TweetFollow Us on Twitter

XCMD Corner
Volume Number:4
Issue Number:7
Column Tag:HyperChat®

XCMD Corner

By Donald Koscheka, Apple Computers, Inc.

--Don Koscheka’s XCMD Corner

Last month I introduced XCMD programming. I explained the parameter block and discussed the interface between HyperTalk and the code that you write in either Pascal, “C” or the language of your choice. If you’re an experienced Macintosh programmer, that’s enough information to get started. The designers of HyperCard didn’t stop with just defining the interface for you. They went beyond what might be reasonably expected and provided some HyperTalk programming capabilities to the XCMD programmer. The XCMD programmer gains access to these capabilities through callbacks. Callbacks are procedures and functions that you call from your XCMD. Callbacks literally jump into Hypercard to perform some function.

Once you get the hang of XCMD programming, you’ll come to rely on some of the callbacks quite frequently. For example, Pascal programmers are accustomed to strings that are preceded by a length byte and that have a maximum of 255 characters (the Str255 type in Pascal) while HyperCard uses strings that have no length byte and are terminated with zero ( referred to as Zero-strings, zero-terminated strings or “C” strings). HyperTalk provides callbacks to convert from zero-terminated strings to Pascal and back again. The XCMD programmer can also use callbacks to retrieve and set the contents of fields and global containers as well as to send messages back to Hypercard.

One of the reasons that this access to HyperCard containers is so important is that XCMDs do not have access to the application globals. When Hypercard starts up, it takes control of its application globals and heap just as any application would. With Hypercard in control of the heap, your XCMD becomes a “guest” of Hypercard. You don’t have access to the globals from your XCMD so you’ll need a safe place to store information that you want to keep around.

A good candidate is a global container. Although Hypercard itself prefers to see text strings in containers, it’s not particular about what you put into a container; you can use the SetGlobal callback to put data into a global container, and GetGlobal to retrieve that data. Make sure that you declare any global containers in Hypercard before accessing them in an XCMD. Your XCMD may need to be backward compatible earlier versions of Hypercard that bombed if you called SetGlobal with an undeclared container name.

An interesting example of the use of callbacks is to send a card message back to HyperCard from a callback. The XCMD in listing 1, “SendMeAMessage”, takes one parameter which is the message to send back to HyperCard. Since messages are sent back as Pascal-format strings, we must convert the input string into a pascal string and then call SendCardMessage to send the message. As a matter of form, we set the return value to NIL indicating that this XCMD doesn’t have a result code (Hypercard will interpret NIL as empty).

The first callback that SendMeAMessage invokes, ZeroToPas, converts input parameter 1 from a zero-terminated string to a pascal-string. Input parameters are passed as handles so the parameter needs to be dereferenced one-time to convert the value to a pointer. ZeroToPas also expects you to pass a reference to the pascal-string into which you’ll store the converted Pascal-string. The second callback, SendCardMessage, sends the message back to Hypercard. To invoke this XCMD from a script use the form:

 SendMeAMessage “go next card”

Because Hypercard already handles message passing, this XCMD may not seem terribly useful. Nonetheless, it is a good illustration of callbacks and the technique is useful if you need to alert the user that some asynchronous event has completed.

{1}
{******************************}
{* File: SendMeAMessage.p *}
{******************************}
(******************************
 BUILD SEQUENCE
      (IGNORE LINK WARNINGS)
pascal SendMeAMessage.p
link -m ENTRYPOINT -rt XCMD=65534 
 -sn Main=SendMeAMessage 
 SendMeAMessage.p.o 
 “{Libraries}”Interface.o 
 “{PLibraries}”Paslib.o 
 -o “{xcmds}”testxcmds
******************************)

{$S SendMeAMessage }

UNIT Donald_Koscheka; 

{--------------INTERFACE----------------}
INTERFACE

USES  MemTypes, QuickDraw, OSIntf, ToolIntf, 
 PackIntf, HyperXCmd;

PROCEDURE EntryPoint( paramPtr: XCmdPtr);

{----------IMPLEMENTATION--------------}
IMPLEMENTATION
{$R-}
 
TYPE
 Str31  = String[31];
 
PROCEDURE SendMeAMessage(paramPtr:XCmdPtr);
 FORWARD;

{-------------- EntryPoint --------------}
PROCEDURE EntryPoint(paramPtr: XCmdPtr);
 BEGIN
 SendMeAMessage(paramPtr);
 END;

{------------ SendMeAMessage ------------}
PROCEDURE SendMeAMessage(paramPtr: XCmdPtr);
VAR
 theMessage : Str255;
 
{$I XCmdGlue.inc }
 
BEGIN {*** Body of XCMD ***}
 ZeroToPas( paramPtr^.params[1]^, theMessage );
 SendCardMessage( theMessage );
 paramPtr^.returnValue := NIL;
END; {*** Body of XCMD ***}
END.

