TweetFollow Us on Twitter

VBL Task Animation
Volume Number:5
Issue Number:2
Column Tag:C Workshop

Related Info: Vert. Retrace Mgr

VBL Task Animation

By Dick Chandler, Ben Lomond, CA

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

Dick Chandler is a Software Engineer at Apple Computer. His major interests are graphics and networks. This is his first article for MacTutor. In this article, Dick shows us how to do some cute animation of fingers drumming on the desktop!

What is a VBL task? A VBL or Vertical BLanking interrupt occurs when the beam of the display tube returns to the top of the screen. This happens on a regular interval (60 times a second). This is a convenient time to take care of recurrent system tasks such as: increment tickcount, check stack/heap boundries for collision, check and update cursor for movement, etc.

The information for executing each of these tasks is placed in a structure called appropriately enough a ‘VBLTask’ and is installed in the vertical retrace queue. Once this is done the system automatically executes the task at a regular interval.

You can place your own tasks on the queue for the system to execute. VBL tasks are a marvelous way of doing some types of graphic animation for the following reasons:

° You don’t have to worry about the speed of your animation on a faster/slower machine, the VBL will execute at the frequency of ticks you select (barring any unusually long tasks such as a disk inserted event hogging your time).

° You won’t get the flicker you see on the screen when trying to do moderately fast animation. This flicker occurs when the screen redraws itself half way through drawing your graphic.

° Plus once you’ve loaded a task on the queue, you needn’t worry about the task until you want to remove it.

Like almost everything else in programming, vbl tasks are easy once you’ve done one (after that its all copy and paste). This example program installs a vbl task which displays a number of icons sequentially. It could easily be modified to move the icons (or bitmaps) around the screen creating game graphics.

The main program is fairly straight forward. The only unusual thing you might find is the declaration of the ‘SetUpA5’ and ‘RestoreA5’ calls. If your task uses any global variables at all, you must insure that the A5 register contains the address of the boundary between the application globals and the application parameters. This is important since you can’t be sure from where the vbl task will be called.

The program basically opens a simple window, installs our vbl task, waits for a button click then exits after removing the task.

/*********************************************
 vblTask.c
*             an VBL task animation example
*
*       Written by Dick Chandler
*       
*This program is intentionally kept as 
*simple as possible, so that it could be 
*easily entered and/or understood.  
*Therefore there are no calls made to 
*check events nor any menus implemented.  ********************************************/

/*****  the only includes we’ll need  *****/
#include<types.h>
#include<quickdraw.h>
#include<windows.h>
#include<toolutils.h>
#include<events.h>
#include<Retrace.h>
#include<OSUtils.h>
#include<Strings.h>

/*****  define our own ‘A5’ routines  *****/
pascal void SetUpA5a() extern 0x2f0d;
pascal void SetUpA5b() extern 0x2a78;
pascal void SetUpA5c() extern 0x0904;

#define  SetUpA5() SetUpA5a(); SetUpA5b(), SetUpA5c()

/* just for readibility
#define NOT !

pascal void RestoreA5() extern 0x2a5f;

/*****  Globals  *****/
/* location of icons displayed */ 
Rect  iconRec = {30,30,62,62};
/* window rectangle */
Rect  boundsRect = {30,30,120,120};

/* tasks VBL record */ 
VBLTask StatusTask;
/* task routines */ 
void vblTask(), installTask(), removeTask();             
/* time between icons */
long    interval;

/*****  constants  *****/
#define FIRST_ICON 1000
#define LAST_ICON1005
#define MAX_NUMBER_ICONS  (LAST_ICON - FIRST_ICON) +1
#define SECONDS  60

/*********************************************
 the main program
********************************************/
int main()
{
WindowRecordeditWindowRecord;
WindowPtr editWindowPtr;

 InitGraf (&qd.thePort);  
 InitWindows();  
 /*
 * open a small, simple (and humble) 
 * window  
 */
 editWindowPtr = NewWindow(&editWindowRecord,&boundsRect, “”, true,
 1, (-1), false,  nil);
 SetPort( editWindowPtr );
 /*
 * set the interval time between icons  
 * and install our task on vbl queue   
 */
 interval = SECONDS/8;
 installTask( &StatusTask );
 /*
 * run until the button is clicked 
 */
 while  ( NOT Button() )  ;
 /*
 * clean up and exit
 */
 removeTask ( &StatusTask );
 CloseWindow(editWindowPtr);
 return 0;
}

The function ‘installTask’ sets up the required parameters for the vbl task. These parameters are passed via a ‘VBLTask’ record when the task is installed with the toolbox call ‘VInstall’.

