscale, vscale: REAL);
<* LL.sup = VBT.mu *>
Return v's current horizontal and vertical scale factors.
 If Scale was called more recently than AutoScale, then
   Get returns the values passed to Scale.  On the other hand, if
   AutoScale was called more recently, then Get will return
   values that reflect scaling for v's current domain. 

END ScaleFilter.