Listing 1. SendACardMessage

XCMDs can also use callbacks to get the contents of a field or a global container. Listing 2, GetHomeInfo, uses two new callbacks (1) GetFieldByNum, to get the contents of background field 1 on the home card and (2) SetGlobal to set the contents of some global container.

GetHomeInfo Takes one parameter, the name of the global container to set. First, convert the parameter to a pascal-string. Next, use a series of callbacks to push the current card and go to the home stack. Once we get to the home stack, we call GetFieldByNum to get field data. The first parameter that GetFieldByNum takes is set to TRUE if you want to retrieve the contents of a card field and set to FALSE to retrieve the contents of a background field. The second parameter is the number of the field to retrieve. Alternatively, you could use GetFieldByID if you knew the id of the field or GetFieldByName if you knew the name.

GetFieldByNum returns a handle to the zero-terminated data that was stored in background field 1 of the home card. We then invoke SetGlobal to set the contents of the global container to whatever is stored in fieldData. Finally, we pop the current card to get back to where we started. A typical invocation of this XCMD is:


{2}
 global myData
 GetHomeInfo “myData”



PROCEDURE GetHomeInfo(paramPtr: XCmdPtr);
VAR
 globalName : Str255;
 fieldData: Handle;
 
{$I XCmdGlue.inc }
 
BEGIN
 WITH paramPtr^ DO
 BEGIN
 ZeroToPas( params[1]^, globalName );
 SendCardMessage( ‘Push Card’ );
 SendCardMessage( ‘Go Home’);
 
 fieldData := GetFieldByNum( FALSE, 1 );
 SetGlobal( globalName, fieldData );
 
 SendCardMessage( ‘Pop Card’);
 returnValue := NIL;
 END;
END;

Listing 2. Get Home Info.

So far I’ve showed you XCMDs that don’t do anything that you can’t already do in HyperTalk. A key feature of XCMD programming is that you can write your own commands to augment or add capabilities to Hypercard. Listing 3, “FCreateXFCN”, lets you create a file of any type from HyperCard. This XFCN demonstrates how XCMDs provide greater access to the toolbox than is available to the HyperTalk script writer.

FCreateXFCN introduces two new callbacks. NumToStr returns a result code to the script. NumToStr converts a signed long integer to a pascal-format string. If you don’t want a signed entity, use LongToStr instead which will convert the long integer without regard to sign.

The second callback introduced in this XFCN is PasToZero which takes a pascal format string and returns handle to a zero-terminated string. PasToZero is a handy way of copying from a pascal-string back to a zero-terminated string to return text to Hypercard.

I wrote the XFCN in “C” to show the difference in formats between Pascal and “C” XCMDS and to provide a template for “C” programmers. An important difference is that the parameter list, params, starts at index 0 for “C” and index 1 for Pascal.

FCreateXFCN first converts parameter 1 (params[0]) into a pascal-string and then moves the first four bytes of parameters 2 and 3 into the variables creator and type respectively. These two variables are of type OSType which is a special Macintosh type containing four consecutive ASCII characters. All four characters in this type are significant.

The result code will be empty if no error occurred and the file was created properly, otherwise it will return the OSErr number that occurred. First, convert the result code back to a pascal-string and then call PasToZero to convert that string into a handle to a zero-terminated string.

The XFCN would be more useful if it returned a brief description of the error in English, but I think I’ll leave that as an exercise for the student. Call FCreateXFCN with the following script:

Put FCreateXFCN( “New File Name”, “WILD”,  “STAK” )

The first parameter is the name of the file you wish to create, the second parameter is the creator and the last parameter is the file type. The foregoing invocation will create an empty stack. What can you do with that?

{3}
/*****************************\
*file: FCreateXFCN.c *
\*****************************/

/*****************************
 BUILD SEQUENCE
 
C -q2 -g FCreateXFCN.c
link  -sn Main=FCreateXFCN 
 -sn STDIO=FCreateXFCN 
  -sn INTENV=FCreateXFCN 
  -rt XFCN=300 
  -m FCREATEXFCN 
  FCreateXFCN.c.o 
  “{CLibraries}”CInterface.o 
  -o testXCMDs
 
*****************************/
#include<Types.h>
#include<OSUtils.h>
#include<Memory.h>
#include<Files.h>
#include<Resources.h>
#include  “HyperXCmd.h”

pascal void FCreateXFCN( paramPtr )
 XCmdBlockPtr  paramPtr;
/****************************
* In:   Paramblock:
*param[0] == filename
*param[1] == TYPE
*param[2] == CREATOR
* Out:  result code in returnValue
****************************/
{
char    *fname;
OSType  type, creator;
Str31 str;
char    vName[33];
short   error, vRefnum;

