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MultiWindow DA
Volume Number:7
Issue Number:7
Column Tag:Pascal Procedures

Related Info: Menu Manager Resource Manager Window Mgr

Multi-Window/Menu DA

By Lincoln Stein, MD, Boston, MA

Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.

[Lincoln Stein, MD, is a Harvard Medical School Graduate. He is currently developing medical education software with the Decision Systems Group at Brigham and Women’s Hospital in Boston.]

Once Upon a Desktop

A long long time ago (well, only about two years, really) Macintosh applications and desk accessories were quite easy to tell apart. Applications supported multiple windows, owned all the menus in the menu bar, and ran one at a time. Desk accessories, in contrast, only had one window and a single menu if any. In partial compensation for these limitations, however, multiple desk accessories could run simultaneously with each other and the underlying application.

Things changed considerably with the advent of Multifinder. Now multiple applications can run simultaneously, nullifying desk accessories’ major advantage. The distinction will become even more murky with the advent of System 7, which promises to allow applications to be placed in the apple menu and to let desk accessories be launched from the desktop. The widespread predictions of the DA’s demise turned out to be premature, however. Indeed, desk accessories are proliferating as rapidly as ever and are reaching heights of sophistication that rival full-blown applications. At the same time that Multifinder has made applications more desk accessory-like, savvy developers have been making their desk accessories more and more application-like.

You’ve probably noticed that some commercial and public domain desk accessories are not content with the single window that imprisoned the classic desk accessories. These applications let you spawn new windows wantonly, a distinctly application-like thing to do. This article will show you how to repeat this multi-window trick. It will also show you how desk accessories can take over the entire menu bar in order to display Multiple menus, something that I haven’t seen done by any desk accessory, commercial or otherwise!

This article will not discuss the basics of how to write a desk accessory, which has been covered well in past articles (see MacTutor volumes II no. 4, II no. 5, II no. 6, and III no. 10).

A DA With a Difference

The example desk accessory, MultiDA, serves no useful function. It was written like this in order to keep the code simple. When the DA is invoked it takes over the menu bar and replaces the application’s menu bar with its own Apple, File, Edit and Windows menus. The DA allows you to open up an unlimited number of windows, type into a text edit field, cut and paste between windows, stack the windows up neatly, and close the windows. When the last window is closed, or when you choose “Quit” from the File menu, the desk accessory closes itself. If you select MultiDA from the apple menu when it is already open, it brings all its windows to the front. The desk accessory’s menus are switched in and out as appropriate so that there’s never any conflict between MultiDA’s menus and the application’s. MultiDA works under Unifinder and, surprisingly, under Multifinder as well (with a small caveat discussed later). Figure 1 shows MultiDA in action: notice that the Apple, File, Edit and Window menus all belong to the DA.

The code is written in Think Pascal. Unlike other development environments, Think lets you write desk accessories that use global variables and multiple segments. If you use a different development environment, you will have to make some changes to overcome these differences.

Figure 1. MultiDA.

Multiplying Menus

In principle it is as easy for a desk accessory to put up multiple menus as it is to put up a single menu. All the work of putting up and taking down a single menu occurs during activate and deactivate events. Whenever its window is activated, the desk accessory calls the Menu Manager routine InsertMenu to add its menu to the menu bar. Similarly, whenever the desk accessory window is deactivated, the DA calls DeleteMenu to remove its menu. In order to let the system know that the DA has put a menu up, the DA must store its menu’s ID in the dCtlMenu field of the driver’s driver control entry (this is a relocatable data structure created for each desk accessory when the DA is opened; see previous MacTutor articles for further information). Once this is done, the system refers all selections from that menu to the DA’s code.

