TweetFollow Us on Twitter

Playing sound
Volume Number:7
Issue Number:1
Column Tag:XCMD Corner

Playing With Sound

By Donald Koscheka, Contributing Editor

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

The Importance of XCMDs

One of the questions that is raised by Hypercard 2.0’s new XCMD interface is, “How important are XCMDs to the vitality of the Macintosh?”. One cannot imagine that XCMDs would be very important at all so it would be useful to the xcmd programmer to ponder the future of xcmds in the Macintosh programming world.

After studying Hypercard 2.0 in great detail, I’ve concluded that XCMDs are very important to the success of this product and that Apple Computer, Inc. is acknowledging this by providing more services to the XCMD programmer such as windoids and script manipulation capability. But another event in the small computer world lends even more credence to XCMD as programming art. That event is quietly taking over the MS-DOS world as Microsoft successfully evangelizes the concept of Dynamic Link Libraries, or DLLs.

If you’re not a PC programmer (and who can afford not to be), then you may not know that DLLs are code modules that are written in such a way as to be loadable and thus callable at any time. DLLs are code segments that have a standard programming interface associated with them. In effect, DLLs allow you to build re-usable code modules that in theory can be used in any application. Well, if every application had such an interface on the Mac, let’s call it XCmdPtr, then xcmds would serve the same purpose -- the ability to call xcmds from any program that runs on the mac. Without a lot of induction, one can come to the conclusion that if xcmds can give you this type of capability on the Mac, then they are indeed important, at least at the conceptual level.

If xcmds become callable from any application then they become an integral part of the future of the Macintosh. It is not unimaginable to believe that someday you will flesh-out your application with some sort of screen generator and then build a set of xcmds to implement the application-specific code. I find it impossible to believe that this effective approach to programming won’t become the norm for all programmers in the future. In fact, Michael Swain suggests exactly this approach for PC programmers using ToolBook ( “Dr. Dobbs Journal”, November, 1990). When I read this column, my eyes popped out of my head. Mr. Swain’s concept of marrying rapid prototyping with rapid code development via DLL’s is exactly what we’ve been doing with Hypercard for the last three years. Any Windows developer that takes his advice will wonder what all the fuss was about; Windows will appear to be an easy and natural development environment.

So now I can rest easy. I am convinced that the XCMD approach to programming will prevail over time. It’s working for me. By forcing me to avoid globals and to think modularly, XCMDs have allowed me to write code that is re-usable in a wide-variety of applications. Each time I write an XCMD, I create a piece of code that I not only know I will use again but that I can comfortably extract from Hypercard without worrying about breaking it. That is the programmer’s holy grail and that is why XCMDs not only have a future, they are the future.

Playsound

Several months ago, I got a call from Bill Leitman, a fellow Mac developer in the New York area. He was working with a small film company in Brooklyn that needed an xcmd that played a portion of a sound resource. Bill’s approach was quite reasonable, he took a piece of code that he knew to be working from another application and dropped it into an xcmd. Lo and behold, it didn’t work. He called me in desperation to see if there was anything that I knew about xcmds that was causing his problem. To no avail, I also tried to get the sound manager to work from within an xcmd but after hours of head scratching and staring at TMON windows, I came to the conclusion that Hypercard just wasn’t going to let me use the sound manager.

This was unfortunate and unbelievable, but I’ve never been able to find a way to get the sampled synth playing in an xcmd. Imagine my surprise when I first encountered the following callbacks in Hypercard 2.0: BEGINXSOUND and ENDXSOUND. Is it possible that it wasn’t me? Did Hypercard actually work the way I thought it did by taking over the sound driver and not making it available to anyone else. I don’t know the answer to this question, ‘tho I’d like to so please write if you have some input. I do know that this must have been a problem since Apple went to the motions of adding these callbacks, which work quite perfectly for me.

This month’s playsound xcmd (listing 1) was inspired by Mr. Leitman and I am grateful to him that he gave me an excuse to explore the sound manager. It’s more daunting than the Sunday Times crossword puzzle and just as much fun!

Playsound takes up to four parameters: the first is the name of the file to retrieve the sound resource from. The second parameter is the name of the sound resource to retrieve. The third parameter is the index to the sample to start playing from (0 means play from the beginning of the sound). The fourth parameter is the last sample to play to. These last two parameters are optional, if they are left out, the entire sound resource will be played.

For simplicity, this code makes two assumptions that you can modify to meet your own needs: (1) you want to play the sound using the sampled synthesizer and (2) the sound is a format 2 ‘snd ‘ resource. I chose not to support format 1 ‘snd ‘ resources because Inside Macintosh indicates that format 2 snd resources should be adopted by developers as a standard. Should you decide that you want to support format 1 resources, refer to page 491 of Inside Macintosh Volume V for details on that format.

