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

SpamSieve 2.9.38 - Robust spam filter fo...
SpamSieve is a robust spam filter for major email clients that uses powerful Bayesian spam filtering. SpamSieve understands what your spam looks like in order to block it all, but also learns what... Read more
TeamViewer 15.0.8397 - Establish remote...
TeamViewer gives you remote control of any computer or Mac over the Internet within seconds or can be used for online meetings. Find out why more than 200 million users trust TeamViewer! Free for non... Read more
SteerMouse 5.4.3 - Powerful third-party...
SteerMouse is an advanced driver for USB and Bluetooth mice. SteerMouse can assign various functions to buttons that Apple's software does not allow, including double-clicks, modifier clicks,... Read more
Toast Titanium 18.2.1 - The ultimate med...
Roxio Toast Titanium, the leading DVD burner for Mac, makes burning even better, adding Roxio Secure Burn to protect your files on disc and USB in Mac- or Windows-compatible formats. Get more style... Read more
HoudahSpot 5.0.11 - Advanced file-search...
HoudahSpot is a versatile desktop search tool. Use HoudahSpot to locate hard-to-find files and keep frequently used files within reach. HoudahSpot will immediately feel familiar. It works just the... Read more
ClipGrab 3.8.6 - Download videos from Yo...
ClipGrab is a free downloader and converter for YouTube, Vimeo, Facebook and many other online video sites. It converts downloaded videos to MPEG4, MP3 or other formats in just one easy step Version... Read more
ExpanDrive 7.4.0 - Access cloud storage...
ExpanDrive builds cloud storage in every application, acts just like a USB drive plugged into your Mac. With ExpanDrive, you can securely access any remote file server directly from the Finder or... Read more
Adobe Dreamweaver CC 2020 20.0 - Build w...
Dreamweaver CC 2020 is available as part of Adobe Creative Cloud for as little as $20.99/month (or $9.99/month if you're a previous Dreamweaver customer). Adobe Dreamweaver CC 2020 allows you to... Read more
Eye Candy 7.2.3.85 - 30 professional Pho...
Eye Candy renders realistic effects that are difficult or impossible to achieve in Photoshop alone, such as Fire, Chrome, and the new Lightning. Effects like Animal Fur, Smoke, and Reptile Skin are... Read more
Sparkle Pro 2.8.5 - Visual website creat...
Sparkle Pro will change your mind if you thought building websites wasn't for you. Sparkle is the intuitive site builder that lets you create sites for your online portfolio, team or band pages, or... Read more

Latest Forum Discussions

See All

Pre-register for Hello Kitty AR: Kawaii...
Hello Kitty — the cute cat that launched a multi-billion-pound franchise — has been brought to life… sort of. Sanrio has teamed up with the Bublar Group to create a new mobile game that uses AR tech to turn the real world into Hello Kitty’s... | Read more »
Gorgeous and tranquil puzzler Spring Fal...
One-man indie studio SPARSE//GameDev has now launched its tranquil puzzler, Spring Falls. It's described as "a peaceful puzzle game about water, erosion, and watching things grow". [Read more] | Read more »
Black Desert Mobile gets an official rel...
Pearl Abyss has just announced that its highly-anticipated MMO, Black Desert Mobile, will launch globally for iOS and Android on December 11th. [Read more] | Read more »
Another Eden receives new a episode, cha...
Another Eden, WFS' popular RPG, has received another update that brings new story content to the game alongside a few new heroes to discover. [Read more] | Read more »
Overdox guide - Tips and tricks for begi...
Overdox is a clever battle royale that changes things up by adding MOBA mechanics and melee combat to the mix. This new hybrid game can be quite a bit to take in at first, so we’ve put together a list of tips to help you get a leg up on the... | Read more »
Roterra Extreme - Great Escape is a pers...
Roterra Extreme – Great Escape has been described by developers Dig-It Games as a mini-sequel to their acclaimed title Roterra: Flip the Fairytale. It continues that game's tradition of messing with which way is up, tasking you with solving... | Read more »
Hearthstone: Battlegrounds open beta lau...
Remember earlier this year when auto battlers were the latest hotness? We had Auto Chess, DOTA Underlords, Chess Rush, and more all gunning for our attention. They all had their own reasons to play, but, at least from where I'm standing, most... | Read more »
The House of Da Vinci 2 gets a new gamep...
The House of Da Vinci launched all the way back in 2017. Now, developer Blue Brain Games is gearing up to deliver a second dose of The Room-inspired puzzling. Some fresh details have now emerged, alongside the game's first official trailer. [Read... | Read more »
Shoot 'em up action awaits in Battl...
BattleBrew Productions has just introduced another entry into its award winning, barrelpunk inspired, BattleSky Brigade series. Whilst its previous title BattleSky Brigade TapTap provided fans with idle town building gameplay, this time the... | Read more »
Arcade classic R-Type Dimensions EX blas...
If you're a long time fan of shmups and have been looking for something to play lately, Tozai Games may have just released an ideal game for you on iOS. R-Type Dimensions EX brings the first R-Type and its sequel to iOS devices. [Read more] | Read more »

