TweetFollow Us on Twitter

Cursor Control 2
Volume Number:6
Issue Number:9
Column Tag:C Workshop

Related Info: Quickdraw

Cursor Control

By Robert S. T. Gibson, Ontario, Canada

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

[Robert S. T. Gibson is a Senior Software Engineer at Atryx Software Design in Canada]

Although it is not suggested by anyone who follows the Macintosh user interface, it is occasionally necessary for a program to change or restrict the cursor position. Some programs move the cursor to lock it into a grid, some restrict the cursor to a specific region, and others (usually games) allow it to wrap around the screen. Games sometimes read the cursor position, compare it to the middle of the screen, and then move the cursor to the screen’s center to keep it from reaching the edge.

Cursor tracking is maintained by many system globals. The three we are interested in, however, are MTemp, RawMouse, Mouse, and CrsrNew (see Figure 1).

It is often dangerous to change the System’s low-memory globals if you don’t know their exact effects on your system.

As always, there is a right way and a wrong way to do this. I’ll skip the wrong way and get right to what I believe to be the correct way. The C techniques used here can easily be adapted into other programming languages.

It is a relatively simple task to set the mouse position, but it requires a bit of insight into how the System keeps control.

Figure 1. Mouse Globals

System Control

Operation of the mouse depends on two routines that are called during interrupts. The first routine simply sets the global variable CrsrNew to true if the mouse position has changed. The second routine is a vertical retrace (VBL) task, which checks the value of CrsrNew and draws the cursor in the new position if the value is true.

Providing CrsrNew is set, each time the VBL task is executed, it draws the cursor and copies the value of MTemp, the new location of the mouse, into the variable RawMouse, the saved (old) location. This allows the next execution to examine the two variables. If MTemp is a valid position, RawMouse is set to the new position and the cycle continues. The mouse location is copied in to the global variable Mouse for use by routines such as GetMouse().

Program Control

Only a few simple steps are required to set the mouse position properly and safely:

Step:

1: set MTemp to the new position

2: set RawMouse to new position

3: set CrsrNew to true

First, we should define our variables:

int             *MTemp;
char            *CrsrNew;

MTemp   = (int *)  0x828;
CrsrNew = (char *) 0x8CE;

Notice that MTemp was declared as an integer, and RawMouse and Mouse were not declared at all. Since the three points are in a row, it is much easier to simply declare the first variable as an integer and increment the pointer to each position to be set. NewPos is passed to our routine, containing the point to which the mouse should be moved in the following code excerpt. Remember that points are stored internally as (v,h) or (row,column), instead of (h,v).

!c

odeexamplestart/* 1 */

for (i=0;i<3;i++) {
 *(MTemp+2*i) = newPos.v;
 *(MTemp+2*i+1) = newPos.h;
}


Once the three points are set, the only task which remains to be done is the setting of the CrsrNew variable. To tell the System that the mouse has moved, the boolean must be set with a non-zero (true) value. Since it is set to -1 by the System, it will be so set here. Any true value should work, however.

/* 2 */

*CrsrNew = -1;

The System routine will realize that the global CrsrNew has been changed, will find the new position in MTemp and RawMouse and will draw the cursor in the new position.

Curse Control

It’s unwise to have your program confuse the user by moving the cursor too dramatically from where he would expect it to appear. If you are in a programming situation which is leading you to move the cursor to where you want it, rather than where the user expects it, you should think twice -- and then think again.

Listing:  Control.c

/*******
 * HandleMouse()
 * Checks the cursor position and calls MousePos if necessary
 *******/
HandleMouse(boundsRect)
Rect  *boundsRect;
{
Point   mousePoint;
Point   newPoint;

 GetMouse(&mousePoint);
 LocalToGlobal(&mousePoint);
 newPoint.h = newPoint.v = -1;
 
 if (mousePoint.h <= boundsRect->left)
 newPoint.h = boundsRect->right - 2;
 else
 if (mousePoint.h >= boundsRect->right - 1)
 newPoint.h = boundsRect->left + 1;
 if (mousePoint.v <= boundsRect->top)
 newPoint.v = boundsRect->bottom - 2;
 else
 if (mousePoint.v >= boundsRect->bottom - 1)
 newPoint.v = boundsRect->top + 1;
 
 if ( (newPoint.h + 1) || (newPoint.v + 1) )
 {
 newPoint.h = (newPoint.h != -1) ? newPoint.h : mousePoint.h;
 newPoint.v = (newPoint.v != -1) ? newPoint.v : mousePoint.v;
 MousePos(newPoint);
 }
}
Listing:  ControlMain.C