The xcmd parses out the parameters, opens the appropriate resource file and loads the ‘snd ‘ resource which it then detaches from the resource map. This is important because we are going to modify the resource and we don’t want the changes to be written back out by mistake. We call BEGINXSOUND to advise hypercard that we want to take over the sound drive for a while. Next we call PlayRunSound to play the sound, or sound fragment, and then we call ENDXSOUND to give the sound driver back to Hypercard.

PlayRunSound() is the heart and soul of this xcmd. The first thing that it does is check to see if the appropriate synthesizer is available. If so, it then allocates a new channel via the SndNewChannel call. This call returns a pointer to our new channel, initialized for the sampled synthesizer in theChan. We will pass this pointer to SndDoCommand to play this sound on that channel.

Once the channel is initialized and we know that we can use it, we set the start and stop time of the sound and play it. The first thing we need to do is check to see if we have the correct resource format which we do by testing to make sure that the first word in the resource (sndHdl) is set to 2. If it is, then we can access the fields in the snd resource by referring to the documentation on page 494 of IM vol V.

Figure 1. A typical format 2 ‘snd ‘ resource.

Here is how the sound fragment scheme works: The snd resource contains some header information (6 bytes) followed by a number of 8 byte sound commands (the sample sound resource in figure 1 contains only one sound command). The sound data immediately follows the sound commands. If there is only one sound command, then the sampled data table will begin at offset 14 (0x0E) in the record.

The first two long words in the sound data table tell us where the samples start and how many of them there are. The where is usually set to 0 and the how much is usually set to the number of samples to play back. We can modify these fields to change the starting point and the number of samples to play. Or, we can set just the new starting point and play back to the end of the sound. Playsound doesn’t use the sound command (in this case, ‘soundCmd’) but rather uses the ‘bufferCmd’ instead.

So, we modify the sound table by stuffing new values for the pointer and length and then call the sound manager via the bufferCmd. Once the sound is done playing, we call SndDisposeChannel to remove our allocated channel, in effect freeing up the sampled synthesizer in preparing to give it back to Hypercard. That’s all there is to it. You might want to use this xcmd to continue to explore the sound manager. It appears to have rich and intriguing repertoire. In fact, I hope to present more on the sound manager in the future. In the meantime, I will continue to illuminate Hypercard 2.0. Happy Hacking.

Listing 1:  PlaySndFrag.c
/********************************/
/* File: PlaySndFrag.c    */
/********************************/
#define UsingHypercard

#include  <SoundMgr.h>
#include<SetupA4.h>
#include  <HyperXCmd.h>
/* usage: playSndFrag fileName, soundName, start ,stop
 project requires the following files or libraries:
 ANSI-A4-- the A4 based standard “C” libraries
 HyperXLib-- the xcmd callback glue
 MacTraps -- what it is
 PlaySnd.c-- this file */
 
void    putResult( XCmdPtr pp, char *msg);
void  PlayRunSound( Handle sndHdl, long start, long stop );
long  paramtoNum( XCmdPtr pp, short i );
void  paramtoPString( XCmdPtr pp, short i, char *str );
Handle  strToParam( char  *str );

#ifndef NIL
 #defineNIL (void *)0L
#endif

pascal void main( XCmdPtr pp )
/******************************************
* The main entry point 
******************************************/
{
 short resFile;  /*** resource file holding ‘snd ‘ ***/
 short saveResFile; /*** previous resource file id ***/
 Handle sndHdl; /*** handle to the sound resource ***/
 long start; /*** start sample in sound ***/
 long stop; /*** end sample in sound ***/
 char  *temp[256]; 
 /*** for converting to pascal strings ***/
   
 pp->returnValue = NIL;  /* empty return means OK */
 if (pp->paramCount == 1){
 if ( **(pp->params[0]) == ‘!’ ){
 pp->returnValue = strToParam(“Play Sound XCMD, version 1.0, ©Donald 
Koscheka, 1990”);
 return;
 }
 
 if ( **(pp->params[0]) == ‘?’ ){
 pp->returnValue = strToParam(“PlaySound FILE, ‘snd ‘ rsrc id [,start][,stop]”);
 return;
 }
 }

 paramtoPString( pp, 0, (char *)&temp );           
 start  = paramtoNum( pp, 2 );
 stop   = paramtoNum( pp, 3 );
  
 saveResFile = CurResFile(); /* save current res file id */
 resFile = OpenResFile( temp );
  
 if (resFile == -1) {
 putResult( pp, “can’t open resource file” );
 return;
 }
 
 UseResFile( resFile );  /* in case it was already open */
 paramtoPString( pp, 1, (char *)&temp );
 sndHdl = Get1NamedResource( ‘snd ‘, &temp );
 /* getting the resource ok */
 
 if(!sndHdl){
   putResult( pp, “no such snd” );
 UseResFile( saveResFile ); 
   return;
 }
 