/** coerce the volume reference  ***
***number from the system **/
GetVol( vName, &vRefnum );
 
/**extract the filename from  ***
***the parameter list     **/
fname   = *(paramPtr->params[0]);
BlockMove(*(paramPtr->params[1]),&creator,4 );
BlockMove(*(paramPtr->params[2]),&type,4 );
 
error = Create( fname, vRefnum, 
 creator, type );
 
FlushVol( 0L, vRefnum );
 
if( !error )
 paramPtr->returnValue = 0L;
else{
 NumToStr( paramPtr, (long)error, &str );
 paramPtr->returnValue = 
 PasToZero( paramPtr, &str );
 }
}

#include <XCmdGlue.inc.c>

Listing 3. FCreateXFCN

Although this article covered some of the more frequently used callbacks, my objective was to present you with the spirit of the callback mechanism. You should have no trouble using any of the callbacks that are currently defined in the HyperCard Developer’s ToolKit (available from APDA). The most important lesson here is that before you go off and write an XCMD, check the callback list to see how you might incorporate them into your XCMDs. Try to get the callbacks to do as much work as possible for you so that you can concentrate on the code that you are trying to write.

Next Month: SortList, an XCMD that sorts a field by line.

end HyperChat
 

Community Search:
MacTech Search:

Software Updates via MacUpdate

GIMP 2.8.14p2 - Powerful, free image edi...
GIMP is a multi-platform photo manipulation tool. GIMP is an acronym for GNU Image Manipulation Program. The GIMP is suitable for a variety of image manipulation tasks, including photo retouching,... Read more
Sandvox 2.10.2 - Easily build eye-catchi...
Sandvox is for Mac users who want to create a professional looking website quickly and easily. With Sandvox, you don't need to be a Web genius to build a stylish, feature-rich, standards-compliant... Read more
LibreOffice 5.0.1.2 - Free, open-source...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
f.lux 36.1 - Adjusts the color of your d...
f.lux makes the color of your computer's display adapt to the time of day, warm at night and like sunlight during the day. Ever notice how people texting at night have that eerie blue glow? Or wake... Read more
VirtualBox 5.0.2 - x86 virtualization so...
VirtualBox is a family of powerful x86 virtualization products for enterprise as well as home use. Not only is VirtualBox an extremely feature rich, high performance product for enterprise customers... Read more
File Juicer 4.43 - Extract images, video...
File Juicer is a drag-and-drop can opener and data archaeologist. Its specialty is to find and extract images, video, audio, or text from files which are hard to open in other ways. In computer... Read more
Apple MainStage 3.2 - Live performance t...
MainStage 3 makes it easy to bring to the stage all the same instruments and effects that you love in your recording. Everything from the Sound Library and Smart Controls you're familiar with from... Read more
formZ 8.5 - Solid and surface modeler. (...
formZ pro is a powerful 3D design application featuring a variety of modeling personalities and tools with an easy to use interface to express and communicate your imagination. It is based on... Read more
PopChar 7.2 - Floating window shows avai...
We're also selling a 5-license family pack for only $25.99! PopChar helps you get the most out of your font collection. With its crystal-clear interface, PopChar provides a frustration-free way to... Read more
FileMaker Pro 14.0.2 - Powerful, easy-to...
FileMaker Pro is powerful, easy-to-use software used to create custom solutions for your business that run on iPad, iPhone, Windows, Mac and the web. Use FileMaker Pro to manage and share information... Read more