Similarly, all the work of putting up multiple menus occurs during activate/deactivate events. In the source code, most of the fancy stuff occurs in the routines DoActivate, which handles both activate and deactivate events. The required steps are described in Inside Macintosh volume 1, pages 446-447. First the DA must save a copy of the application’s menu bar in its globals using the Menu Manager procedure GetMenuBar. Then it must clear the menu bar and add its own menu using ClearMenuBar followed by calls to InsertMenu. As before, it stores the ID of one of its menus into the dCtlMenu field of the driver control entry (any of the menu IDs will do for this purpose). Finally, and this is the key part, the desk accessory must save this same menu ID into the low memory global mBarEnable ($A20). This tells the system that the desk accessory now owns the entire menu bar directs the system to send all menu choices to the desk accessory rather than to the underlying application. Whenever the desk accessory window is deactivated, this process should be reversed. The menu bar should be cleared and the application’s menus put back using SetMenuBar with the previously stored copy. The mBarEnable global should then be cleared.

While the desk accessory’s menus are in the menu bar, the system handles all the tedious work of pulling down the menu and tracking the user’s selections. All the DA ever sees is an accMenu control call. When this call is received, the DA should examine the I/O parameter block (another desk accessory data structure: see Inside Macintosh for details) to determine the menu and item chosen: param[0] will contain the ID number of the menu chose, and param[1] will contain the item number of the selected menu item.

This is essentially all there is to giving a desk accessory multiple menus, and just a few details remain to be ironed out. The first detail is determining the IDs of the desk accessory’s menus. Usually, a menu is stored as a ‘MENU’ resource; its menu ID is usually identical to the resource ID number. The problem with desk accessories is that their resource numbers get shifted around by Font/DA Mover and by such utilities as Suitcase in order to avoid numbering conflicts with other desk accessories. In order to get around the problem of shifty resource ID’s, each resource used by the desk accessory is numbered as an “owned resource” (as described in the resource manager chapter of Inside Macintosh); The desk accessory’s own resource ID is mathematically combined with each owned resource’s “sub-ID” to form the true resource ID. While the ID number of the resources change each time the desk accessory’s ID changes, the sub-ID number never changes. The runtime resource ID can be derived from the driver’s reference number and the (constant) resource sub-ID using a “magic formula” which is given in the source code within the function GetResID.

When MultiDA initializes during its Open routine, it calculates its menu resource numbers using GetResID. It then reads the menus into memory one at a time (using GetMenu), and stores the returned menuHandles into a global array. It then stores the run-time ID into the MenuID field of the MenuHandle so that Menu Manager routines find the correct menu when required to. For convenience, the example DA stores the list of menu IDs in a global array so that the run-time IDs do not have to be calculated more than once.

A second bit of ironing concerns handling the command keys in DA-owned menus. Unfortunately the system does NOT handle menu command key selections for DA-owned menus. When the desk accessory receives a keydown event, it must check if the command key was held down, and if so, determine whether this corresponds to a menu selection. The natural thing to do would be to call the toolbox routine MenuKey in order to determine the corresponding menu and item number. Unfortunately, this call fails from within a desk accessory. The problem here is that MenuKey returns 0 if the associated menu item belongs to a desk accessory. Since a DA owns all the menus, MenuKey always returns 0. To circumvent this problem, you can use the routine DAMenuKey, given in the example program, to accomplish the same thing as MenuKey.

A third detail concerns the Apple menu. It’s nice for the desk accessory to put up an Apple menu so that the user can view the about box, use Multifinder, or choose other desk accessories. The problem here is that it isn’t very nice for an essentially parasitic desk accessory to open up other desk accessories without asking the underlying application’s permission. As far as I have been able to determine, only one popular application objects to this behavior; unfortunately that application happens to be Multifinder’s DA Handler. Apparently DA Handler counts the number of desk accessories opened while it is active. Whenever that count drops down to 0, DA Handler closes up its Multifinder partitition and quits. If several desk accessories are opened from within MultiDA, however, DA Handler can get confused and miscount. This can result in DA Handler exiting even though there are still desk accessories active. To avoid this problem, MultiDA checks to see if DA Handler is active, and if so, greys out the desk accessories items in the apple menu. It does not do this if Multifinder is not active or if the option key was held down when the DA was opened, forcing the desk accessory into the application’s heap.

