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Finder Strings
Volume Number:9
Issue Number:4
Column Tag:Fun Hacks

Related Info: Finder Interface

Rändóm fiNdEr sgnirtS

A cute extension to help you with April Fools Day

By By Mike Scanlin, MacTech Magazine Regular Contributing Author

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

Recently at a friend’s house I saw a clock that ticks backwards. The whole thing looks like a normal clock would when viewed in a mirror. I thought to myself “Not very useful, is it? Kind of difficult to figure out what time it is. What if everything was backwards: newspapers, controls on my car, file names in the Finder... <click> Hey! Cool idea for an April Fool’s INIT.” And, so, here we are.

RandomFinderStrings is an INIT (Extension) that causes one of several effects to happen to each string drawn by the Finder: (1) the case of the letters is forced to be upper, lower, reversed or random, (2) the letters in the string are rearranged back-to-front, (3) all vowels get an accent mark or (4) all vowels are removed. The effect that happens to each string is random. The framework of the code has been set up to make it easy to add your own effects if you can think of a cool way to tweak a Str255 (maybe you could do a conversion to Pig Latin or something) or, you can just use the code as it appears here. You can have some fun if you give this INIT an unsuspecting name like “Easy Access” and put it on a [former?] friend’s Mac.


The first part of the INIT code creates space for the patch and effects code in the system heap (about 800 bytes) and moves a copy of the code there. Then it installs a head patch on DrawString. The patched DrawString will first check if CurApName == “\pFinder” and that the Option key is not down. If both conditions are true then it will randomly change a copy of the string before calling the real DrawString to draw the string. Note that comment about the Option key. If you really need to see the true strings once this INIT is installed, and you can’t afford to remove it and reboot, you can hold down the Option key and cause the screen to refresh (with a screen saver)-everything will redraw normally (but if you let go of the option key then things begin to get drawn tweaked again).


Here are some screen shots that show some of the effects this INIT is capable of. Figure 1 shows the System Folder when ACCENTED_VOWELS is on, figure 2 shows the About This Macintosh box when BACKWARDS_LETTERS is on and, figure 3 shows the File menu when DO_CASE_CHANGES is on (the NO_VOWELS option isn’t shown here). You can mix and match these effects until you reach the level of annoyance you desire but you will have to recompile each time you change which effects are on/off. You turn them off by setting their #defined values to 0 and you turn them on by setting their #defined values to 1. If ALWAYS_TWEAK_STRING is off (i.e. zero) then not every string drawn by the Finder will be modified (because of the -1 case in the main switch statement).

Figure 1

Figure 2

Figure 3

Except for maybe the trap patching, this code is pretty easy to understand. The actual effects that tweak the copy of the string are rather simple. One thing to note might be the politically correct way to check if the Option key is down at a time when we don’t have an EventRecord: We make a dummy event record and call OSEventAvail with a mask of zero. This is a much better method than using GetKeys.

Because this is an INIT, the Think C Project Type should be “Code Resource” and the File Type should be “INIT”. You can use whatever you want for the Creator and ID (I used “Twen” with an ID of 55). Have fun.

 * RandomFinderStrings.c
 * This INIT installs a patch on DrawString that will tweak 
 * strings drawn by the Finder. If CurApName != “/pFinder” 
 * or if the option key is down then a normal DrawString 
 * takes place. If we are in the Finder then a modified 
 * version of the string is drawn: the upper/lower case of 
 * the letters might be changed, the string might be flipped 
 * backwards, all the vowels might get accent marks, etc.
 * You can add to the list of effects by adding an item to 
 * the Effects enum and the main switch statement in 
 * MyDrawString. If your effects need globals, put them in 
 * the PatchGlobals struct and initialize them in main.
 * In Think C, set the Project Type to Code Resource, the 
 * File Type to INIT, the Creator to anything, the Type to 
 * INIT, the ID to something like 55 (55 will work but it
 * doesn’t have to be 55), turn Custom Header ON and Attrs 
 * to 20 (purgeable) and Multi Segment OFF.
 * Mike Scanlin. 24 Jan 1993.
 * defines
#define _DrawString         0xA884

enum Effects {
    UpperCase = 0,
    NumEffects /* must be last */

/* Turn these all on for maximum randomness */
#define DO_CASE_CHANGES     1
#define ACCENTED_VOWELS     1
#define NO_VOWELS           1
#define PIG_LATIN           0


    /* Generate a compile time error if you set up an 
     * impossible situation. You need to have at least one 
     * effect enabled if ALWAYS_TWEAK_STRING is enabled. */

 * typedefs
typedef pascal void (*DSProcPtr)(Str255 *theStringPtr);

typedef struct PatchGlobals {
    DSProcPtr       pgOldDS;
} PatchGlobals, *PatchGlobalsPtr;

 * prototypes
void main(void);
void StartPatchCode(void);
pascal void MyDrawString(Str255 *theStringPtr);
short abs(short n);
void EndPatchCode(void);