   BEGINXSOUND( pp, NIL );
 DetachResource( sndHdl );
    PlayRunSound( sndHdl, start, stop );
 DisposHandle( sndHdl );
    ENDXSOUND( pp );
    
 UseResFile( saveResFile ); 
}
 
void  PlayRunSound( sndHdl, start, stop )
 Handle sndHdl;
 long   start;
 long stop;
/**********************************
* st[0] determines whether we have a
* format 2 or a format 1 ‘snd ‘ resource.    
* currently use the 44K sampler. Refer to Inside Macintosh Vol V p.494 
for the format of a format 2 ‘snd ‘ resource
**********************************/
{
    short *st;
    long  *lt;
    SndCommand   sndCmd;
   long idx;
 SndChannelPtr theChan  = NIL;
 OSErr    err;
   
 sndCmd.cmd = availableCmd;
 
 if( err = SndControl( sampledSynth, &sndCmd ) ) return;
 if( err = SndNewChannel( &theChan, sampledSynth, initSRate44k, NIL ) 
) return; 
  
 HLock( sndHdl );
   st = (short *)*sndHdl;
 sndCmd.cmd = bufferCmd;
   sndCmd.param1 = 0L;
 if( *st == 2){
 idx  = 6L + ((long)st[2] << 3);
 /* offset to start of commands    */
 lt     = *sndHdl + idx;
   sndCmd.param2 = (long)lt;
   
   if( start )
   lt[0]= (long)*sndHdl + idx + start; 
   
   if( stop )
        lt[1]  = stop  - start;  
        
 err = SndDoCommand( theChan, &sndCmd, FALSE );
   err = SndDisposeChannel( theChan, FALSE );
 }
 HUnlock( sndHdl );
}
 
void putResult( XCmdPtr pp , char *msg )
{
   if (pp->returnValue)   
 DisposHandle(pp->returnValue);  
 
   pp->returnValue = (Handle)NewHandle(1 + strlen(msg) );
   strcpy( *(pp->returnValue), msg);
}
 
Handle  strToParam( char  *str )
/***************************
* Given a pointer to a string, copy that string into a handle
* and return the handle.
* The input and output strings are both null-terminated
***************************/
{
 Handle outH = NIL;
 long len = 0;
 
 len = strlen( str );
 if( len )
 if( outH = NewHandle( len ) )
 BlockMove( str, *outH, len + 1 );
 return( outH );
}

void  paramtoPString( XCmdPtr pp, short i, char *str )
/************************
* Given an index into the parameter list, convert the data
* in the Block into a pstring
*
* This sequence is so common in XCMDs that it makes sense to make it 
a subr. This is a generic routine that you can use in any xcmd.
************************/
{
 if( pp->params[i] ){
 HLock( pp->params[i] );
 ZEROTOPAS( pp, (Ptr)*(pp->params[i]), (StringPtr)str );
 HUnlock( pp->params[i] );
 }
 else
 *str = ‘\0’;
}

long  paramtoNum( XCmdPtr pp, short i )
/************************
* Given a Block to an input argument in the paramBlk
* return an integer representation of the data.
************************/
{
 char   theStr[32];
 
 theStr[0] = ‘\0’;
 if( pp->params[i] ){
 HLock( pp->params[ i ] );
 ZEROTOPAS( pp, (char *)*(pp->params[ i ]), theStr );
 HUnlock( pp->params[ i ] );
 return STRTOLONG( pp, theStr );
 }
 return 0L;
}