The final detail is a merely cosmetic one. In a desk accessory with a single window and multiple menus, it is appropriate for the desk accessory to put up its menus when its window becomes active, and take down its menus when the window deactivates. However, when the DA has multiple windows, it isn’t necessary to mess with the menu bar on a deactivate event when all that’s happening is another one of the DA’s windows is becoming active. In order to avoid unnecessary menu bar flickering, MultiDA checks the event queue every time it receives a deactivate event. If it finds a pending activate event pertaining to one of its other windows, it leaves the menu bar as is.

Spawning Windows

Multiple desk accessory windows are slightly easier to implement than multiple menus. Opening desk accessory windows is easy: all you do is call NewWindow (or GetNewWindow) and store the DA’s driver reference number in the windowKind field of the newly-created window. This tells the system that the newly-opened window belongs to the desk accessory. This is demonstrated in the routine OpenAWindow in the example code.

The dCtlWindow field of the desk accessory’s driver control entry is supposed to point to the desk accessory’s window. When the DA has multiple windows, this field should point to the topmost DA window. A good time to update this field is when a window becomes active. In the example code, the routine DoActivate, in addition to swapping in the DA’s menus, places the activating window’s windowPtr into the dCtlWindow field.

Closing a window in a multi-window desk accessory is somewhat trickier. When the user clicks in any of the DA’s windows’ close boxes, the desk accessory receives a Close call. Ordinarily this means that the desk accessory should bank its fires and quit. However this is NOT what the user wants to happen when he’s only closing the topmost of several DA windows. The correct thing to do when a Close call is received is to determine how many DA windows are open. If more than one window is open, then the DA closes the topmost window (the pointer to which can be obtained from the dCtlWindow field) and informs the system that the DA didn’t close by returning a CloseErr (-24). If only one of the desk accessory’s windows is open, then the DA should go ahead and close up (it can, if it wishes, put up an “Are you sure?” alert and allow the user to change his mind).

There is one circumstance, however, in which the DA has no choice about whether to close. This occurs when the underlying application is quitting or when the Mac is shutting down. To handle this case, MultiDA has the dNeedGoodbye bit set in its header. When the heap is about to be reinitialized, the system sends MultiDA a “goodbye kiss” call. This gives the DA a chance to close all its windows and clean up its data.

The other thing to be careful about when one of the desk accessory’s multiple windows is closed is to make sure that the dCtlWindow field of the device control entry always points to a valid window. The CloseAWindow routine in the example source code contains a subroutine called UpdateDCE. This routine runs through the DA’s windows and updates the device control entry to point to the currently topmost DA window immediately after a window is closed. Never leave a pointer to a disposed window in the dCtlWindow field! This field must always remain valid. It is no use waiting for an activate event to fix the dCtlWindow field, since the Mac may well crash long before an activate event has had a chance to occur.

What should a multi-window desk accessories do when the user chooses the already-open desk accessory from the Apple menu? When this happens, the desk accessory receives a second Open call. One option is to activate just the topmost window (the one stored in the dCtlWindow field of the driver control entry). I chose the alternative behavior of bringing all the desk accessory’s windows to the front using the ModifyWindows routine. This behavior, simulating as it does the Multifinder “layers” effect, seemed more in keeping with what people expect.

Most Multi-window desk accessories will want to store a list of their currently open windows in some sort of global array. This would let them, for example, keep a parallel array of associated data structures, or create and maintain a Windows menu that lists the open windows and lets the user bring them to the front selectively. To keep the code simple, I didn’t do this in the example DA. Instead, whenever I want to perform a repetitive action on all the windows, such as bringing them all forward, stacking them up nicely, or closing them all, I call a routine called ModifyWindows. This routine takes a procedure pointer as one of its parameters. It searches through the linked window list for each of the DA’s windows (which it recognizes by the windowKind field), and then calls the procedure pointer for each window in turn. While playing with this way of doing things, I realized that some operations, such as stacking the windows up, would look much nicer if the operation were performed starting at the furthest back window and working forwards. The elegant way to do this was to make ModifyWindows a recursive procedure; see the code for details.

