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Related Info: Vert. Retrace Mgr Event Manager Color Quickdraw

Color Animation

By Ajay Nath, Oakland Gardens, NY

It all started when I started playing with a shareware breakout game. Paul, a friend of mine who saw me playing it, thought it was neat and liked playing it but there were a few problems with the game. It was an old game and didn’t use the larger screen of my Mac IIcx or color and it had other annoying things about it. Well I’ve been much too busy to write a new game for my friend, but I was able to discover a method for doing simple animation that will work well on a Mac II or better machine.

When I first sat down and thought about the problem I thought, well I’ll simply use a vbl task to set a global variable and my program’s main loop will examine that variable and know when to draw. To do this I declared a variable of the following simple type:

{1}

 XVBLRec= RECORD
 xVBLTask : VBLTask;
 xDoTask: INTEGER;
 END;

The first field of the record (xVBLTask) is used in the calls to install and remove the vbl task, the second field xDoTask is an integer which the vbl task I use will set to 1 when it runs. My programs main loop just has to examine the xDoTask field and draw when it is non-zero.

This technique is not very different from the method which involves examining the current value of the Mac global variable TickCount and drawing when it changes, i.e. (in pseudocode):

{2}

 count = TickCount;
 while count = TickCount do nothing;
 { start drawing real fast! }.

On older Macs the TickCount was changed when vbl tasks were run so the above method was really very similar to using a vbl task to set a global variable.

I took a quick look in Inside Mac Vol. V (pp. 566-567) before I started writing my vbl task and found some interesting information there. The new Macs have vertical retrace interrupts which can vary according to their video card and we can create vbl tasks which run at the ‘heart rate’ of the whichever video card we want. Well, the obvious thing to do is to run our vbl task at the rate of the video card of our main screen, and we then should be able to do simple animation easily! The new calls are called SlotVInstall and SlotVRemove and just like the old calls need a pointer to a vbltask record but in addition, need a slot number so they know which slot to attach the vbl task to. All we need to know then is the slot number of the video card which drives our main screen. After a quick five minute search through IM V I found a call, “GetVideoDefault”, which would give me the slot number of the default video card and I was on my way.

I used TML Pascal II to write my main program and used MPW Assembler to write the vbl task. I’ll explain the vbl tasks code first since its so simple (only three lines). When the task runs, register A0 is a ptr to our vbltask record and this allows us to reset our tasks vblcount. Since we defined an integer that comes right after this record in our XVBLRec type (see above), we can change its value to 1 at this point since A0 points to our record. The three lines of the vbl task do the following (in pseudocode):

1) reset the vblcount

2) set the xDoTask variable to 1

3) return (exit) from the vbl task.

All the main program loop has to do is (in pseudocode):

 repeat
 if (xDoTask <> 0) begin
 DrawStuff;
 set xDoTask to 0
 endif
 until done

The following MPW commands will build and run the example program (you may need to change the paths to build it on your hard disk):

# 3

####
Asm vbltask.a
TMLPascal slotvbltaskdemo.p
Link -w -t ‘APPL’ -c ‘????’ 
 slotvbltaskdemo.p.o vbltask.a.o 
 “HD-80:MPW:Libraries:Libraries:”Runtime.o 
 “HD-80:MPW:Libraries:Libraries:”Interface.o 
 “HD-80:MPW:Libraries:TMLPLibraries:”TMLPasLib.o 
 “HD-80:MPW:Libraries:TMLPLibraries:”SANELib.o 
 -o SlotVBLTaskDemo
Rez -append -o SlotVBLTaskDemo slotvbltaskdemo.r
SlotVBLTaskDemo
####

Note that the code does check to make sure that the machine its running on is a Mac II or better before running, since the new calls are not available on lower end machines. On lower machines using regular vbl tasks is probably sufficient to do simple animation. That’s about all the explanation the code needs other than to say that it ‘bounces’ a red string vertically in its draggable window and can run in the background.

There is a bug which occurs when things are being drawn at the top of the screen and when you use the simple method of ‘erase old stuff then draw new stuff’ as I do in this example. You may see things start to flicker when drawing at the top of the screen. The problem I think is in the way the screen is drawn which is left to right and from top to bottom. I haven’t thought of a solution for this problem yet other than to use a call to CopyBits to blast in whatever your drawing, rather then to use straight QuickDraw calls. If anyone can think of a good explanation of this problem and how to solve it I’d like to hear about it.

