TweetFollow Us on Twitter

Jan 90 Letters
Volume Number:6
Issue Number:1
Column Tag:Letters

INITs First

By David E. Smith, Editor & Publisher, MacTutor

INITs in Pascal or C

Steve Brecher

Sunnyvale, CA

There are some problems in the advice and code provided in the October 1989 issue’s Pascal Procedures and C Workshop, which discuss writing INITs in the respective languages.

The VBL task shown in Pascal Procedures calls GetGDevice without checking whether Color QuickDraw is available. It assumes that the current GDevice is the monitor the mouse is on. Multiple-monitor users may be surprised to find the mouse jumping from the middle of one monitor to the opposite edge of another when they press Option for some application purpose. The code also assumes, in its reference to QuickDraw globals through CurrentA5, that QuickDraw has been initialized for the currently executing application. This is not necessarily true.

The following comments apply to the C Workshop article.

The author does not understand the function of the ioNamePtr field in File Manager parameter blocks. This field contains either a pointer to a caller- allocated string buffer or nil if the caller chooses not to pass or receive a filename string. The File Manager does not allocate a string buffer for the caller.

INIT 31 does not necessarily expand the system heap by the amount specified in your ‘sysz’ 0 resource, and it certainly does not “collapse” the heap to undo any previous expansions--CompactMem collects free blocks together; it does not shrink a heap. What INIT 31 does is expand the system heap if necessary to assure that a contiguous block of the size specified in the ‘sysz’ 0 resource is available at the time the first (and usually only) INIT resource in an INIT/

cdev/RDEV is executed. Any space gained by heap expansion that is not used by the INIT will remain free when the INIT exits--but may be sopped up by subsequent INITs or system activity.

The author unduly discounts the dangers of tail patching. A tail patch is a trap patch that calls (JSRs to) the original patch instead of JMPing to it. A tail patch may nullify an Apple-supplied ROM code patch. Such Apple patches operate by comparing their return address on the stack with certain hard-coded ROM addresses. By JSRing to the original trap code, one assures that such a comparison will always fail since the Apple patch will see one’s own return address rather than that of the original trap caller. In some cases tail patching is necessary; my own products do it. But one should at least check the latest System release to make sure that one’s tail patches do not nullify ROM code patches. And in some cases one can eat one’s cake and have it too by JSRing to the original trap code, doing necessary post-processing, and then JMPing to the original code. The original code will be executed twice, and the second execution will invoke any ROM patch code that may be installed. The JMP requires assembly language.

The example INIT ignores the fact that Resource Manager traps preserve all registers except D0/A0 (except LoadResource, which preserves all including D0/A0)--IM I-113. It also uses the Dialog Manager with no assurance that it has been intialized, not to mention QuickDraw, etc.

Writing Inits in Pascal

Roland van Straten

Dutch Macintosh Developer

Perhaps this is not the right way to inform you about bugs, but sending a letter takes a while and it has no way to send real program listings. So if this is not the way you prefer, let me know.

I’ve read the article about “Writing INITs in Pascal”, MacTutor Oct 89, Page 51, and after some study of the source code I noticed two bugs. Maybe Steve Kiene’s system and/or compiler do something special or he forgot to test it, I don’t know.

1. The MTemp location has a counterpart: RawMouse. It’s the next LongInt in Low Memory. If RawMouse is equal to MTemp the mouse handler will think the move has to be made absolute. Otherwise the move will be treated as relative (Steve Kiene’s program).

2. The CrsrNew location is a Byte value. Steve Kiene’s program declares a pointer to a Byte (^Byte). This is a two byte value. Look at IM vol1, pag 86. In order to fix this I used a standard type Ptr (^SignedByte) and exchanged $FF for -1.

Apart from these little bugs I enjoyed the article very much and found it useful. The article appeared at the time I was writing a VBL task that moves the mouse “outside” the screen (don’t ask me for the reason of this).

UNIT CursorWrap;

{MacTutor ©1989, issue October 1989, page 51, “Writing INITs in Pascal” 
by Steve Kiene}

{MPW 3.0 version - October 1989 - ROLAnd van Straten - ALink HOL0027}





 theVBL : VBLTask;
 myQElem: QElemPtr;
 myErr  : OSErr;
 SaveZone : THz;
 PatchPtr : Ptr;
 theCode: Handle;
 thePtr : ^LongInt;

 theCode:= Get1Resource(‘INIT’,1);
 SaveZone := GetZone;
 SizeNeeded := SizeResource(theCode) - (LongInt(@SetUpVBL) - LongInt(theCode^)) 
+ SizeOf(QElem);
 IF MemError <> NoErr THEN BEGIN
 SysBeep(1); SetZone(SaveZone); Exit(SetUpVBL); END;
 PatchPtr := NewPtr(SizeNeeded + 4) ;{get ptr for our code}
 BlockMove(@Wrap, Pointer(ORD(PatchPtr)+4), SizeNeeded);
 myQElem := QElemPtr(NewPtr(SizeOf(QElem)));
 {put vbl task ptr addr into ptr where our patch will be}
 thePtr := Pointer(PatchPtr);
 thePtr^ := LongInt(myQElem);
 qType  := ORD(vType);
 vblAddr  := Pointer(ORD(PatchPtr)+4);
 vblCount := 6;
 vblPhase := 0;
 myQElem^.vblQElem := theVBL;
 myErr := VInstall(myQElem);

