ProfitPress Mega CDROM2 …eeware (MSDOS)(1992)(Eng)/ProfitPress-MegaCDROM2.B6I/PROG/PASCAL/TOTDOC.ZIP/CHAPT18.TXT

Text File | 1991-02-10 | 15.1 KB | 334 lines

                                                                       Extending
                                                                         Windows



         "The success hasn't gone to our price."          Peugeot Motor Company





         Earlier, in chapter 7: Using Windows (page 7-12) a template for
         stretchable windows was presented. This template illustrated how, with
         just a few procedures, you could build customized windows. In this
         chapter you will learn how to use OOP techniques to extend window
         objects, and gain even more flexibility. To illustrate the concepts,
         the StretchWinOBJ object will be extended to provide a generic object
         for scrolling virtual screens.



Window Object Structure

         Before trying to extend the window objects, you need to have an under-
         standing of how the window objects function. The table below describes
         the data declared in each window object.



                                       WinOBJ
                 Variable                         Description
           vBorder: tCoords     The (X1,Y1,X2,Y2) coordinates of the window
                                border.
           vOuter: tCoords      The (X1,Y1,X2,Y2) coordinates of the saved
                                screen area, i.e. window and shadow.
           vUnderneathPtr:      A pointer to the saved image overlaid by the
           pointer              window.
           vSavedSize: longint  The size, in bytes, of the saved area.
           vTitle: string       The window title.
           vBorderAttr          The window display attributes.
           vTitleAttr
           vBodyAttr
           vIconsAttr: byte
           vStyle:byte          The window style.
           vRemove: boolean     A boolean to indicate whether the window will
                                be removed when the object is Done.
           vCursX,vCursY,       The cursor settings at the time the window was
           vCursTop,            displayed.
           vCursBot: byte
           vOldWin: tByteCoords The window settings at the time the window was
                                displayed.
           vOldWinConfine:      A boolean to indicate whether window settings
           boolean              were active when the window was displayed.
           vMVisible: boolean   A boolean to indicate whether the mouse was
                                visible when the window was displayed.

18-2                                                       Extending the Toolkit

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                                       MoveWinOBJ
                 Variable                         Description


           vBoundary:tCoords    The (X1,Y1,X2,Y2) coordinates of the area in
                                which the window can be moved.
           vMoveKey: word       The key to press to invoke a manual (non-mouse)
                                move.
           vAllowMove:boolean   A boolean to indicate whether the user is
                                allowed to move the window.


                                       ScrollWinOBJ
                 Variable                         Description
           vScrollV:boolean;    A boolean to indicate whether the vertical
                                scroll bar is visible.
           vScrollH:boolean;    A boolean to indicate whether the horizontal
                                scroll bar is visible.




                                       StretchWinOBJ
                 Variable                         Description
           vZoomed:boolean      A boolean to indicate whether the window is
                                currently zoomed.
           vPreZoom:tCoords     The coordinates of the window border prior to
                                zooming.
           vMinWidth:byte       The minimum width of the window.
           vMinDepth:byte       The minimum depth of the window.
           vStretchKey:word     The key to press to invoke a manual (non-mouse)
                                stretch.
           vZoomKey:word        The key to press to invoke a manual (non-mouse)
                                zoom.
           vAllowStretch:       A boolean to indicate whether the user is
           boolean              allowed to stretch the window.
           vSmartStretch:       A boolean to indicate whether the window will
           boolean              be updated during a stretch operation.


         Note that the type tCoords is defined as follows:

                  tCoords = record
                     X1,Y1,X2,Y2: shortint;
                  end;


         By now, you should already know most of the window methods in the file
         TOTWIN.PAS. Review the declaration of all four windows objects for a
         complete list of the methods. From an object extension perspective, the
         following methods are important:

         constructor Init;

         Initializes the object.