ReBoard: Revolutionary Keyboard (Utilit...
ReBoard: Revolutionary Keyboard 1.0 Device: iOS Universal Category: Utilities Price: $1.99, Version: 1.0 (iTunes) Description: Do everything within the keyboard without switching apps! If you are in WhatsApp, how do you schedule a... | Read more »
Tiny Empire (Games)
Tiny Empire 1.1.3 Device: iOS Universal Category: Games Price: $2.99, Version: 1.1.3 (iTunes) Description: Launch cannonballs and blow tiny orcs into thousands of pieces in this intuitive fantasy-themed puzzle shooter! Embark on an... | Read more »
Astropad Mini (Productivity)
Astropad Mini 1.0 Device: iOS iPhone Category: Productivity Price: $4.99, Version: 1.0 (iTunes) Description: *** 50% off introductory price! ​*** Get the high-end experience of a Wacom tablet at a fraction of the price with Astropad... | Read more »
Emo Chorus (Music)
Emo Chorus 1.0.0 Device: iOS Universal Category: Music Price: $1.99, Version: 1.0.0 (iTunes) Description: Realistic Choir simulator ranging from simple Chorus emulation to full ensemble Choir with 128 members. ### introductory offer... | Read more »
Forest Spirit (Games)
Forest Spirit 1.0.5 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0.5 (iTunes) Description: | Read more »
Ski Safari 2 (Games)
Ski Safari 2 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: The world's most fantastical, fun, family-friendly skiing game is back and better than ever! Play as Sven's sister Evana, share... | Read more »
Lara Croft GO (Games)
Lara Croft GO 1.0.47768 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0.47768 (iTunes) Description: Lara Croft GO is a turn based puzzle-adventure set in a long-forgotten world. Explore the ruins of an ancient... | Read more »
Whispering Willows (Games)
Whispering Willows 1.23 Device: iOS Universal Category: Games Price: $4.99, Version: 1.23 (iTunes) Description: **LAUNCH SALE 50% OFF** - Whispering Willows is on sale for 50% off ($4.99) until September 9th. | Read more »
Calvino Noir (Games)
Calvino Noir 1.1 Device: iOS iPhone Category: Games Price: $3.99, Version: 1.1 (iTunes) Description: The film noir stealth game. Calvino Noir is the exploratory, sneaking adventure through the 1930s European criminal underworld.... | Read more »
Angel Sword (Games)
Angel Sword 1.0 Device: iOS Universal Category: Games Price: $6.99, Version: 1.0 (iTunes) Description: Prepare to adventure in the most epic full scale multiplayer 3D RPG for mobile! Experience amazing detailed graphics in full HD.... | Read more »

Price Scanner via MacPrices.net

Tablet Screen Sizes Expanding as iPad Pro App...
Larger screen sizes are gaining favor as the tablet transforms into a productivity device, with shipments growing 185 percent year-over-year in 2015. According to a new Strategy Analytics’ Tablet... Read more
Today Only: Save US$50 on Adobe Elements 13;...
Keep the memories. lose the distractions. Summer’s winding down and it’s time to turn almost perfect shots into picture perfect memories with Elements 13. And get the power to edit both photos and... Read more
1.4GHz Mac mini on sale for $449, save $50
Best Buy has the 1.4GHz Mac mini on sale for $50 off MSRP on their online store. Choose free shipping or free local store pickup (if available). Price for online orders only, in-store price may vary... Read more
12-inch 1.1GHz Gold MacBook on sale for $1149...
B&H Photo has the 12″ 1.1GHz Gold Retina MacBook on sale for $1149.99 including free shipping plus NY sales tax only. Their price is $150 off MSRP, and it’s the lowest price available for this... Read more
27-inch 3.3GHz 5K iMac on sale for $1849, sav...
Best Buy has the 27″ 3.3GHz 5K iMac on sale for $1849.99. Their price is $150 off MSRP, and it’s the lowest price available for this model. Choose free shipping or free local store pickup (if... Read more
Worldwide Tablet Shipments Expected to Declin...
Does Apple badly need a touchscreen convertible/hybrid laptop MacBook? Yes, judging from a new market forecast from the International Data Corporation (IDC) Worldwide Quarterly Tablet Tracker, which... Read more
Continued PC Shipment Shrinkage Expected Thro...
Worldwide PC shipments are expected to fall by -8.7 percent in 2015 and not stabilize until 2017, according to the latest International Data Corporation (IDC) Worldwide Quarterly PC Tracker data. The... Read more
Imminent iPhone 6s Announcement Leads To 103%...
NextWorth Solutions, with its online and in-store electronics trade-in programs including http://NextWorth.com, reports that it has experienced a 103 percent surge in quoted trade-in values over the... Read more
Weekend Deal: 13-inch Retina MacBook Pros for...
Save up to $100 on the purchase of a new 2015 13″ Retina MacBook Pro at the following resellers this weekend. Shipping is free with each model: 2.7GHz/128GB MSRP $1299 2.7GHz/... 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 $999.99 including free shipping plus NY sales tax only. Their price is $100 off MSRP. Read more

Jobs Board

*Apple* Solutions Consultant - Retail Sales...
**Job Summary** As an Apple Solutions Consultant (ASC) you are the link between our customers and our products. Your role is to drive the Apple business in a retail Read more
Product Design Engineer - *Apple* Watch - A...
**Job Summary** Product Design Engineer Job Description As a member of Apple 's Watch product design team, you will help to create the next generation of the world's Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
Software QA Engineer, *Apple* Pay Security...
Changing the world is all in a day039s work at Apple . If you love innovation, here039s your chance to make a career of it. You039ll work hard. But the job comes with Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.