{Wrap cursor when option key is down

 MTemp  has latest mouse value
 RawMouse has the un-jerked mouse value
 CrsrNew  must be set to “-1” to indentify “moved”
 If MTemp and RawMouse are different there only will be a relative change 
of the mouse position. This looks like unstable moves on the screen. 
 Fixed this bug by moving RawMouse into the arena.
 CrsrNew is a byte. The used pointer type was a ^Byte. This is in fact 
a two byte value (WRONG). Look in IM.1 pag 68 for details on this. So 
in order to fix this use the standard Ptr type and put the value -1 into 
the addressed byte.

 CurrentA5 = $904;
 MTemp  = $828;  {Low-level interrupt mouse location [long]}
 RawMouse = $82C; {un-jerked mouse coordinates [long]}
 CrsrNew= $8CE; {Cursor changed? [byte]}
 OptionKey= 58;

 LPtr = ^LongInt;

 myQElem: QElemPtr;
 currGDevice: GDHandle;
 theMap : KeyMap;
 changed: Boolean;
 myRectPtr: ^Rect;
 mouseRect, myRect : Rect;
 myPtr,myPtr2    : LPtr;
 PPtr,P2Ptr : ^Point;

 IF theMap[OptionKey] THEN BEGIN
 changed := FALSE;
 currGDevice :=GetGDevice;
 IF currGDevice <> NIL THEN
 mouseRect := currGDevice^^.gdRect
 BEGIN {use A5 to get offset to screenbits.bounds}
 myPtr  := Pointer(CurrentA5);
 myPtr2 := Pointer(myPtr^);
 myRectPtr := Pointer(myPtr2^-116);
 mouseRect := myRectPtr^;
 PPtr := Pointer(MTemp); P2Ptr := Pointer(RawMouse);
 IF PPtr^.v <= THEN BEGIN {check cursor pos for wrap}
 PPtr^.v  := mouseRect.bottom -1;
 P2Ptr^.v := mouseRect.bottom -1;
 changed  := TRUE; END
 IF PPtr^.v >= mouseRect.bottom THEN BEGIN
 PPtr^.v  := +1;
 P2Ptr^.v := +1;
 changed  := TRUE; END
 IF PPtr^.h <= mouseRect.left THEN BEGIN
 PPtr^.h  := mouseRect.right -1;
 P2Ptr^.h := mouseRect.right -1;
 changed  := TRUE; END
 IF PPtr^.h >= mouseRect.right THEN BEGIN
 PPtr^.h  := mouseRect.left +1;
 P2Ptr^.h := mouseRect.left +1;
 changed:= TRUE; END;
 IF changed THEN 
 Ptr(CrsrNew)^ := -1;{cursor has changed}
 myQElem := QElemPtr(LPtr(Pointer(ORD(@Wrap)-4))^);      {get ptr to 
vbl task, and reset it}
 myQElem^.vblQElem.vblCount := 6;


INIT Inhibition

David Dunham

Seattle, WA

Just a quick note about Peter Hoddie’s article on INITs. He suggests that INITs not install themselves when the mouse button is down.

In fact, there is a fairly standard method of inhibiting INITs: the shift key. Not all INITs use this, but probably half the ones I’m familiar with do. My own INITs also disable themselves when their initial letter (e.g. ‘f’ for Findswell) is held at boot time.

The problem with using the mouse button is that it instructs the Mac to eject the internal disk at boot time. Disabling INITs shouldn’t be a matter of timing just when to click the mouse.


Community Search:
MacTech Search:

Software Updates via MacUpdate

Warhammer 40,000: Freeblade guide - How...
Warhammer 40,000: Freebladejust launched in the App Store and it lets you live your childhood dream of blowing up and slashing a bunch of enemies as a massive, hulking Space Marine. It's not easy being a Space Marine though - and particularly if... | Read more »
Gopogo guide - How to bounce like the be...
Nitrome just launched a new game and, as to be expected, it's a lot of addictive fun. It's called Gopogo, and it challenges you to hoparound a bunch of platforms, avoiding enemies and picking up shiny stuff. It's not easy though - just like the... | Read more »
Sago Mini Superhero (Education)
Sago Mini Superhero 1.0 Device: iOS Universal Category: Education Price: $2.99, Version: 1.0 (iTunes) Description: KAPOW! Jack the rabbit bursts into the sky as the Sago Mini Superhero! Fly with Jack as he lifts impossible weights,... | Read more »
Star Wars: Galaxy of Heroes guide - How...
Star Wars: Galaxy of Heroes is all about collecting heroes, powering them up, and using them together to defeat your foes. It's pretty straightforward stuff for the most part, but increasing your characters' stats can be a bit confusing because it... | Read more »
The best cooking apps (just in time for...
It’s that time of year again, where you’ll be gathering around the dinner table with your family and a huge feast in front of you. [Read more] | Read more »
Square Rave guide - How to grab those te...
Square Rave is an awesome little music-oriented puzzle game that smacks of games like Lumines, but with its own unique sense of gameplay. To help wrap your head around the game, keep the following tips and tricks in mind. [Read more] | Read more »
Snowboard Party 2 (Games)
Snowboard Party 2 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Crowned the best snowboarding game available on the market, Snowboard Party is back to fulfill all your adrenaline needs in... | Read more »
One Button Travel (Games)
One Button Travel 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: “To cut a long story short, If you like interactive fiction, just go buy this one.” - “Oozes the polish that... | Read more »
Light Apprentice Volume 1 (Games)
Light Apprentice Volume 1 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Light Apprentice Volume 1 includes Chapters 1 to 4, all gathered in a new exclusive game. When life in the world of... | Read more »
The best games like Animal Crossing on m...
Animal Crossing amiibo Festival is out right now for the Wii U, reminding us of just how much fun that world can be. Or at least to go back and check in on our villages once in a while. [Read more] | Read more »