Compiling the Example Code

To compile the desk accessory in from the listing that follows you need Think Pascal and access to MPW rez or ResEdit. You must first use MPW rez (or ResEdit) to create a resource file. Then set up a Think Pascal project with the build order shown in Figure 2. You must use the drvrRuntime library rather than the standard runtime library or you will get link errors! Set Think’s runtime options to use the resource file you created. Then set up the project type dialog as shown in Figure 3.

Figure 2. Build Order.

Figure 3. Project Type.

Compile the project as a desk accessory. This will create a suitcase-type file that can be installed with Font/DA mover, or used with Suitcase or Font/DA juggler.

Concluding Remarks

MultiDA demonstrates how to implement multiple windows and menus from within a desk accessory. With these techniques, and with Think Pascal’s support for global data and multiple segments in DA’s, who needs applications?

{File Multi DA.p}
{Example of a desk accessory with multiple windows and menus.}
{© 1990, Lincoln D. Stein}
unit MenuDA;


function Main (DCtlE: DCtlPtr;
      IOPB: ParmBlkPtr;
      driveCall: Integer): OSErr;


{Define all of the possible driver calls}
DriverOpen = 0;
DriverPrime = 1;
DriverControl = 2;
DriverStatus = 3;
DriverClose = 4;

OpenErr = -23;
CloseErr = -24;

{Offsets to resource IDs for main dialog and alert}
DlogID = 0;
AboutID = 0;

{Subitem resource numbers of our menus}
AppleMenu = 0;
AboutItem = 1;

FileMenu = 1;
NewWindowItem = 1;
CloseItem = 2;
QuitItem = 4;

EditMenu = 2;
undoItem = 1;
cutItem = 3;
copyItem = 4;
pasteItem = 5;
clearItem = 6;

WindowMenu = 3;
CleanupItem = 1;
BeepItem = 2;

{Dialog itemlist}
NewWindowButton = 1;
EraseButton = 2;
EditText = 3;

MenuBar = (DAMenus, AppMenus);

done: boolean;
SavedMenuList: handle;
MenuIDs: array[0..WindowMenu] of integer;
OurMenus: array[0..WindowMenu] of MenuHandle;
OurMenuBar: boolean;

DCE: DCtlPtr;
OurName: str255;
NumWindows: integer;
WindowCounter: integer;

{ ********************************************** }
{ ************Global Utility Functions********** }
{ ********************************************** }
{The actual resource IDs of our resources depends on our desk accessory’s 
run-time device control reference number (this gets switched around by 
Font/DA Mover and Suitcase.  The “owned resource” sub-ID never changes, 
however.  Use our dCtlRefNum to get the run-time ID of our resources}
function GetResID (SubID: integer): integer;
 GetResID := BOR($C000, SubID + (BSL((Abs(DCE^.dCtlRefNum) - 1), 5)));

{MenuKey does not work from within a desk accessory because the system 
does not respond correctly to the meta-keys used in DA menus. This procedure 
is a substitute for MenuKey that performs the function correctly. Given 
a character, this function will determine if it is a menu meta-character 
and returns the menu ID in the high order word and the item in the low 
order word just as MenuKey does.  Note that this code makes use of information 
stored in our globals, and is NOT directly transferable to other desk 
function DAMenuKey (cmd: char): longint;
 i, item: integer;
 key: char;
{Return a ‘0’ as default}
 DAMenuKey := 0;
{Capitalize lowercase letters}
 if (cmd >= ‘a’) & (cmd <= ‘z’) then
  cmd := Chr(Ord(cmd) - (Ord(‘a’) - Ord(‘A’)));