Extending Windows                                                           18-3

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         procedure WinKey(var K:word; var X,Y: byte); VIRTUAL;

         WinKey is passed keystroke details as variable parameters. If the key-
         stroke is window specific, e.g. a click on the close icon, a zoom, a
         window stretch etc., the method will process the key and modify the
         relevant window characteristic. The value of K is then updated to indi-
         cate the type of activity, e.g. set to 602 to indicate that the window
         has been re-sized.

         procedure StretchRefresh; VIRTUAL;

         While the user is stretching the lower right window, the method Stret-
         chRefresh is continuously called. This is the mechanism for dynamically
         showing the user how the window will appear while it is being
         stretched. The method is only called if the boolean vSmartStretch is
         set to true. There are two important items to consider. Firstly, this
         method will only be called while the window settings are suspended, so
         any screen writing statements in the procedure must use the full-screen
         coordinate system. Secondly, this method must complete its display
         update very quickly. It will be called continuously during a stretch
         operation, and if the procedure takes too long, the user will notice a
         sluggish response.

         procedure Draw; VIRTUAL;

         Draw saves the contents of the portion of the screen which will be
         overlaid by the window, and then draws the window and shadow.

         destructor Done; VIRTUAL;

         Disposes of the window object memory, and removes the window (if it is
         still visible and the vRemove variable is set to true).


         If you extend any window object, you will probably modify most of these
         methods, since they control the window display and input processing
         routines.



Extending StretchWinOBJ

         To illustrate the principles of window extension, a new window object
         for displaying and scrolling virtual screens will be created. You may
         recall that a virtual screen is a screen which has all the properties
         of the physical screen, but is not visible. A virtual screen can be up
         to 255 characters wide and 255 lines deep - quite a screen! The Screen-
         OBJ method PartDisplay can be used to transfer a portion of the virtual
         screen to the visible screen.



18-4                                                       Extending the Toolkit

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         The first task in designing the new object is to decide what additional
         data will be needed. Obviously, the object will need to know the
         address of the virtual screen, i.e. a pointer to a ScreenOBJ instance.
         Two additional variables will be required to keep track of which part
         of the virtual screen is on display. In other words, the coordinates of
         the top-left corner of the visible part of the virtual screen. To make
         sure that the user doesn't scroll beyond the bottom-edge or past the
         right-edge of the virtual screen, the object will need to know the
         width and depth of the virtual screen. The preliminary object declara-
         tion might therefore be as follows:

         VirtualWinOBJ = object (StretchWinOBJ)
            vScreen: ScreenPtr;
            vTopLine: integer;   {line number of first visible line}
            vFirstChar: integer; {number of left-most visible character}
            vScreenWidth: byte;
            vScreenDepth: byte;
            {Methods...}
            constructor Init;
            procedure   AssignVirtualScreen(var Scr:ScreenOBJ);
            destructor  Done;                                    VIRTUAL;
         end; {VirtualWinOBJ}


         So far so good, but the method Draw, inherited from StretchWinOBJ, will
         only draw the window border and then clear the central area of the
         window. VirtualWinOBJ needs to have its own Draw method. This method
         will first call StretchWinOBJ.Draw to display the basic window, and
         will then draw the visible part of the virtual window by calling the
         virtual window's method PartDisplay. The new Draw method will then need
         to update the vertical and horizontal scroll bars to accurately reflect
         which portion of the virtual screen is visible.

         The inherited methods DrawHorizbar and DrawVertBar can be used to draw
         the scroll bars. These methods are passed two longint parameters repre-
         senting the current position and maximum possible position. For exam-
         ple, the following statements will correctly update the StretchWinOBJ
         scroll bars:

                  DrawHorizBar(vFirstChar,vScreenWidth);
                  DrawVertBar(vTopLine,vScreenDepth

         Since the virtual screen method PartDisplay is mega-fast, we should be
         able to refresh the window display during a stretch. This is achieved
         by adding the method StretchRefresh. All StretchRefresh needs to do is
         restore the visible portion of the virtual screen, and paint any area
         of the window which may be beyond the virtual window boundary.