/* CursorControl */ /* by Rob Gibson */ /* August 22, 1989. */
/* MacHeaders Included */
/*********  Project file: Control.c  ControlMain.c             Functions.c 
 MacTraps MousePos.c
 Type: APPL Creator: CCTL **********/

#define ControlDialogID 1000
#define nil 0L
/* important dialog items */
enum{   quitItem = 1,   setItem,   topPosItem,     leftPosItem, 
 bottomPosItem,  rightPosItem,   boxItem     };

  /* Our global variables */
DialogPtr ControlDialog;
Rect    boundsRect;

/**InitMacintosh()  Initialize all the managers & memory ***/
InitMacintosh()
{  MaxApplZone();
 InitGraf(&thePort);
 InitFonts();
 FlushEvents(everyEvent, 0);
 InitWindows();
 InitMenus();
 TEInit();
 InitDialogs(0L);
 InitCursor();
} /* end InitMacintosh */

/**GetBounds()  *  * Get the rect specified in dialog  ***/
GetBounds(theDialog)
DialogPtr theDialog;
{  Str255 str;   longdummy;

 boundsRect.top = GetETNum(theDialog, topPosItem);
 boundsRect.left = GetETNum(theDialog, leftPosItem);
 boundsRect.bottom = GetETNum(theDialog, bottomPosItem);
 boundsRect.right = GetETNum(theDialog, rightPosItem);
} /* end GetBounds */

/*TrackRect() Frame old, new bound rects in current GrafPort**/
TrackRect(oldRect, r)
Rect  *oldRect;
Rect  *r;
{  FrameRect(oldRect);
 FrameRect(r);
} /* end TrackRect */

/**DisplayBounds() Display a rect in the dialog*/
DisplayBounds(theRect, theDialog) 
Rect    *theRect;
DialogPtr theDialog;
{  SetETNum(theDialog, topPosItem, (long)theRect->top);
 SetETNum(theDialog, leftPosItem, (long)theRect->left);
 SetETNum(theDialog, bottomPosItem, (long)theRect->bottom);
 SetETNum(theDialog, rightPosItem, (long)theRect->right);
 SelIText(theDialog, topPosItem, 0, 32767);
} /* end DisplayBounds */

/**SetBoundsLoop() User drags to specify new rect**/
SetBoundsLoop(theDialog)
DialogPtr theDialog;
{  Rect oldRect;
 Rect   newRect;
 GrafPtrsavePort;
 GrafPtrdeskPort;
 Point  firstPoint;
 Point  secondPoint;
 Point  lastSecondPoint;

 GetPort(&savePort);
 OpenPort(deskPort = (GrafPtr)NewPtr(sizeof(GrafPort)));
 InitPort(deskPort);
 SetPort(deskPort);
 PenPat(gray);
 PenMode(notPatXor);
 PenSize(2, 2);
 while(!Button());
 GetMouse(&firstPoint);
 newRect.top = lastSecondPoint.v = firstPoint.v;
 newRect.left = lastSecondPoint.h = firstPoint.h;
 newRect.bottom = newRect.right = 0;
 while(Button()) {
 oldRect = newRect;
 GetMouse(&secondPoint);
 /* If the mouse location has changed then track mouse */
 if (secondPoint.v != lastSecondPoint.v || secondPoint.h != lastSecondPoint.h) 
 {
 /* Create a new Rect making sure it is not an empty Rect */
 if (secondPoint.v > firstPoint.v) {
 newRect.top = firstPoint.v;
 newRect.bottom = secondPoint.v;
 }
 else {
 newRect.top = secondPoint.v;
 newRect.bottom = firstPoint.v;
 }
 if (secondPoint.h > firstPoint.h) {
 newRect.left = firstPoint.h;
 newRect.right = secondPoint.h;
 }
 else {
 newRect.left = secondPoint.h;
 newRect.right = firstPoint.h;
 }
 lastSecondPoint = secondPoint;