{Loop through each menu, looking for matches}
 for i := 0 to WindowMenu do

{If we find an enabled menu then examine each enabled item in turn until 
we find a matching command key.}
  if BTST(OurMenus[i]^^.enableFlags, 0) then
   for item := 1 to CountMItems(OurMenus[i]) do

    if BTST(OurMenus[i]^^.enableFlags,item) then
      GetItemCmd(OurMenus[i], item, key);
      if key <> Cmd then
       DAMenuKey := BOR(item,BSL(MenuIDs[i],16));

end; {of FUNCTION MyMenuKey}

{************ Menu Handling Routines **********}

{Fetch and install our menus, remembering the application’s menu bar 
for later switching. We return the menu ID of any of our menus for installation 
into the dCtlMenu field of the device control entry. It doesn’t matter 
exactly which of our menus we return.}
function InitMenus: integer;
 CurApName = $910; {Low memory global}
{Hard code the name of the desk accessory layer in multifinder.  Note 
that there is a non-breaking space between DA and Handler.}
 DALayer = ‘DAHandler’;
 i: integer;
 name: str255;
 for i := 0 to WindowMenu do
   MenuIDs[i] := GetResID(i);
   OurMenus[i] := GetMenu(MenuIDs[i]);
   OurMenus[i]^^.MenuID := MenuIDs[i];

 AddResMenu(OurMenus[AppleMenu], ‘DRVR’);
 InitMenus := MenuIDs[AppleMenu];

{If we’ve been loaded into DA Handler, then we dim out our desk accessories. 
This is done because DA Handler does not like desk accessories opening 
other desk accessories!}
 if StringPtr(CurApName)^ = DALayer then
  for i:=1 to CountMItems(OurMenus[AppleMenu]) do
    GetItem(OurMenus[AppleMenu], i, name);
    if name[1] = char($00) then
     DisableItem(OurMenus[AppleMenu], i);

{This procedure is called in order to make a copy of, and save, the current 
menu bar data structure. It is conceivable that it may be called twice 
in a row, so dispose of any previously saved menubars.}
procedure SaveMenuBar;
 if SavedMenuList <> nil then
 SavedMenuList := GetMenuBar;

procedure InsertDAMenus;
 i: integer;
 for i := 0 to WindowMenu do
  InsertMenu(OurMenus[i], 0);

{This procedure adjusts the menus periodically to allow for changes It 
would typically be used enabling and disabling menuitems, changing item 
names, etc. as appropriate for the DA’s state.}
procedure AdjustMenus;
 if NumWindows > 1 then
  enableItem(OurMenus[Filemenu], CloseItem)
  disableItem(OurMenus[FileMenu], CloseItem)

{This procedure installs our menubar when one of our windows becomes 
active. Pass it “DAMenus” to install our DA’s menubar. Pass it “AppMenus” 
to restore the application’s menubar.}
procedure SetMenu (which: MenuBar);
 mBarEnable: ^integer;

{FUNCTION OursIsActivating is used to determine if one of our windows 
is about to come to the top. If this is going to happen, then there is 
no use switching menus when one of our windows is deactivated. It calls 
EventAvail, looking for an activate event in one of our own windows.}
function OursIsActivating: boolean;
  Evt: eventRecord;
  kind: integer;
  OursIsActivating := false;
  if EventAvail(activMask, Evt) &
(BitAnd(Evt.modifiers,activeFlag)<>0) then
     kind := WindowPeek(Evt.message)^.windowkind;
      OursIsActivating := (kind = DCE^.dctlRefNum)

begin {PROCEDURE SetMenu}
 mBarEnable := Pointer($A20);
  {Install DA’s menubar if requested to and our menu bar isn’t there 
 if (which = DAMenus) then
   if not OurMenuBar then
     MBarEnable^ := DCE^.dctlMenu;
     OurMenuBar := true;
 else if not OursIsActivating then
   MBarEnable^ := 0;
   OurMenuBar := False;

