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CMD-Shift-3
Volume Number:2
Issue Number:8
Column Tag:Assembly Language Lab

CMD-Shift-3 Patch for the New ROMS

By Harvey Grosser, Oakland, CA

Menu Snapshots with the new ROMs

As was described in the July MacTutor, attempting to take a screen dump with a menu pullled down on a machine with the 128K ROM results in the menu snapping up before the dump is taken. Also, on both old and new ROMs, pulling down a menu results in the Alarm clock (and any other desk accessories which require periodic updates) freezing, because no call is made to SystemTask by the Menu Manager. This short patch fixes both of these problems.

First, we need to patch the menu definition 0 resource in the system file. To do that, start up ResEdit and open the system file. Select MDEF 0 resource. Double-click on it and insert the following code at the beginning of the resource:

9EFC 0012 3F3C 0008
486F 0004 A970 DEFC
0012 A9B4

You may want to set the system heap flag as well to improve performance. This will cause it to be loaded once by the Finder and then remain on the system heap for subsequent applications.

Fig. 1 It Works Again on a Mac Plus!

Now close and save the system file. Assemble and link the INIT resource at the end of this article, and paste it into your system file. (Note: Make sure that the ID of this INIT, (17), does not duplicate that of an existing one-change if if necessary.) When you run an application, you will find that pressing Command-Shift-3 with a menu pulled down results in a screen dump being taken immediately, without waiting for the mouse to be released. This permits multiple snapshots to be taken from the same menu without having to pull it down each time, a boon when documenting a long menu. Also, desk accessories will no longer freeze when a menu is down, although they will still freeze when the cursor is in an unused part of the menu bar.

How it Works

This is the source code for this patch above:

SUBA.W  #18,SP ;stack space for evt record, result
MOVE.W  #8,-(SP) ;keydown event mask
PEA4(SP);address of evt record VAR param
_GetNextEvent
ADDA.W  #18,SP ;discard function result & event rec
_SystemTask ;allow DAs to work

Since the menu definition function is executed repeatedly while a menu is pulled down, this results in calls to GetNextEvent with an event mask which permits it to take key down events from the system event queue. When it sees one of these, it executes the appropriate FKEY routine if a Command-Shift-number key combination was pressed. The call to SystemTask permits desk accessories to run. The INIT routine is necessary because the new resource manager uses the MDEF 0 in ROM rather than the one in the System File. (See the Aug. '85 issue of MacTutor for info on the INIT resources.) The patch functions by setting ROMmapInsert to 0 before every call to GetResource when the type asked for is MDEF or FONT. (This permits editing the Chicago font, some characters of which I consider really bad.) It is necessary to patch GetResource directly like this because the Menu Manager always sets ROMmapInsert to TRUE before making the call. I would really appreciate it if someone out there could give the exact meaning of the individual bytes at $B9E (ROMmapInsert) and $B9F (TempResLoad); Apple's Tech Note #57 is rather vague on this.

; MDEFINIT.ASM
; place this INIT in system file
; to fix cmd-shift-3 bug

;Place this patch in MDEF 0
;resource (at beginning), in
;your system file:
;
;9EFC 0012 3F3C 0008
;486F 0004 A970 DEFC
;0012 A9B4
;
;Patch meaning:
;
;SUBA.W #18,SP
;MOVE.W #8, -(SP)
;PEA  4(SP)
;_GETNEXTEVENT
;ADDA.W #18,SP
;_SYSTEMTASK
;

INCLUDE MACTRAPS.D

GetResource equ  $A9A0  ;trap address
ROM85   equ $28E ;new ROM= $7FFF 
RomMapInsert   equ   $B9E 

RESOURCE'INIT' 17'MDEF Init' $50 ;SysHeap+locked

start:  
 BRA.W  after
patch:  
 CMPI.L #'MDEF', 6(SP)  ;check type
 BEQ.S  @1;for MDEF or FONT;
 CMPI.L #'FONT', 6(SP)  ;if not,
 BNE.S  jump;don't change map
@1:
 CLR.W  ROMmapInsert
jump: 
 JMP  $12345678  ;filled in by init routine

after:  
 LEA  start,A0 
 _RecoverHandle  ;handle to proc
 TST.W  ROM85  ;new roms? (7FFF)
 BPL.S  newROM ;yes, go for it
 _DisposHandle   ;no, forget it
 RTS    ;and exit
 
newROM: 
 MOVE.L #after-start,D0 ;get our size
 _SetHandleSize  ;chop off init routine
 MOVE.W #GetResource,D0 
 _GetTrapAddress ;addr of GetResource
 LEA  jump+2,A1  ;paste it into patch
 MOVE.L A0, (A1) ;patch it
 LEA  patch, A0  
 MOVE.W #GetResource,D0 
 _SetTrapAddress ;install patch
 RTS
 END
 

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