Much love and thanks to the boys of ‘9A’ and of course, to K.S.

Listing:  vbltask.a

 INCLUDE‘SysEqu.a’
 EXPORT MyVBLTask

MyVBLTask PROC
;
; On entry A0 is a ptr to our XVBLRec which was defined
; as follows:
;
;XVBLRec= RECORD
;xVBLTask : VBLTask;
;xDoTask: INTEGER;
;END;
;
; We can use MPW RECORDs to define it in assembly as follows:
;
XVBLRec RECORD 0
xVBLTaskDS.BvblPhase+2
xDoTask DS.W1
 ENDR

kVBLCount EQU    1

 WITH XVBLRec
 ; Reset the vblCount
 MOVE.W #kVBLCount,XVBLRec+xVBLTask+vblCount(A0)

 ; Make xDoTask non-zero
 MOVE.W #1,XVBLRec+xDoTask(A0)

 ; Exit Task
 RTS

ENDWITH
ENDP
 END  ; For Assembler

Listing:  slotvbltaskdemo.p

PROGRAM SlotVBLTaskDemo;

USES
 MemTypes, QuickDraw, OSIntf, ToolIntf;

{ Declare our external vbl task }
PROCEDURE MyVBLTask; EXTERNAL;

CONST
 F =  False;
 T =  True;
 kBallSpeed =  4;

TYPE
 XVBLRec= RECORD
 xVBLTask : VBLTask;
 xDoTask: INTEGER;
 END;

VAR
 gDone  : BOOLEAN;
 gVideoInfoRec : DefVideoRec;
 gEvt : EventRecord;
 gFontInfo: FontInfo;
 gBoxDir: INTEGER;
 gBoxRect : Rect;
 gBoxColor: RGBColor;
 gBoxString :  Str255;

 gDragRect,
 gRect  : Rect;
 gMainWindow:  WindowPtr;
 gWRec  : WindowRecord;

 gXVBLRec : XVBLRec;

{ Proc to run if a crash occurs }
PROCEDURE Crash;
BEGIN
 ExitToShell;
END;

{ Proc that does MacInits }
PROCEDURE MacInits;
BEGIN
 MaxApplZone;

 MoreMasters;
 MoreMasters;
 MoreMasters;
 MoreMasters;

 InitGraf (@thePort);
 InitFonts;
 InitWindows;
 InitMenus;
 TEInit;
 InitDialogs (@Crash);
 InitCursor;
END;

{ Proc that sets up our window }
PROCEDURE SetUpWindows;
BEGIN
 gRect := ScreenBits.bounds;
 WITH gRect DO BEGIN
 left := left + 20;
 right := left + 400;
 top := top + 40;
 bottom := bottom - 20;
 END;

 gMainWindow := NewCWindow (@gWRec, gRect,
 ‘SlotVBLTaskDemo - Click in this window to Exit’,
 T, noGrowDocProc, WindowPtr (-1), F, 0);
 SetPort (gMainWindow);
END;

{ Proc that sets up the box for our ball }
PROCEDURE SetUpBox;
VAR
 width  : INTEGER;
BEGIN
 gBoxDir := kBallSpeed;

 gBoxString := ‘I love you Manu’;

 width := StringWidth (gBoxString);

 GetFontInfo (gFontInfo);

 WITH gBoxRect DO BEGIN
 top := 10;
 bottom := top + gFontInfo.ascent + gFontInfo.descent;
 left := ((gRect.right - gRect.left) DIV 2) - (width DIV 2);
 right := left + width;
 END;

 WITH gBoxColor DO BEGIN
 red := -1;
 green := 0;
 blue := 0;
 END;

 RGBForeColor (gBoxColor);
END;

{ Proc that inits our globals }
PROCEDURE GlobalInits;
BEGIN
 SetUpWindows;
 SetUpBox;
 gDragRect := ScreenBits.bounds;
 InsetRect (gDragRect, 4, 4);

 gDone := F;
END;

