Damage(3U)						    InterViews Reference Manual 						Damage(3U)

NAME

       Damage - repairs damaged graphics

SYNOPSIS

       #include <Unidraw/Graphic/damage.h>

DESCRIPTION

       Damage  objects	store  damaged	areas of a graphic for subsequent incremental repair.  Areas of a graphic are "damaged" if they need to be
       redrawn for any reason, e.g., if their state has been modified or if under/overlapping graphics change their  appearance.   Damage  objects
       try  to	minimize  the amount of redrawing needed to repair a graphic.  They are most useful when the graphic is complicated enough that it
       would be undesirable to redraw the entire canvas when the graphic is modified.  Damage objects do not eliminate the need  for  an  interac-
       tor's Redraw member function, though they could be used to implement it.

PUBLIC OPERATIONS

       Damage(Canvas* = nil, Painter* = nil, Graphic* = nil)
	      Create  a new Damage object for a graphic on the given canvas.  The painter is used to erase damaged areas using its ClearRect func-
	      tion prior to redrawing them.

       virtual void Incur(Graphic*)
       virtual void Incur(BoxObj&)
       virtual void Incur(
	   Coord left, Coord bottom, Coord right, Coord top
       )
	      Notify the damage object that a rectangular area has been damaged, either by passing the graphic that contributed the  area  or  the
	      area itself.

       virtual void Added(Graphic*)
	      Notify  the  damage object that the given graphic was appended (not inserted) to the graphic but never drawn.  The damage object can
	      thus be responsible for drawing newly added graphics as well.

       virtual void Repair()
	      Repair all damage incurred since the last Repair (or since the damage object was created if this is the first Repair).

       virtual void Reset()
	      Reset the damage object.	Any damage incurred is lost.

       virtual boolean Incurred()
	      Returns true if any damage has been incurred.

       void SetCanvas(Canvas*)
       void SetPainter(Painter*)
       void SetGraphic(Graphic*)

       Canvas* GetCanvas()
       Painter* GetPainter()
       Graphic* GetGraphic()
	      Set and get attributes of the damage object.

PROTECTED OPERATIONS

       int Area(BoxObj&)
	      A helper function that returns the area in square pixels occupied by the given BoxObj.

       virtual void DrawAreas()
       virtual void DrawAdditions()
	      Explicitly draw the areas of incurred and added damage, respectively.

       virtual void Merge(BoxObj&)
	      Merge the given BoxObj into the list of incur-damaged areas, coalescing it into an existing area if the  number  of  non-overlapping
	      areas exceeds 2.

       void FirstArea(Iterator&)
       void FirstAddition(Iterator&)
       void Next(Iterator&)
       boolean Done(Iterator)
       BoxObj* GetArea(Iterator)
       Graphic* GetAddition(Iterator)
	      Operations  for  iterating  over	the  lists  of	damaged areas (represented with BoxObj objects) and added Graphics.  FirstArea and
	      FirstAddition initialize the iterator to point to the first item on the corresponding list, Next advances  the  iterator,  and  Done
	      returns  true  if the iterator points beyond the end of the list.  GetArea and GetAddition return the BoxObj or Graphic to which the
	      iterator points.

       UList* Elem(Iterator)
	      A helper function for returning the UList to which an iterator points.  The _areas protected member is a UList that stores the  list
	      of damaged areas, and the _additions protected stores the list of added graphics.

       void DeleteArea(BoxObj*)
       void DeleteAreas()
	      DeleteArea  is  a  helper  function for deleting the storage associated with a damaged area, including the area itself and the UList
	      element.	DeleteAreas is a helper function that deletes the list of damaged areas.

SEE ALSO

       Canvas(3I), Graphic(3U), Iterator(3U), Painter(3I), UList(3U), geomobjs(3U)

Unidraw 							  30 January 1991							Damage(3U)