° ‘vblAddr’ is the address of the function we’ve written and want the system to execute.

° ‘vblCount’ is the count, in ticks, to wait before calling the vblTask for the first time. We will reset this value everytime the task is executed if we want it to be reexecuted.

° ‘vblPhase’ allows you an additional offset before calling vblTask for the first time only. This would be useful if you wanted to install several graphic image tasks but did not want them to all look in sync.

° ‘qType’ designates the task a vbl task.

The function ‘removeTask’ simply removes the task from the queue with the toolbox call ‘VRemove’.

/************** NAME:installTask
*INPUT: a pointer to a VBL task record
*
*FUNCTION:installs our vblTask after 
*setting the vbl parameters 
********************************************/
void installTask( StatusTask )
VBLTask *StatusTaskPtr; 
{
 StatusTaskPtr->vblAddr   = vblTask;
 StatusTaskPtr->vblCount  = 10;
 StatusTaskPtr->vblPhase  = 0;
 StatusTaskPtr->qType     = vType;
 VInstall (StatusTaskPtr);
}

/************* NAME: removeTask
*INPUT: a pointer to a VBL task record
*
*FUNCTION:removes our vbl task
*******************************************/
void removeTask ( StatusTask )
VBLTask *StatusTaskPtr;
{
 VRemove(StatusTask);
}

‘vblTask’ is our routine which we loaded into the vbl record and installed. The routine sets up and later restores the A5 register so we can use our own global varibles. It is important to note that you cannot make any calls to the memory manager, and you cannot rely on locked handles being valid. These caveats are outlined in the ‘Vertical Retrace Manager’, Inside Macintosh V 1-3.

‘vblTask’ decides which of our icons to display next and then displays it if it finds the icon. Notice that we must reset the ‘vblCount’ each time or the task will not be called again.

/*******************
 NAME:vblTask    
*
*FUNCTIONS: our actual vbl task which gets 
*called every ‘interval’ ticks
********************************************/
void vblTask()
{
static long icons; 
Handle  tempIcon;
static long timeIcon = FIRST_ICON; 

 SetUpA5(); /* set up A5 register */
 icons = MAX_NUMBER_ICONS;
 StatusTask.vblCount = interval; timeIcon++; /*bumpicon */
 if( timeIcon > LAST_ICON ) 
 timeIcon = FIRST_ICON;
 tempIcon = GetIcon( timeIcon )
 if( tempIcon )
 PlotIcon( &iconRec, tempIcon );
 RestoreA5();  /* preserve A5 register */
}

The only resources you will need are icons to display. I attached six ‘drumming fingers’ icons [included in the source code disk.-Ed] I used in the program thanks to graphic artists Irene Welch and Shelley van Bronkhorst. However, you can attach any number of icons you wish as long as you change the defined constants ‘FIRST_ICON’ and ‘LAST_ICON’.

The program can be compiled and linked with the following commands. You can either paste in the resources with ResEdit, or derez and rez the resources into the application.

derez vblTaskResources Types.r SysTypes.r > vblTask.r
Rez Types.r SysTypes.r vblTask.r -o vblTask -a

SetFile -a B vblTask -c MOBY -t APPL

C -g vblTask.c
Link  vblTask.c.o 
 “HD:MPW:CLibraries:”CRuntime.o 
 “HD:MPW:CLibraries:”CInterface.o 
 -o vblTask

VBL Animation Problems

David Oster

Berkeley, CA

I am appalled by Dick Chandler’s article, “VBL Task Animation” in the February 1989 issue of MacTutor. Yes, his program works, but only because it is a top. Any real program that tries the technique he describes will fail miserably.

Look, his VBL task calls GetIcon and PlotIcon at VBL interrupt time. In his application, the main loop just busy waits for the user to press the Button. A real application would be calling GetNextEvent(), or doing something. For example, each time the user looks at a menu. When the menu goes away, it slams those bits back and deallocates the handle.

GetIcon calls GetResource(). What if the VBL task calls it while the Memory Manager is shuffling the heap to allocate memory for the main loop. Crash city. PlotIcon calls CopyBits(), which clips against the clipRgn and visRgn of the underlying grafPort. What if the VBL task calls it while the Memory Manager is shuffling the heap to allocate memory for the main loop? Crash city.

