TweetFollow Us on Twitter

Mar 94 Tips
Volume Number:10
Issue Number:3
Column Tag:Tips & Tidbits

Tips & Tidbits

Using GWorlds and the Pallette Manager

Edited by Scott Boyd and Neil Ticktin

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

Tip Of The Month

Studies have shown that anyone who has to focus visual attention in one place for a long time (like a computer user), will blink less often. This makes your eyes dry, and is the main cause of eyestrain. Even though blinking is a reflex action and usually outside of conscious control, there’s an easy way to increase your blink-rate.

Write the word “Blink!” on a small piece of paper. Then stick it someplace on your computer monitor where you will always be able to see it. Put one on every monitor you have. Every time you notice it, follow the instruction: Blink a couple of times, and look away from your monitor to focus on some distant object for a few seconds. Then get back to work before your boss catches you staring off into space.

You’ll notice the paper a lot at first, eventually less often. The initial effect is just to make you think about it. But even after you stop noticing it consciously, leave the note there. It has a subliminal “training” effect that makes you blink more often. It’s like tying a string around your finger to help you remember something. This really works to reduce eyestrain. But it’s so simple and inexpensive that most people don’t believe it until they’ve used it for a while.

- Lee David Rimar, Absoft Corporation

[As with all tips, consult your physician before trying this at home! - Ed. nst]

This column is your opportunity to spread the word about little bits of information that you find out about. These tidbits can be programming related or they can be user tips that are particularly useful to programmers.

MacTech Magazine will pay $25 for every tip used, and $50 for the Tip of the Month. Or you can take your award in orders or subscriptions.

To submit a tip, send in a letter to the magazine. E-mail is our preferred method, but feel free to send something via the US Mail. See page two for all addresses. If you do send snail mail, enclose a printed copy and a disk copy of the letter so that it does not have to be retyped.

Down and dirty

The following two MOVE instructions will load a zero into lower D0 on a 68000 processor and a one on 68020 or better.


/* 1 */
; Get offset to be scaled
303C 0001  Move.W  #1,D0

; Get one of the two bytes 00 or 01!
103B 02FB  Move.B  *-3(PC,D0.W*2),D0 

This is a much cheaper way than _Gestalt to find out if the 32x32 => 64 multiply instructions are available, etc. To see why this works, first consider 68020 or better hardware. After the Move.W instruction lower D0 will contain the value one. The *-3(PC) part of the Move.B addresses the 3C byte of the Move.W instruction, but indexing by D0 is also specified. Since the scaling field is two, the effective index is two times one or two. Thus the Move.B fetches the byte two down from the 3C byte, which is the 01 byte. Thus on 68020 or better hardware we get a one.

Now consider 68000 hardware. It does not implement index scaling, nor does it notice it being called for! Thus a 68000 will execute the Move.B instruction as if it were the instruction:


/* 2 */
 Move.B  *-3(PC,D0.W),D0

Now the effective index is one (not two) and the zero byte that is one down from the 3C byte is loaded. Thus on 68000 hardware we get a zero. Note also that the Zero toggle will be set on 68000 and cleared on 68020 or better hardware. This allows an immediate BZ/BEq or BNZ/BNE to be used.

The information that the 68000 processor fully decodes all 16384 possible opcode words but does not fully decode the addressing modes in extension words can be found in the Advanced Topics appendix of Motorola's MC68020 32-Bit Microprocessor User's Manual (Second Edition).

- Charles Cranston

zben@ni.umd.edu

Starting an init

I always the following code for the entry point for an INIT, WDEF or any other code resource. This template can only be used with Think C, as it uses assembly and it relies on A4 to reference globals. The 'Custom Header' must be checked in the 'Set Project Type '-dialog.