/******************** main ***********************
 * Gets some memory in the system heap and installs the 
 * DrawString patch (as well as allocating and initializing 
 * the patch globals).  This is the only routine that gets 
 * executed at startup time (by the INIT mechanism).
 * The block of memory that main allocates will
 * look like this when main has finished:
 *                   +--------------------+
 *                   |    PatchGlobals    |
 *                   +--------------------+
 *                   |  StartPatchCode()  |
 *   DS trap addr -> +--------------------+
 *                   |   MyDrawString()   |
 *                   +--------------------+
 *                   |       abs()        |
 *                   +--------------------+
 *                   |   EndPatchCode()   |
 *                   +--------------------+
void main()
    Ptr             patchPtr;
    PatchGlobalsPtr pgPtr;
    long            codeSize, offset;
    /* try and get some memory in the system heap
     * for code and globals */
    codeSize = (long) EndPatchCode -
        (long) StartPatchCode;
    patchPtr = NewPtrSys(codeSize +
    if (!patchPtr)
        return; /* out of memory-abort patching */
    /* initialize the patch globals at the
     * beginning of the block */
    pgPtr = (PatchGlobalsPtr) patchPtr;
    pgPtr->pgOldDS = (DSProcPtr)
    /* move the code into place after the globals */
    BlockMove(StartPatchCode, patchPtr +
        sizeof(PatchGlobals), codeSize);
    /* set the patches */
    patchPtr += sizeof(PatchGlobals);
    offset = (long) MyDrawString -
        (long) StartPatchCode;
    SetTrapAddress((long) patchPtr + offset,

/***************** StartPatchCode ****************
 * Dummy proc to mark the beginning of the code 
 * for the patches. Make sure all of your patch
 * code is between here and EndPatchCode.
void StartPatchCode()

/*********************** MyDrawString **********************
 * Head patch on DrawString that randomly tweaks the string 
 * to be drawn if the current application is the Finder and 
 * the Option key is not down.
pascal void MyDrawString(Str255 *theStringPtr)
    Str255          copyOfString;
    EventRecord     theEvent;
    PatchGlobalsPtr pgPtr;
    Byte            *p, *inputPtr;
    short           rand;
    Byte            i, ch;
    /* if we’re not in the Finder then exit */
    if (*(char *) &CurApName != 6 ||
      *(long *) ((Ptr) &CurApName + 1) != ‘Find’ ||
      *(short *) ((Ptr) &CurApName + 5) != ‘er’ )
        goto DontDoAnything;
    /* if the option key is down then exit */
    OSEventAvail(0, &theEvent);
    if (theEvent.modifiers & optionKey)
        goto DontDoAnything;
    /* we’re in the Finder so do something to a
     * copy of the string (unless it’s zero-length) */
    if (i = *(Byte *) theStringPtr) {
        p = (Byte *) &copyOfString;
        BlockMove(theStringPtr, p++, i + 1);


        switch (abs(Random()) % NumEffects) {
        case UpperCase:
            /* force all letters to upper case */
            do {
                if (*p >= ‘a’ && *p <= ‘z’)
                    *p -= ‘a’ - ‘A’;
            } while (-i);
        case LowerCase:
            /* force all letters to lower case */
            do {
                if (*p >= ‘A’ && *p <= ‘Z’)
                    *p += ‘a’ - ‘A’;
            } while (-i);
        case ReverseCase:
            /* flip the upper/lower case of each letter */
            do {
                if (*p >= ‘a’ && *p <= ‘z’)
                    *p -= ‘a’ - ‘A’;
                else if (*p >= ‘A’ && *p <= ‘Z’)
                    *p += ‘a’ - ‘A’;
            } while (-i);
        case RandomCase:
            /* randomly set the case of each letter */
            do {
                /* force to lower case */
                if (*p >= ‘A’ && *p <= ‘Z’)
                    *p += ‘a’ - ‘A’;
                /* make half of them upper case */
                if (*p >= ‘a’ && *p <= ‘z’ && Random() < 0)
                    *p -= ‘a’ - ‘A’;
            } while (-i);

        case BackwardsLetters:
            /* flip the string front to back */
            inputPtr = (Byte *) theStringPtr + i;
            do {
                *p++ = *inputPtr;
            } while (-i);

        case AccentedVowels:
            /* put an accent mark over each vowel */
            do {
                rand = abs(Random());
                switch (*p) {
                case ‘A’:
                    switch (rand & (4-1)) {
                    case 0: *p = 0x80; break;
                    case 1: *p = 0x81; break;
                    case 2: *p = 0xCB; break;
                    case 3: *p = 0xCC; break;
                case ‘E’:
                    *p = 0x83;
                case ‘O’:
                    if (Random() < 0)
                        *p = 0x85;
                        *p = 0xCD;
                case ‘U’:
                    *p = 0x86;
                case ‘a’:
                    *p = 0x87 + (rand % 6);
                case ‘e’:
                    *p = 0x8E + (rand & (4-1));
                case ‘i’:
                    *p = 0x92 + (rand & (4-1));
                case ‘o’:
                    *p = 0x97 + (rand % 5);
                case ‘u’:
                    *p = 0x9C + (rand & (4-1));
            } while (-i);

        case NoVowels:
            /* remove all vowels */
            inputPtr = (Byte *) theStringPtr + 1;
            do {
                ch = *inputPtr;
                if (ch >= ‘A’ && ch <= ‘Z’)
                    ch += ‘a’ - ‘A’;
                if (ch == ‘a’ || ch == ‘e’ || ch == ‘i’
                  || ch == ‘o’ || ch == ‘u’)
                    *p++ = *inputPtr;
            } while (-i);
            /* make sure the string length is at least 1 */
            if (copyOfString[0] == 0) {
                copyOfString[0] = 1;
                copyOfString[1] = 
 *((Byte *) theStringPtr + 1);

        case PigLatin:
            /* not implemented */

        case -1:                    
            goto TryAgain;
        theStringPtr = &copyOfString;

    /* find our globals */
    pgPtr = (PatchGlobalsPtr) ((long) StartPatchCode -

    /* call the real DrawString */

/********************* abs **********************
 * Return the absolute value of n.
abs(short n)
    if (n < 0)
        return (-n);
    return (n);

/******************* EndPatchCode ********************
 * Dummy proc to mark the end of the code for
 * the patches. Make sure all of your patch code
 * is between here and StartPatchCode.
void EndPatchCode()


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