{ Proc that cleans up before we exit }
PROCEDURE CleanUps;
BEGIN
 CloseWindow (gMainWindow);
END;

{ Func that makes sure we run in the currect environment }
FUNCTION EnvironmentOK : BOOLEAN;
VAR
 err  : OSErr;
 theWorld : SysEnvRec;
BEGIN
 EnvironmentOK := F; { Assume env is bad }

 err := SysEnvirons (curSysEnvVers, theWorld);

 IF (err = noErr) THEN BEGIN
 IF (theWorld.machineType >= envMacII) THEN
 EnvironmentOK := T;
 END; { IF }
END;

{ Func that sets up our vbl task }
FUNCTION VBLTaskSetUp : BOOLEAN;
VAR
 err  : OSErr;
BEGIN
 VBLTaskSetUp := F; { Assume we fail }

 GetVideoDefault (@gVideoInfoRec);

 WITH gXVBLRec DO BEGIN
 xDoTask := 0;

 WITH xVBLTask DO BEGIN
 qType := ORD (vType);
 vblAddr := @MyVBLTask;
 vblCount := 1;
 vblPhase := 0;
 END;

 err := SlotVInstall (@xVBLTask, gVideoInfoRec.sdSlot);
 IF (err = noErr) THEN
 VBLTaskSetUp := T; { We succeeded! }
 END;
END;

{ Proc that removes our vbl task }
PROCEDURE RemoveVBLTask;
VAR
 err  : OSErr;
BEGIN
 err := SlotVRemove (@gXVBLRec.xVBLTask, gVideoInfoRec.sdSlot);
END;

{ Proc that draws our window }
PROCEDURE DrawStuff;
VAR
 oldPort: GrafPtr;
BEGIN
 GetPort (oldPort);
 SetPort (gMainWindow);
 EraseRect (gBoxRect);

 WITH gBoxRect DO BEGIN
 top := top + gBoxDir;
 bottom := bottom + gBoxDir;
 END;

 IF (gBoxRect.bottom >= gWRec.port.portRect.bottom) THEN
 gBoxDir := -kBallSpeed
 ELSE BEGIN
 IF (gBoxRect.top <= gWRec.port.portRect.top) THEN
 gBoxDir := kBallSpeed;
 END;

 MoveTo (gBoxRect.left, gBoxRect.bottom - gFontInfo.descent);
 DrawString (gBoxString);

 SetPort (oldPort);
END;

{ Proc that handles mouse downs }
PROCEDURE DoMouseDown;
VAR
 result : INTEGER;
 whichWindow:  WindowPtr;
BEGIN
 result := FindWindow (gEvt.where, whichWindow);

 CASE result OF
 inContent:
 gDone := T;
 inDrag:
 DragWindow (whichWindow, gEvt.where, gDragRect);
 OTHERWISE
 END;
END;

{ Main }
BEGIN
 MacInits;

 IF (EnvironmentOK) THEN BEGIN
 GlobalInits;

 IF (VBLTaskSetUp) THEN BEGIN

 REPEAT
 IF NOT (WaitNextEvent (mDownMask, gEvt, 0, NIL)) THEN BEGIN
 IF (gXVBLRec.xDoTask <> 0) THEN BEGIN
 DrawStuff;
 gXVBLRec.xDoTask := 0;
 END;
 END
 ELSE
 DoMouseDown;
 UNTIL (gDone);
 RemoveVBLTask;
 END;
 CleanUps;
 END;

 ExitToShell; { Back to the Finder! (or MultiFinder) }
END.

Listing:  slotvbltaskdemo.r

#include “Types.r”
#define kMinSize 25/* application’s minimum size (in K) */
#define kPrefSize50/* application’s preferred size (in K) */

resource ‘SIZE’ (-1) {
 dontSaveScreen,
 acceptSuspendResumeEvents,
 enableOptionSwitch,
 canBackground,  /* we can background  */
 multiFinderAware,
 backgroundAndForeground,
 dontGetFrontClicks,
 ignoreChildDiedEvents,
 not32BitCompatible,
 reserved,
 reserved,
 reserved,
 reserved,
 reserved,
 reserved,
 reserved,
 kPrefSize * 1024,
 kMinSize * 1024 
};