/* 3 */
void main (void) ;
void header (void) ;

void header (void)
{
  asm {
    BRA.S  @next   ; jump over the following data
    DC.L   'TMON'  ;   tell TMON todo label-searching
    DC.L   'INIT'  ;   use this and the next 4 bytes to label
    DC.L   'SPPS'  ;   this code resouce
 next:
    LEAheader, A0  ; load the address of the code resource in A0
    JMP    main  ; jump to main
  }
}

#include <SetUpA4.h>   // We need this if we have globals

void main (void)
{ Ptr  mySelf ;  // pointer to this code resource

  asm {
    move.l A0, mySelf
  }

  RememberA0()   ;  // put A0 in a save spot
  SetUpA4() ;  // and use it to set up A4
        
  RestoreA4() ;

The low-level debugger TMON looks for MacsBug labels in code resources that it knows about. If it doesn’t know the type of a resource to be code, or if it is detached and no longer a resource, TMON will not show labels in the code. The TMON User Area 'AddRange/TMON.fixed' looks for the string 'TMON' two bytes into every block it finds, and then asks TMON to scan it for labels. It was written by Ken Schalk and it is available on bulletin boards.

The following two strings mark what the block is about. This is great for debugging. If I want to set a breakpoint, I simply search for these strings in memory,

After the 'next' label, I load the address of the start of the code resource in register A0. This is required by Think C so that it can retrieve it to set A4 for accessing globals. The statements RememberA0() and SetUpA4() do the trick. Always be sure to call RestoreA4() before leaving the routine. A0 contains a pointer to the start of the block, and I save it in the variable 'mySelf'. If I want to keep the code in memory afterwards, I simply have to execute 'DetachResource(RecoverHandle(mySelf))'.

- Jan Bruyndonckx

Wave Research, Belgium

Tiny MPWScript

Here’s a tiny MPW script I find indispensible when collaborating on an MPW project. It lets you instantly open the files that your coworkers have changed.

The CheckOut command does have a -open option, but with this script you can choose which files to open and in what order, and you can wait until later to do it. Of course, once you have a file open you can use CompareRevisions to see what changed. Put this script in your MPW:Scripts folder and call it “Checked”. Opens the file referenced in the output of a projector CheckOut -p command:


/* 4 */
Checked out "HD:Blah:Blah.c,9" from "Blah ".

You can execute lines of this form directly from your worksheet (in groups or individually). This is an amazingly complicated script...not! It ignores its first argument, which is always “out”, its third argument, which is always “from”, and its fourth argument, which is the project pathname. All we care about is the second argument, which is almost the filename that we want the trick is ignoring the comma and digits at the end, which we do by matching the argument against a regular expression (see “help patterns”).


/* 5 */
(evaluate "{2}" =~ /( )®1,[0-9.]+/ ) > Dev:Null
open "{®1}"

Yes, it’s a two-line script.

- Dave Lyons

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Skateboard Party 3 ft. Greg Lutzka (Gam...
Skateboard Party 3 ft. Greg Lutzka 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Skateboard Party is back! This third edition of the popular sports franchise features professional skater... | Read more »
Cubious (Games)
Cubious 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: Cubious – How smart are you? How high is your IQube? Solve the impossible puzzles to find out, and help a lost little cube find his... | Read more »
Goat Simulator Waste of Space (Games)
Goat Simulator Waste of Space 1.1 Device: iOS Universal Category: Games Price: $4.99, Version: 1.1 (iTunes) Description: ** IMPORTANT - SUPPORTED DEVICESiPhone 4S, iPad 2, iPod Touch 5 or better.** | Read more »
Wildfulness - Unwind in nature and calm...
Wildfulness - Unwind in nature and calm your mind with nature sounds and illustrations 1.0 Device: iOS Universal Category: Healthcare & Fitness Price: $1.99, Version: 1.0 (iTunes) Description: Spending time in nature helps you to... | Read more »
Dr. Panda Racers (Education)
Dr. Panda Racers 1.0 Device: iOS Universal Category: Education Price: $2.99, Version: 1.0 (iTunes) Description: STEP ON THE GAS, RACE AND WIN!Fasten your seat belts and get ready to race! Speed your way to the finish line while doing... | Read more »
ROMANCING SAGA 2 (Games)
ROMANCING SAGA 2 1.0.0 Device: iOS Universal Category: Games Price: $17.99, Version: 1.0.0 (iTunes) Description: Romancing SaGa 2, originally released only in Japan in 1993, has been completely remastered and now receives its first... | Read more »
WRIO Keyboard (Utilities)
WRIO Keyboard 1.0 Device: iOS iPhone Category: Utilities Price: $2.99, Version: 1.0 (iTunes) Description: 40% OFF DURING LIMITED INTRODUCTORY OFFER | Read more »
Hatoful Boyfriend (Games)
Hatoful Boyfriend 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: The hit PC game that everybirdie loves has now migrated to your mobile device! Now you are free to explore the wonders of St... | Read more »
Warp Shift (Games)
Warp Shift 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: [ CHECK YOUR HARDWARE: Warp Shift does NOT run on iPhone 4, iPad 1 and iPod touch 4G or older devices! It requires at least iOS8... | Read more »
Lifeline: Whiteout (Games)
Lifeline: Whiteout 1.0.2 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0.2 (iTunes) Description: Alone in a frozen wasteland with no memory of how he got there, a lost adventurer’s only hope is his last line of... | Read more »