{ ********* Window Handling Routines ********* }
{********************************************* }

{----------------ModifyWindows---------------- }
{PROCEDURE ModifyWindows is passed a procedure parameter. It loops through 
our windows performing the passed procedure on each of our windows, starting 
with the window passed in Start. By calling itself recursively, it performs 
the action on the bottom-most window first and the top-most window last. 
A neat trick! }
procedure ModifyWindows (Start: UNIV WindowPeek;
       procedure DoSomething (aW: Windowptr));
 if Start = nil then
 WindowCounter := 1;
 ModifyWindows(Start^.NextWindow, DoSomething);
 if Start^.windowKind = DCE^.dctlRefNum then
   WindowCounter := succ(WindowCounter)

{The following procedures are used in calls to the ModifyWindows procedure 
to do the same task to each of our windows in turn...}

{PROCEDURE CleanupProc stacks the windows in place one by one, using 
the WindowCounter global to keep track of which window we’re working 
procedure CleanupProc (theWind: windowptr);
 spacing = 10;
 vStart = 40;
 hStart = 5;
 MoveWindow(theWind, WindowCounter * spacing + hStart, WindowCounter 
* spacing + vStart, true);

procedure BringWindowForward (aW: Windowptr);

{FUNCTION OpenAWindow opens up a new window, stores our DA’s dCtlRefNum 
into its windowKind field so that the system knows it’s a DA’s window, 
and sets the title and initial location in an appropriate manner. We 
use the run-time name of our desk accessory to form the window title. 
We also bump up our window counter to keep track of how many windows 
are open. This would be a good place to store the windowptr into an array 
or linked list, in order to keep track of the windows more carefully.}
function OpenAWindow: Windowptr;
 aW: windowptr;
 WindowNo: str255;
 aW:= GetNewDialog(theID, nil, pointer(-1));
 if aW <> nil then
   windowpeek(aW)^.windowKind := DCE^.dCtlRefNum;
   NumToString(NumWindows, WindowNo);
   SetWTitle(aW, concat(OurName, ‘ ‘, WindowNo));
   WindowCounter := NumWindows;
   NumWindows := NumWindows + 1;
 OpenAWindow := aW

{PROCEDURE CloseAWindow closes down one of our windows and decrements 
the NumWindows counter, in a more sophisticated desk accessory, it would 
handle disposing of the various data structures, files, etc. associated 
with the window. Note that if the window we’re closing is the same as 
that stored in the dCtlWindow field, we must update the field to point 
to a current valid window. Local procedure UpdateDCE handles this task.}
procedure CloseAWindow (aWindow: WindowPtr);

{Procedure UpdateDCE sets the DCE^.dCtlWindow field to point to our topmost 
open window.  The dCtlWindow field should always point to a valid window 
or the desk accessory will die horribly in a matter of ticks.}
procedure UpdateDCE;
  aWindow: WindowPeek;
  DCE^.dCtlWindow := nil ;
  aWindow := WindowPeek(FrontWindow);
  while aWindow <> nil do
   if aWindow^.WindowKind = DCE^.dCtlRefNum then
     DCE^.dCtlWindow := pointer(aWindow);
    aWindow := aWindow^.NextWindow;
 end; {PROCEDURE UpdateDCE}

begin {PROCEDURE CloseAWindow}
 NumWindows := NumWindows - 1;

 if DCE^.dCtlWindow = aWindow then

{ ********************************************** }
{ ***************** Menu Handlers*************** }
{ ********************************************** }

{PROCEDURE DoApple handles the apple menu}
procedure DoApple (itemNo: integer);
 dummy: integer;
 name: str255;
 if itemNo = AboutItem then
  dummy := Alert(GetResId(AboutID), nil )
   GetItem(OurMenus[applemenu], itemNo, name);
   dummy := OpenDeskAcc(name);

{PROCEDURE DoFile handles the file menu}
procedure DoFile (ItemNo: integer);
 dummy: windowptr;
 case ItemNo of
   dummy := OpenAWindow;
   done := true;