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Latest Forum Discussions

See All

Top Mobile Game Discounts
Every day, we pick out a curated list of the best mobile discounts on the App Store and post them here. This list won't be comprehensive, but it every game on it is recommended. Feel free to check out the coverage we did on them in the links... | Read more »
Price of Glory unleashes its 1.4 Alpha u...
As much as we all probably dislike Maths as a subject, we do have to hand it to geometry for giving us the good old Hexgrid, home of some of the best strategy games. One such example, Price of Glory, has dropped its 1.4 Alpha update, stocked full... | Read more »
The SLC 2025 kicks off this month to cro...
Ever since the Solo Leveling: Arise Championship 2025 was announced, I have been looking forward to it. The promotional clip they released a month or two back showed crowds going absolutely nuts for the previous competitions, so imagine the... | Read more »
Dive into some early Magicpunk fun as Cr...
Excellent news for fans of steampunk and magic; the Precursor Test for Magicpunk MMORPG Crystal of Atlan opens today. This rather fancy way of saying beta test will remain open until March 5th and is available for PC - boo - and Android devices -... | Read more »
Prepare to get your mind melted as Evang...
If you are a fan of sci-fi shooters and incredibly weird, mind-bending anime series, then you are in for a treat, as Goddess of Victory: Nikke is gearing up for its second collaboration with Evangelion. We were also treated to an upcoming... | Read more »
Square Enix gives with one hand and slap...
We have something of a mixed bag coming over from Square Enix HQ today. Two of their mobile games are revelling in life with new events keeping them alive, whilst another has been thrown onto the ever-growing discard pile Square is building. I... | Read more »
Let the world burn as you have some fest...
It is time to leave the world burning once again as you take a much-needed break from that whole “hero” lark and enjoy some celebrations in Genshin Impact. Version 5.4, Moonlight Amidst Dreams, will see you in Inazuma to attend the Mikawa Flower... | Read more »
Full Moon Over the Abyssal Sea lands on...
Aether Gazer has announced its latest major update, and it is one of the loveliest event names I have ever heard. Full Moon Over the Abyssal Sea is an amazing name, and it comes loaded with two side stories, a new S-grade Modifier, and some fancy... | Read more »
Open your own eatery for all the forest...
Very important question; when you read the title Zoo Restaurant, do you also immediately think of running a restaurant in which you cook Zoo animals as the course? I will just assume yes. Anyway, come June 23rd we will all be able to start up our... | Read more »
Crystal of Atlan opens registration for...
Nuverse was prominently featured in the last month for all the wrong reasons with the USA TikTok debacle, but now it is putting all that behind it and preparing for the Crystal of Atlan beta test. Taking place between February 18th and March 5th,... | Read more »

Price Scanner via MacPrices.net

AT&T is offering a 65% discount on the ne...
AT&T is offering the new iPhone 16e for up to 65% off their monthly finance fee with 36-months of service. No trade-in is required. Discount is applied via monthly bill credits over the 36 month... Read more
Use this code to get a free iPhone 13 at Visi...
For a limited time, use code SWEETDEAL to get a free 128GB iPhone 13 Visible, Verizon’s low-cost wireless cell service, Visible. Deal is valid when you purchase the Visible+ annual plan. Free... Read more
M4 Mac minis on sale for $50-$80 off MSRP at...
B&H Photo has M4 Mac minis in stock and on sale right now for $50 to $80 off Apple’s MSRP, each including free 1-2 day shipping to most US addresses: – M4 Mac mini (16GB/256GB): $549, $50 off... Read more
Buy an iPhone 16 at Boost Mobile and get one...
Boost Mobile, an MVNO using AT&T and T-Mobile’s networks, is offering one year of free Unlimited service with the purchase of any iPhone 16. Purchase the iPhone at standard MSRP, and then choose... Read more
Get an iPhone 15 for only $299 at Boost Mobil...
Boost Mobile, an MVNO using AT&T and T-Mobile’s networks, is offering the 128GB iPhone 15 for $299.99 including service with their Unlimited Premium plan (50GB of premium data, $60/month), or $20... Read more
Unreal Mobile is offering $100 off any new iP...
Unreal Mobile, an MVNO using AT&T and T-Mobile’s networks, is offering a $100 discount on any new iPhone with service. This includes new iPhone 16 models as well as iPhone 15, 14, 13, and SE... Read more
Apple drops prices on clearance iPhone 14 mod...
With today’s introduction of the new iPhone 16e, Apple has discontinued the iPhone 14, 14 Pro, and SE. In response, Apple has dropped prices on unlocked, Certified Refurbished, iPhone 14 models to a... Read more
B&H has 16-inch M4 Max MacBook Pros on sa...
B&H Photo is offering a $360-$410 discount on new 16-inch MacBook Pros with M4 Max CPUs right now. B&H offers free 1-2 day shipping to most US addresses: – 16″ M4 Max MacBook Pro (36GB/1TB/... Read more
Amazon is offering a $100 discount on the M4...
Amazon has the M4 Pro Mac mini discounted $100 off MSRP right now. Shipping is free. Their price is the lowest currently available for this popular mini: – Mac mini M4 Pro (24GB/512GB): $1299, $100... Read more
B&H continues to offer $150-$220 discount...
B&H Photo has 14-inch M4 MacBook Pros on sale for $150-$220 off MSRP. B&H offers free 1-2 day shipping to most US addresses: – 14″ M4 MacBook Pro (16GB/512GB): $1449, $150 off MSRP – 14″ M4... Read more

Jobs Board

All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.