Price Scanner via MacPrices.net

13″ 2.4GHz MacBook Pros available for up to $...
Apple has a full line of Certified Refurbished 2019 13″ 2.4GHz 4-Core Touch Bar MacBook Pros available starting at $1529 and up to $300 off MSRP. Apple’s one-year warranty is included, shipping is... Read more
New at T-Mobile: Switch to T-Mobile, and get...
T-Mobile is offering a free 64GB iPhone 8 for new customers who switch to T-Mobile and open a new line of service. Eligible trade-in required, and discount applied over a 24 month period. The fine... Read more
Xfinity Mobile’s Black Friday Apple savings:...
Take $250 off the purchase of any iPhone at Xfinity Mobile with a new line activation, and transfer of phone number to Xfinity Mobile, through December 8, 2019. This includes Apple’s new iPhone 11... Read more
2019 13″ 1.4GHz MacBook Pros available starti...
Apple has a full line of Certified Refurbished 2019 13″ 1.4GHz 4-Core Touch Bar MacBook Pros available starting at $1099 and up to $230 off MSRP. Apple’s one-year warranty is included, shipping is... Read more
Save up to $350 on a 21″ or 27″ iMac with the...
Apple has Certified Refurbished 2019 21″ & 27″ iMacs available starting at $929 and up to $350 off the cost of new models. Apple’s one-year warranty is standard, shipping is free, and each iMac... Read more
Early Holiday 2019 Sale: B&H again offers...
B&H Photo has 10.2″ iPads on sale again for $30 off Apple’s MSRP, starting at $299, as part of their early Holiday 2019 sale. Overnight shipping is free to many addresses in the US: – 10.2″ 32GB... Read more
Apple iMacs on sale today at B&H Photo fo...
B&H Photo has new 2019 21″ and 27″ 5K iMacs on stock today and on sale for up to $150 off Apple’s MSRP. Overnight shipping is free to many locations in the US. These are the same iMacs sold by... Read more
2018 4 and 6-Core Mac minis on sale today for...
Apple resellers are offering new 2018 4-Core and 6-Core Mac minis for $80-$100 off MSRP for a limited time. B&H Photo has the new 2018 4-Core and 6-Core Mac minis on sale for up to $100 off Apple... Read more
Early Holiday 2019 sale at B&H Photo: 12....
B&H Photo has new 12.9″ iPad Pros on sale for up to $120 off Apple’s MSRP as part of their early Holiday 2019 sale. Overnight shipping is free to many addresses in the US: – 12.9″ 64GB WiFi iPad... Read more
8-Core iMac Pro on sale today for $4499 at B...
B&H Photo has the base 8-Core 3.2GHz 32GB/1TB iMac Pro on sale today for $4499 — $500 off Apple’s MSRP. Shipping is free. Their price is the lowest available for a new iMac Pro from any Apple... Read more

Jobs Board

*Apple* Health Benefit Specialist - Call Cen...
Description ** Apple Health Benefit Specialist - Call Center (MAS 3/MACSC)** **Olympia, WA Multiple Positions** *The ideal candidate for this position will have Read more
Hair Stylist - *Apple* Blossom Mall - JCPen...
Hair Stylist - Apple Blossom Mall Location:Winchester, VA, United States- Apple Blossom Mall 1850 Apple Blossom Dr Job ID:1065040Salon Professionals Job Read more
*Apple* Mobility Pro - Best Buy (United Stat...
**747088BR** **Job Title:** Apple Mobility Pro **Job Category:** Store Associates **Store NUmber or Department:** 000297-Reston-Store **Job Description:** At Best Read more
Nurse Practitioner - Field Based (San Bernard...
Nurse Practitioner - Field Based (San Bernardino, CA, Apple Valley, Hesperia) **Location:** **United States** **Requisition #:** PS30312 **Post Date:** Nov 11, 2019 Read more
Best Buy *Apple* Computing Master - Best Bu...
**747061BR** **Job Title:** Best Buy Apple Computing Master **Job Category:** Store Associates **Store NUmber or Department:** 000647-Kildeer-Store **Job Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.