Even if your program is clean, you do not know what trap patches the user has installed: Maybe he is using an INIT that overrides some trap your program needs, and the override will do memory allocation. For example, Dick’s program calls Button() from its main loop, and many INITs override button, so they will get called while the mouse is down.

So, you can only do animation at interrupt time if you can guarantee that no user or system task will allocate memory in the main loop.

Dick’s program doesn’t guarantee this, since it calls Button() from its main loop, and Button() may have been overriden by an INIT. Since there is so little the main loop can safely do, you might as well give up on VBL Task animation, and just do animation in your main loop, busy waiting until TickCount changes to pause between animation frames.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Opera 44.0.2510.1449 - High-performance...
Opera is a fast and secure browser trusted by millions of users. With the intuitive interface, Speed Dial and visual bookmarks for organizing favorite sites, news feature with fresh, relevant content... Read more
Skim 1.4.29 - PDF reader and note-taker...
Skim is a PDF reader and note-taker for OS X. It is designed to help you read and annotate scientific papers in PDF, but is also great for viewing any PDF file. Skim includes many features and has a... Read more
FontExplorer X Pro 6.0.2 - Font manageme...
FontExplorer X Pro is optimized for professional use; it's the solution that gives you the power you need to manage all your fonts. Now you can more easily manage, activate and organize your... Read more
1Password 6.7.1 - Powerful password mana...
1Password is a password manager that uniquely brings you both security and convenience. It is the only program that provides anti-phishing protection and goes beyond password management by adding Web... Read more
Vivaldi 1.9.818.44 - An advanced browser...
Vivaldi is a browser for our friends. In 1994, two programmers started working on a web browser. Our idea was to make a really fast browser, capable of running on limited hardware, keeping in mind... Read more
Vivaldi 1.9.818.44 - An advanced browser...
Vivaldi is a browser for our friends. In 1994, two programmers started working on a web browser. Our idea was to make a really fast browser, capable of running on limited hardware, keeping in mind... Read more
Skim 1.4.29 - PDF reader and note-taker...
Skim is a PDF reader and note-taker for OS X. It is designed to help you read and annotate scientific papers in PDF, but is also great for viewing any PDF file. Skim includes many features and has a... Read more
1Password 6.7.1 - Powerful password mana...
1Password is a password manager that uniquely brings you both security and convenience. It is the only program that provides anti-phishing protection and goes beyond password management by adding Web... Read more
FontExplorer X Pro 6.0.2 - Font manageme...
FontExplorer X Pro is optimized for professional use; it's the solution that gives you the power you need to manage all your fonts. Now you can more easily manage, activate and organize your... Read more
VOX 2.8.24 - Music player that supports...
VOX just sounds better! The beauty is in its simplicity, yet behind the minimal exterior lies a powerful music player with a ton of features and support for all audio formats you should ever need.... Read more

Latest Forum Discussions

See All

Fire Emblem Heroes event announces new m...
As reported yesterday, Nintendo was gearing up a live press event for their popular mobile game,Fire Emblem Heroes. While the stream revealed a lot of new things, the event was entirely in Japanese. Luckily we have a rundown of what was announced... | Read more »
Best games we played this week
Another week, another slate of new mobile games. Although there weren't as many big name releases as last week, there were plenty of unique video game titles that came out that's sure to keep you interested over the weekend. Everything from classic... | Read more »
Olli by Tinrocket (Photography)
Olli by Tinrocket 1.0 Device: iOS iPhone Category: Photography Price: $2.99, Version: 1.0 (iTunes) Description: Get drawn in with Olli by TinrocketOlli instantly turns your everyday moments into hand-drawn art and animations. • Watch... | Read more »
Penarium (Games)
Penarium 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: | Read more »
Fire Emblem Heroes is way more profitabl...
Profits for Nintendo's mobile game Fire Emblem Heroes are apparently impressive enough to beat out other Nintendo titles likeSuper Mario Run, despite having 10 times fewer downloads. [Read more] | Read more »
Classic series Robot Unicorn Attack 3 no...
The classic Adult Swim browser game, Robot Unicorn Attack, branched off into a series of popular mobile games. Now, the latest entry into the series, Robot Unicorn Attack 3, is available for iOS and Android mobile devices. [Read more] | Read more »
Sudoku Sweeper (Games)
Sudoku Sweeper 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: A minimalist mashup of Minesweeper and Sudoku. Logic puzzle perfection. Every row, column and zone contains a bomb and one of... | Read more »
Under Leaves (Games)
Under Leaves 1.0.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0.0 (iTunes) Description: Journey into the forest, the jungle or the depths of the deep blue sea. Find chestnuts for the pigs, a caterpillar for the... | Read more »
Ninja Pizza Girl (Games)
Ninja Pizza Girl 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: In the not-so-distant future, rampart traffic congestion has resulted in only one way to deliver pizzas across town in thirty... | Read more »
SCRAP (Games)
SCRAP 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: That day, for no apparent reason, SCRAP decided to wake up and run. He had to, because his activation was a mistake the "Factory" could... | Read more »