Extending Windows                                                           18-5

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         The inherit WinKey method will only process keystrokes which close,
         move or stretch the window. StretchWinOBJ needs to have its own WinKey
         method which calls the inherited one, and then processes any of the
         scrolling keys like End, Home, PgUp, PgDn, etc. as well as any mouse
         clicks on the scroll bars.

         Finally, a Go method could be added. This method would continuously get
         user input and call WinKey until the user escaped or clicked on the
         close icon.

         After all these enhancements, the declaration of the full-blown Virtu-
         alWinOBJ would be as follows:

         VirtualWinOBJ = object (StretchWinOBJ)
            vScreen: ScreenPtr;
            vTopLine: integer;
            vFirstChar: integer;
            vScreenWidth: byte;
            vScreenDepth: byte;
            {Methods...}
            constructor Init;
            procedure   SetScreenXY(X,Y:byte);
            procedure   AssignVirtualScreen(var Scr:ScreenOBJ);
            procedure   RefreshWindow;
            procedure   ScrollDown;
            procedure   ScrollUp;
            procedure   ScrollLeft;
            procedure   ScrollRight;
            procedure   ScrollTop;
            procedure   ScrollBottom;
            procedure   ScrollHome;
            procedure   ScrollEnd;
            procedure   ScrollJump(Vert:boolean; X,Y:byte);
            procedure   ScrollPgUp;
            procedure   ScrollPgDn;
            procedure   Go;
            procedure   StretchRefresh;                       VIRTUAL;
            procedure   Winkey(var K:word;var X,Y:byte);      VIRTUAL;
            procedure   Draw;                                 VIRTUAL;
            destructor  Done;                                 VIRTUAL;
         end; {VirtualWinOBJ}


         The on-disk unit file EXTWIN.PAS contains the complete implementation
         of the VirtualWinOBJ method. You might print out this unit and review
         the detailed statements to gain a thorough understanding of how Virtu-
         alWinOBJ functions. Since all the work has been done for you, you might
         consider creating a descendant of VirtualWinOBJ which includes on-line
         help, printing, etc.




18-6                                                       Extending the Toolkit

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Using VirtualWinOBJ

         Using the new VirtualWinOBJ object is a snap. The demo program EXT-
         DEM4.PAS, listed below, shows how the object could be used to display
         the good 'ole ASCII table. Figure 18.1 shows the display generated by
         the demo program.



         Program ExtendedDemoFour;
         {EXTDEM4}

         Uses DOS,CRT,
              totINPUT, totFAST, totSTR, extWIN;

         var
            ASCIIdata: ScreenOBJ;
            AscWin: VirtualWinOBJ;

         procedure BuildASCIIscreen;
         {creates the virtual screen}
         var
            I,J : integer;
            Str:string;
         begin
            with ASCIIdata do
            begin
               Init;
               Create(65,32,71);
               for I := 0 to 31 do
               begin
                  Str := '';
                  for J := 0 to 7 do
                  begin
                     Str := Str+' '+
                            padright(inttostr(I+32*J),3,'0')+
                            ' '+char(I+32*J)+' ';
                     if J <> 7 then
                        Str := Str + '│';
                  end;
                  WritePlain(1,succ(I),Str);
               end;
               for J := 0 to 7 do
                   Attrib(6+J*8,1,6+J*8,32,78);
            end;
         end; {BuildASCIIscreen}

         begin
            Screen.Clear(white,'░'); {paint the screen}
            Key.SetFast;
            BuildASCIIscreen;
            with AscWin do



Extending Windows                                                           18-7

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            begin
               Init;
               SetTitle(' ASCII Table ');
               AssignVirtualScreen(ASCIIdata);
               Go;
               ASCIIdata.Done;
               Done;
            end;
         end.



Figure 18.1                                                             [SCREEN]
Using
VirtualWinOBJ