//

    //  This is "jGNE Helper", formerly a monthly posting to

    //  the Usenet newsgroup alt.sources.mac.

    //  It provides an example for INIT programmers

    //  interested in filtering events before they are handed to

    //  applications calling GetNextEvent (which is called by

    //  WaitNextEvent).

    //  

    //  The jGNE filter is the Apple-sanctioned method for

    //  filtering events. It is possible to patch event traps. It

    //  is sometimes even advisable. But since the jGNE filter is

    //  the sanctioned method, one ought to attempt to use it

    //  before patching traps.

    //

    //  Prospective users of this code should know that the

    //  plan of record for Copland does not include support

    //  for jGNEFilter. However, it is likely that Copland

    //  will include some form of global event filtering service.

    //  Carefully isolate your use of this code and you may

    //  be able to make the move to Copland without too much

    //  pain.

    //

    //  This code sample has a specific conflict with older

    //  versions of PopChar. Newer versions of PopChar have a fix

    //  which makes them compatible with this code. Users of older

    //  versions of PopChar should probably upgrade to the current

    //  version anyway -- this is a very old conflict. The conflict

    //  manifests itself by rendering a good portion of the screen

    //  "impervious" to clicks unless the option key is held down.

    //  

    //  This version of jGNE Helper was built with both Symantec

    //  THINK C 7 and Metrowerks CodeWarrior CW7 for 68K machines.

    //  It's entirely possible to write a native jGNEFilter. I've

    //  even done it before. However, it hasn't occurred to me how

    //  to fit a native filter into the context of this sample.

    //  

    //  For further info on the jGNE filter, consult your Technotes.

    //

#ifndef THINK_C

#   ifndef __MWERKS__

#       error unknown compiler

#   endif

#endif

#define OLDROUTINENAMES         0

#define OLDROUTINELOCATIONS     0

#ifndef __RESOURCES__

#   include <Resources.h>

#endif

#ifndef __MEMORY__

#   include <Memory.h>

#endif

#ifndef __EVENTS__

#   include <Events.h>

#endif

#ifndef __SETUPA4__

#   include <SetUpA4.h>

#endif

#ifndef __LOWMEM__

#   include <LowMem.h>

#endif

    //

    //  This example filter simply watches for clicks

    //  with the command, option, and control keys held

    //  down. If it finds any, it beeps and returns a

    //  value which indicates the event should not be

    //  passed to the application which called GNE.

    //

static Boolean myGNE (EventRecord *event, Boolean preResult)

{

    Boolean postResult = preResult;

    if (preResult)

    {

        if (event->what == mouseDown)

        {

            if (event->modifiers & cmdKey)

            {

                if (event->modifiers & optionKey)

                {

                    if (event->modifiers & controlKey)

                    {

                        SysBeep (10);

                        postResult = false;

                    }

                }

            }

        }

    }

    return postResult;

}

static void     *gOldJGNE;

static Boolean  inJGNE;

#if defined (THINK_C)

static pascal void myJGNE (void)

{

    asm

    {

            MOVE.L      A1,A0           // save event record pointer from __GetA4

            JSR         __GetA4         // point A1 at our A4

            MOVE.L      A4,-(A7)        // save old A4

            MOVE.L      (A1),A4         // get new A4

            MOVE.L      A0,A1           // restore old A1

#elif defined (__MWERKS__)

static pascal asm void myJGNE (void)

{

            MOVE.L      D0,A0           // save pre-result from SetUpA4

            JSR         SetUpA4         // fix A4, stomp D0

            MOVE.L      D0,-(A7)        // save old A4

            MOVE.L      A0,D0           // restore pre-result

#endif

            TST.B       inJGNE          // is myJGNE busy?

            BNE         @1              // yes, so bail

            MOVE.B      #true,inJGNE    // mark myJGNE busy

            MOVE.W      D0,-(A7)        // push pre-result

            MOVE.L      A1,-(A7)        // push event record pointer

            JSR         myGNE           // do the real work

            MOVE.L      (A7)+,A1        // restore event record pointer

            ADDQ.L      #2,A7           // pop pre-result; post-result in D0

            ASL.W       #8,D0           // bump C boolean to Lisa

            MOVE.W      D0,8(A7)        // stash result where caller expects it

            MOVE.B      #false,inJGNE   // mark myJGNE not busy

@1:

            MOVE.L      gOldJGNE,A0     // get previous jGNE

            MOVE.L      (A7)+,A4        // restore A4

            MOVE.L      A0,-(A7)        // return to previous jGNE

#if defined (THINK_C)

        }

#elif defined (__MWERKS__)

            RTS

#endif

}

#if defined (__MWERKS__)

#   include <A4Stuff.h>

#elif defined (THINK_C)

    pascal void * GetA0 (void) = { 0x2E88 };

#endif

void main (void)

{

#if defined (__MWERKS__)

    void __Startup__ (void);

    long oldA4 = SetCurrentA4 ( );

    RememberA4 ( );

    DetachResource (RecoverHandle ((Ptr) __Startup__));

#elif defined (THINK_C)

    void *me = GetA0 ( );

    RememberA0 ( );

    DetachResource (RecoverHandle (me));

    SetUpA4 ( );

#endif

    gOldJGNE = LMGetGNEFilter ( );

#if defined (__MWERKS__)

    LMSetGNEFilter (myJGNE);

#elif defined (THINK_C)

    LMSetGNEFilter ((ProcPtr) myJGNE);

#endif

#if defined (__MWERKS__)

    SetA4 (oldA4);

#elif defined (THINK_C)

    RestoreA4 ( );

#endif

}