All Databases MacTech Vol 11-1995

Apr 95 Tips

Volume Number: 11

Issue Number: 4

Column Tag: Tips & Tidbits

Tips & Tidbits

By Scott T Boyd, Editor

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

source code disks.

TIP OF THE MONTH

Doing Passwords the Simple Way

A common problem for people writing multi-user software for the Mac is the

need to have a username/password dialog which allows the user to type the password

without actually printing the real characters. Apple’s inimitable Tim Dierks released

a snippet appropriately entitled “Password” which shows how to accomplish this in a

variety of ways, most of which involve keeping one buffer which holds what the user

actually types and another which contains the ‘display’ text (usually a line of bullets).

The following snippet shows how to accomplish this by replacing the QuickDraw

bottlenecks. The beauty of this approach is that there is no messy buffer-update code

needed for handling Cut/Copy/Paste, and text selection with the mouse is handled

correctly. You may, however, want to prevent people from cutting or copying text to

the clipboard, since if that text is pasted into any other TextEdit area it will display

the password in normal text.

#ifdef __cplusplus

extern "C" {
#endif
  PasswordDrawProc

void PasswordDrawProc (void)

        {
                Ptr textBuff;
                short byteOff;
                short byteCnt, i;

// load the correct parameters

                asm     {       move.l  A0, textBuff
                                move.w  D0, byteOff
                                move.w  D1, byteCnt
                        }

for (i = 1; i <= byteCnt; i++)

DrawChar ('•');

}

PasswordMeasureProc

void PasswordMeasureProc (void)

{

short textLen, offset;

Ptr textBuffer;

short width;

// load the correct parameters

                asm     {       move.w  D0, textLen
                                move.w  D1, offset

move.l A0, textBuffer

}

width = CharWidth('•') * textLen;

// return the width of the text

                asm     {       move.w  width, D1       }
        }

TEHandle MakePasswordTextBox (void)

{

Rect viewRect, destRect;

TEHandle textBlock = NULL;

SetRect (&viewRect, 15, 15, 165, 31);

SetRect (&destRect, 15, 15, 165, 31);

textBlock = TENew (&destRect, &viewRect);

if (textBlock)

{

TECustomHook (intDrawHook,

(ProcPtr)PasswordDrawProc, textBlock);

TECustomHook (intWidthHook,

(ProcPtr)PasswordMeasureProc, textBlock);

}

return textBlock;

}

#ifdef __cplusplus

}

#endif

- Eric Rosé, rose@nomos.com

SyncWait No More!

Sometimes when you’re AppleTalking or modeming and something goes wrong (like you

switch the modem off while data is being sent to it), the computer will hang. The mouse

will still move, but clicking will have no effect. Here’s the solution: Drop into

MacsBug. You should see the routine name “_vSyncWait” plus something as the

current location. If you don’t, you probably hit the system while it was doing

something else. Hit Command-G to get back out of MacsBug, and try again. After a few

tries you should find _vSyncWait.

_vSyncWait is the routine that the system uses to wait for some input from a

serial port. If you can read assembly code, you’ll see that it’s pretty simple. Here’s the

dump of the significant part:

+0000 4080BB8C MOVE.W $0010(A0),D0 | 3028 0010

+0004 4080BB90 BGT.S _vSyncWait ; 4080BB8C | 6EFA

when the awaited input arrives. The MOVE.W instruction grabs this word and puts it

into register D0. The BGT.S instruction then Branches back to the MOVE.W if the byte

it just fetched is Greater Than zero (hence BGT). So it happens that this byte is never

going to arrive for whatever reason, but the computer is going to wait for eternity. The

secret to fixing this is to use Command-T to go step along until the MOVE.W instruction

is displayed as the current instruction. Now use the “sw” command to set

“@(a0+10)” to zero: sw @(a0+10) 0

Then hit Command-T twice more. The MOVE.W instruction will take the zero you

just set into memory and put it in D0, so the D0 display on the right of the screen

should have its right four digits all zeros. Then when you execute the BGT.S

instruction, it should not go back to the MOVE.W since zero is not greater than zero.

Hit Command-G to go. If this was the only byte the software was waiting for, then

it should continue running, although it may go a little crazy because it’s been suddenly

disconnected from whatever peripheral it was talking to. Quit the program, fix your

hardware, and try again.

- Macneil Shonle and Dustin Mitchell

MacneilS@aol.com and DustyM2@aol.com

So Easy To Forget These Things

I asked the question recently, “When debugging using Think C, after hitting the

programmer’s switch and landing in MacsBug, how do I get back up to Think C’s source

level debugger?”

The answer, while less than what I was looking for, was nonetheless useful.

Think C’s debugger polls for Option-Command-Shift-Period. Use that instead of the

programmer’s switch and you will be able to break into the debugger as long as the

program is stuck in your own code, and not in the operating system somewhere.

- Jeffrey A. Lomicka, Marlboro MA, lomickaj@prnsys.enet.dec.com

What’ll They Call The Next One? Post-Modern Memory Manager?

So you’re trying to figure out whether a zone is a Modern Memory Manager zone?

Why? Oh, never mind, you’ve certainly got a good reason (you do, don’t you?), so

here’s how:

#define IsNewStyleZone(z)

((z)->heapType & 0x02)

if (IsNewStyleZone(LMGetSysZone()) {
   ...whatever...

- Dave Falkenburg, Apple

Referenced by (5):