Price Scanner via MacPrices.net

15-inch 2.7GHz Space Gray Touch Bar MacBook P...
B&H Photo has the 15″ 2.7GHz Space Gray Touch Bar MacBook Pro in stock today and on sale for $2599…$200 off MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: - 15″ 2.7GHz... Read more
13-inch 2.9GHz/256GB Space Gray Touch Bar Mac...
B&H Photo has the 13″ 2.9GHz/256GB Space Gray Touch Bar MacBook Pro in stock today and on sale for $150 off MSRP including free shipping plus NY & NJ sales tax only: - 13″ 2.9GHz/256GB Touch... Read more
21-inch iMacs on sale for up to $151 off MSRP
B&H Photo has 21″ iMacs on sale for up to $151 off MSRP, each including free shipping plus NY sales tax only: - 21″ 3.1GHz iMac 4K: $1348 $151 off MSRP - 21″ 2.8GHz iMac: $1199.99 $100 off MSRP... Read more
Weekend deal: Up to $420 off new MacBook Pros...
Apple has Certified Refurbished 2016 15″ and 13″ MacBook Pros available for $230 to $420 off original MSRP. An Apple one-year warranty is included with each model, and shipping is free: - 15″ 2.6GHz... Read more
Price drop: 15-inch 2.2GHz Retina MacBook Pro...
Amazon has dropped their price on 15″ 2.2GHz Retina MacBook Pros (MJLQ2LL/A) to $1709.99 including free shipping. Their price is $290 off MSRP for this model. Note that stock may sell out quickly at... Read more
2.8GHz Mac mini on sale for $899, save $100
B&H Photo has the 2.8GHz Mac mini (model number MGEQ2LL/A) on sale for $899 including free shipping plus NY & NJ sales tax only. Their price is $100 off MSRP. Read more
Check Apple prices on any device with the iTr...
MacPrices is proud to offer readers a free iOS app (iPhones, iPads, & iPod touch) and Android app (Google Play and Amazon App Store) called iTracx, which allows you to glance at today’s lowest... Read more
New System Clock for macOS by B-Eng Now Avail...
Fehraltorf, Switzerland based B-Eng has announced the release and immediate availability of System Clock, the company’s new system monitor and information app developed exclusively for macOS. System... Read more
DEVONtechnologies Celebrates 15th Anniversary...
DEVONtechnologies celebrates its 15th company anniversary with a 30% discount on all its software products from May 1st through 5th, 2017. In spring 2002, DEVONtechnologies opened its website and... Read more
WaterField Designs Invites Customers to Help...
San Francisco based WaterField Designs invites customers and air travelers to participate in developing the next generation in-flight travel case, the Air Porter. Frustrated with limited legroom,... Read more

Jobs Board

Best Buy *Apple* Computing Master - Best Bu...
**501846BR** **Job Title:** Best Buy Apple Computing Master **Location Number:** 001126-South Bay Center-Store **Job Description:** **What does a Best Buy Apple Read more
Consultant or Sr. Consultant, *Apple* Allia...
…improve our business and your clients will be heard.Project Manager, Apple AllianceLocation:San Francisco preferred, open to other locationsLevel:Consultant or Sr. Read more
*Apple* Mac Computer Technician - GeekHampto...
…complex computer issues over the phone and in person? GeekHampton, Long Island's Apple Premium Service Provider, is looking for you! Come work with our crew Read more
*Apple* Mobile Master - Best Buy (United Sta...
**501505BR** **Job Title:** Apple Mobile Master **Location Number:** 000849-Gurnee-Store **Job Description:** **What does a Best Buy Apple Mobile Master do?** At Read more
Best Buy *Apple* Computing Master - Best Bu...
**498428BR** **Job Title:** Best Buy Apple Computing Master **Location Number:** 000293-Rockville-Store **Job Description:** **What does a Best Buy Apple Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.