{PROCEDURE DoEdit handles the Edit Menu}
procedure DoEdit (ItemNo: integer);
 OurDlog: DialogPtr;
 dummy: integer;
 OurDlog := FrontWindow;
 if OurDlog <> nil then
   {Move the public scrap to the TE scrap for the dialog manager’s use.}
   dummy := TEFromScrap;
   case ItemNo of
   {Move the TE scrap to the public scrap.}
   dummy := ZeroScrap;
   dummy := TEToScrap

{PROCEDURE DoWindowMenu handles the Windows menu}
procedure DoWindowMenu (itemNo: integer);
 case itemNo of
   modifyWindows(FrontWindow, CleanupProc);

{PROCEDURE DoMenus is the main dispatch for all menu selections. Since 
the menu IDs are determined onlyat run time, we cannot use a CASE constant 
structure here. Instead, we use a series of IF ELSE statements to determine 
which of our menus was chosen.}
procedure DoMenus (MenuNo, ItemNo: integer);
 Str1, Str2: str255;
 dummy: integer;
 OurDlog: dialogptr;
 if MenuNo = MenuIDs[AppleMenu] then
 else if MenuNo = MenuIDs[FileMenu] then
 else if MenuNo = MenuIDs[EditMenu] then
 else if MenuNo = MenuIDs[WindowMenu] then

{*********** Event Handling Routines ***********}

{PROCEDURE DoActivate handles activate/deactivate events in our DA’s 
windows. On an activate event we install the DA’s menu bar and update 
DCE^.dCtlWindow field to point to the active window. This assures that 
if our DA is later selected from the application’s apple menu, our current 
active window will be brought to the foreground.}
procedure DoActivate (var Evt: eventrecord);
 active: boolean;
 theWindow: Windowptr;
 kind: integer;
 active := BitAnd(Evt.modifiers, activeFlag) <> 0;
 if active then
   theWindow := pointer(Evt.message);
   kind := windowPeek(theWindow)^.windowkind;
   if kind <> DCE^.dctlRefNum then
   DCE^.dCtlWindow := theWindow;

{FUNCTION MetaKey checks whether the cloverleaf key was pressed during 
keypress. If so, it gets the menu and item from DAMenuKey and passes 
the menu selection on to DoMenus. If the cloverleaf was not depressed, 
then MetaKey returns FALSE so that the caller knows to handle the keypress 
function MetaKey(var Evt: eventrecord): boolean;
 aChr: char;
 Tangled: longint;
 if BitAnd(cmdKey, Evt.modifiers) <> 0 then
   aChr:= Char(BitAnd(Evt.message, charCodeMask));
   Tangled:= DAMenuKey(aChr);
   DoMenus(HiWord(Tangled), LoWord(Tangled));
   MetaKey:= true
  MetaKey:= false;

{PROCEDURE DoIdle gets called for null events. It does two things:
{ 1. It checks the cursor and changes it into an I-beam when the cursor 
is over the window’s text edit field. }
{ 2. It manufacturer’s a “dummy” null event and calls DialogSelect so 
that the text edit cursor gets flashed.}
{This is the place to do any other background processing.}
procedure DoIdle;
 theDlog: DialogPtr;
 itemHit: integer;
 event: EventRecord;
 dummy: boolean;
 aPt: point;
 theDlog := DCE^.dctlWindow;

{First make the mouse into an I-Beam if we’re above the text field}
 with dialogPeek(theDlog)^ do
    if textH <> nil then
     if PtInRect(aPt, textH^^.viewRect) then

{Next call DialogSelect with a null event in order to blink the cursor}
 event.what := NullEvent;
 dummy := dialogSelect(event, theDlog, Itemhit)

{PROCEDURE HandleEvents is the main dispatcher for all events appertaining 
to our DA.}
procedure HandleEvents (var Evt: EventRecord);
 dummy: windowptr;
 itemHit: integer;
 WhichDialog: DialogPtr;