Price Scanner via

iMobie Releases its Ace iOS Cleaner PhoneClea...
iMobie Inc. has announced the new update of PhoneClean 4, its iOS cleaner designed to reclaim wasted space on iPhone/iPad for use and keep the device fast. Alongside, iMobie hosts a 3-day giveaway of... Read more
U.S. Cellular Offering iPad Pro
U.S. Cellular today announced that it is offering the new iPad Pro with Wi-Fi + Cellular, featuring a 12.9-inch Retina display with 5.6 million pixels — the most ever in an iOS device. U.S. Cellular... Read more
Newegg Canada Unveils Black Friday Deals for...
Newegg Canada is offering more than 1,000 deep discounts to Canadian customers this Black Friday, available now through Cyber Monday, with new deals posted throughout the week. “Black Friday is... Read more
Black Friday: Macs on sale for up to $500 off...
BLACK FRIDAY B&H Photo has all new Macs on sale for up to $500 off MSRP as part of their early Black Friday sale including free shipping plus NY sales tax only: - 15″ 2.2GHz Retina MacBook Pro: $... Read more
Black Friday: Up to $125 off iPad Air 2s at B...
BLACK FRIDAY Walmart has the 16GB iPad Air 2 WiFi on sale for $100 off MSRP on their online store. Choose free shipping or free local store pickup (if available): - 16GB iPad Air 2 WiFi: $399, save $... Read more
Black Friday: iPad mini 4s on sale for $100 o...
BLACK FRIDAY Best Buy has iPad mini 4s on sale for $100 off MSRP on their online store for Black Friday. Choose free shipping or free local store pickup (if available): - 16GB iPad mini 4 WiFi: $299.... Read more
Black Friday: Apple Watch for up to $100 off...
BLACK FRIDAY Apple resellers are offering discounts and bundles with the purchase of an Apple Watch this Black Friday. Below is a roundup of the deals being offered by authorized Watch resellers:... Read more
Black Friday: Target offers 6th Generation iP...
BLACK FRIDAY Save $40 to $60 on a 6th generation iPod touch at Target with free shipping or free local store pickup (if available). Sale prices for online orders only, in-store prices may vary: -... Read more
Black Friday: Walmart and Target offer iPod n...
BLACK FRIDAY Walmart has the 16GB iPod nano (various colors) on sale for $119.20 on their online store for a limited time. That’s $30 off MSRP. Choose free shipping or free local store pickup (if... Read more
Black Friday deals on the Apple Watch and App...
Apple resellers are offering discounts and bundles with the purchase of an Apple Watch this Black Friday weekend. Below is a roundup of the deals being offered by authorized Watch resellers: Apple... Read more

Jobs Board

Storefront Operations Coordinator, *Apple* -...
# Storefront Operations Coordinator, Apple -Latin America Job Number: 43587750 Miami, Florida, United States Posted: Oct. 16, 2015 Weekly Hours: 40.00 **Job Summary** The Read more
*Apple* Enterprise / Government Professional...
# Apple Enterprise / Gove ment Professional Services Engineer Job Number: 42292976 Reston, Virginia, United States Posted: Aug. 18, 2015 Weekly Hours: 40.00 **Job Read more
iOS Wallet & *Apple* Pay Engineer - App...
# iOS Wallet & Apple Pay Engineer Job Number: 40586801 Santa Clara Valley, Califo ia, United States Posted: Nov. 16, 2015 Weekly Hours: 40.00 **Job Summary** The iOS Read more
Software Engineer, *Apple* Watch - Clock Fa...
# Software Engineer, Apple Watch - Clock Face Team Job Number: 44368761 Santa Clara Valley, Califo ia, United States Posted: Nov. 14, 2015 Weekly Hours: 40.00 **Job Read more
Administrative Assistant, *Apple* Online St...
# Administrative Assistant, Apple Online Store Job Number: 43992352 Santa Clara Valley, Califo ia, United States Posted: Nov. 9, 2015 Weekly Hours: 40.00 **Job Summary** Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.