Price Scanner via MacPrices.net

Goal Zero and OtterBox Partner to Expand iPh...
Goal Zero, specialists in portable power, have announced a partnership with OtterBox, brand smartphone case protection, to offer the Slide and Slide Plus Batteries as modules compatible with the new... Read more
15-inch Retina MacBook Pros on sale for up to...
B&H Photo has 15″ Retina MacBook Pros on sale for up to $210 off MSRP. Shipping is free, and B&H charges NY tax only: - 15″ 2.2GHz Retina MacBook Pro: $1799 $200 off MSRP - 15″ 2.5GHz Retina... Read more
Clearance 2015 13-inch MacBook Airs available...
B&H Photo has clearance 2015 13″ MacBook Airs available for $250 off original MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 1.6GHz/4GB/128GB MacBook Air (MJVE2LL/A): $799... Read more
Apple refurbished Apple TVs available for up...
Apple has Certified Refurbished 32GB and 64GB Apple TVs available for up to $30 off the cost of new models. Apple’s standard one-year warranty is included with each model, and shipping is free: -... Read more
21-inch iMacs on sale for up to $120 off MSRP
B&H Photo has 21″ iMacs on sale for up to $120 off MSRP including free shipping plus NY sales tax only: - 21″ 3.1GHz iMac 4K: $1379.99 $120 off MSRP - 21″ 2.8GHz iMac: $1189 $110 off MSRP - 21″ 1... Read more
Kanex Introduces GoPower USB-C Rechargeable B...
Kanex has announced its GoPower USB-C portable battery for the USB-C MacBook, featuring the new industry standard connector and cable used for connectivity and power. Providing users with a new... Read more
Convertible and Detachable Devices Winning Ov...
According to the latest figures published by International Data Corporation (IDC), Western European shipments of ultraslim convertibles and detachables posted positive growth (44.7%) to account for... Read more
New MacBook Pros And Will MacBook Air Be Upgr...
With my mid-2013 13-inch MacBook Air closing on its third anniversary come November, I’m in system upgrade mode. Actually the Haswell CPU equipped Air is still doing a fine job, but my good wife is... Read more
Apple’s Education discount saves up to $300 o...
Purchase a new Mac or iPad using Apple’s Education Store and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free, and... Read more
13-inch 2.5GHz MacBook Pro on sale for $999,...
B&H Photo has the 13″ 2.5GHz MacBook Pro on sale for $999 including free shipping plus NY sales tax only. Their price is $100 off MSRP. Read more

Jobs Board

Editor, *Apple* News - APPLE (United States...
Job Summary The Apple News team is looking for a passionate and knowledgeable editor with experience covering entertainment/pop culture and experience running social Read more
*Apple* Nissan Service Technicians - Apple A...
Apple Automotive is one of the fastest growing dealer...and it shows. Consider making the switch to the Apple Automotive Group today! At Apple Automotive , Read more
ISCS *Apple* ID Site Support Engineer - APP...
…position, we are looking for an individual who has experience supporting customers with Apple ID issues and enjoys this area of support. This person should be Read more
Automotive Sales Consultant - Apple Ford Linc...
…you. The best candidates are smart, technologically savvy and are customer focused. Apple Ford Lincoln Apple Valley is different, because: $30,000 annual salary Read more
*Apple* Support Technician II - Worldventure...
…global, fast growing member based travel company, is currently sourcing for an Apple Support Technician II to be based in our Plano headquarters. WorldVentures is Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.