{We do some pre-processing before calling DialogSelect}
 case Evt.what of
  KeyDown, AutoKey:
   if MetaKey(Evt) then

{Here we call DialogSelect to do most of the housekeeping window tasks}
 if DialogSelect(Evt, whichDialog, Itemhit) then
  case itemHit of
    dummy := OpenAWindow;
     SelIText(whichDialog, EditText, 0, 10000);
end; {procedure HandleEvents}

{**************** Main DA Routines **************}

{ ================== CLOSE ======================}
function CLOSE: OSErr;
 i: integer;
 Close := NoErr;

{If we don’t have any window, then we haven’t been opened and Close is 
being called}
 if DCE^.dCtlWindow = nil then

{Clean up after ourselves}
 with DCE^ do
   ModifyWindows(FrontWindow, CloseAWindow);
   dctlWindow := nil ;

   for i := 0 to WindowMenu do
   dCtlMenu := 0;

end; {of function CLOSE}

{ ================ OPEN =====================}
function OPEN (DCTlE: DCtlPtr;
       IOPB: ParmBlkPtr): OsErr;
 aWind: WindowPeek;
 open := NoErr;
 OurName := IOPB^.ioNamePtr^;
 with DCE^ do

   if dctlWindow = nil then

{The window is nil, so initialize and allocate everything!}
     if dCtlStorage = nil then
       Open := OpenErr;
       dctlWindow := OpenAWindow;
       dCtlMenu := InitMenus;

{If we get here, then we are already open.  We must bring all our windows 
forward. First bring forward all windows below our topmost DA window. 
This has the effect of bringing forward ALL our windows when the DA is 
selected without changing their relative order. Next select our topmost 
window to bring it to the front.  The topmost window is already stored 
in the DCE^.dctlWindow field.}

     aWind:= WindowPeek(dctlWindow)^.nextWindow;
     ModifyWindows(aWind, BringWindowForward);

 {Now select our topmost window}
  end; {of WITH clause}
end; {of OPEN}

{=================== CONTROL =================== }
function CONTROL (IOPB: ParmBlkPtr): OsErr;
 accGoodBye = -1;
 EventPtr = ^EventRecord;
 APort: GrafPtr;

begin {functon CONTROL}

 Control := NoErr;

{Dispatch for all the different control calls}
 case IOPB^.csCode of
   DoMenus(IOPB^.csParam[0], IOPB^.csParam[1]);
   Control := Close;
 end; {of case statement}

end; {function CONTROL}

{************MAIN FUNCTION*****************}
{FUNCTION Main is the entry point for the DA. THINK Pascal will intercept 
the driver (OPEN/CLOSE/CONTROL) call and funnel it through this routine, 
along with a pointer to the device control entry, the parameter block, 
and a selector indicating which driver call was made. Pascal very nicely 
sets up a global storage block}
function MAIN (DCtlE: DCtlPtr;
       IOPB: ParmBlkPtr;
       driveCall: Integer): OSErr;
{Need to call RememberA4 up front if our dialogs have user items or if 
we get called at interrupt time.  This code doesn’t use these features, 
but call it just in case.}
 Done := false;
 DCE := DCtlE;

 case driveCall of
   Main := Open(DCtlE, IOPB);
   with DCE^ do
{Turn off further control calls while servicing this one in order to 
avoid re-entrancy issues}
     dCtlFlags := BitAnd(dCtlFlags, $FBFF);
     Main := Control(IOPB);
     dCtlFlags := BitOr(dCtlFlags, $0400);
   if NumWindows > 1 then
{We have more than one window open, so just close topmost}
     Main := CloseErr
    Main := Close;
  DriverStatus, DriverPrime:
   Main := NoErr;
 end; {case statement}

{This happens when the user selects “quit” from the menus or there is 
a fatal error.}
 if Done then
   Main := Close;
end; {of MAIN function}
end. {of the whole unit}

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