 TrackRect(&oldRect, &newRect);
 DisplayBounds(&newRect, theDialog);
 }
 }
 FrameRect(&newRect);
 ClosePort(deskPort);
 DisposPtr((Ptr)deskPort);
 PenNormal();
 SetPort(savePort);
 boundsRect = newRect;
 } /* end SetBoundsLoop */

/*HandleControlDialog()  Main event loop  *  ****/
HandleControlDialog(theDialog)
DialogPtr theDialog;
{  EventRecord   event; /*  Filled by GetNextEvent */
 Booleanfinished = false; /*  Are we done? */
 int    chosen;
 char   theChar;

 while (!finished) /*  do this until we selected quit */
 { /* continue with the normal get next event stuff... */
 if (GetNextEvent(everyEvent, &event))
 /*  if there was an event... then  */
 {
 if (event.what == keyDown || event.what == autoKey)
 { 
 theChar = (char) (event.message & charCodeMask);
 switch(theChar) { 
 case ‘Q’:
 case ‘q’:
 case ‘.’:
 chosen = quitItem;
 event.what = 0; /* remove event */
 finished = true;
 ClickButton(theDialog, quitItem, 2);
   break;
   case ‘\t’:
 case ‘\b’: 
 break;
   case ‘\r’:
 case ‘\003’:
 case ‘S’:
 case ‘s’:
 chosen = setItem;
 event.what = 0; /* remove event */
 ClickButton(theDialog, setItem, true);
 SetBoundsLoop(theDialog);
 ClickButton(theDialog, setItem, false);
 break;
 default:
 if (theChar < ‘0’ || theChar > ‘9’)
 event.what = 0;
 break;
 }
 } else if (event.what == updateEvt)
 {
 SetPort(theDialog);
 BeginUpdate(theDialog);
 FrameItem(theDialog, boxItem);
 DrawDialog(theDialog);
 DrawDefaultBtn (theDialog, setItem);
 EndUpdate(theDialog);
 }
   }

 if (!finished) {
 if   (IsDialogEvent(&event))
 if (DialogSelect(&event, &theDialog, &chosen)) {
 GetBounds(theDialog);
 switch (chosen) {
 case 1:
 finished = true;
 break;
 case 2:
 ClickButton(theDialog, setItem, true);
 SetBoundsLoop(theDialog);
 ClickButton(theDialog, setItem, false);
 break;
 default:
 break;
 } /*  end of if switch  */
 } 
 HandleMouse(&boundsRect);
 } /*  end of if (!finished) */
 } /*  of event loop  */

 DisposDialog(theDialog);
} /* end HandleControlDialog */

/*****  * SetUpDialog()  *  * Set up dialog stuff  *  *****/
SetUpDialog() {
 int    itemType;
 Handle Hdl;

 ControlDialog = GetNewDialog(ControlDialogID, nil, -1L);
 CenterWindow(ControlDialog, &screenBits.bounds);
 DisplayBounds(&screenBits.bounds, ControlDialog);
 ShowWindow(ControlDialog);
 boundsRect = screenBits.bounds;
 HandleControlDialog(ControlDialog);
} /* end SetUpDialog */

/*****  * main()  *  * Call the main procedures  *  *****/
main()

{  InitMacintosh();
 SetUpDialog();
} /* end main */
Listings:  Functions.C

/****
 * GetEText()
 * Get text of an ETItem
 ****/
GetEText (theDialog, theItem, s)
DialogPtr theDialog;
inttheItem;
char    *s;
{
 int     theType;
 Handle Hdl;
 Rect box;

 GetDItem (theDialog, theItem, &theType, &Hdl, &box);
 GetIText (Hdl, s);
} /* end GetEText */

/****
 * GetETNum()
 * Get number from an ETItem
 ****/
GetETNum(theDialog, theItem)
DialogPtr theDialog;
inttheItem;
{
 Str255 s;
 long theNum;
 
 GetEText(theDialog, theItem, &s);
 StringToNum(s, &theNum);
 return(theNum);
} /* end GetETNum */

/****
 * SetEText()
 * Set text of an ETItem
 ****/
SetEText (theDialog, theItem, s)
DialogPtr theDialog;
inttheItem;
Str255  s;
{
 int     theType;
 Handle Hdl;
 Rect box;

 GetDItem (theDialog, theItem, &theType, &Hdl, &box);
 SetIText (Hdl, s);
} /* end SetEText */

/****
 * SetETNum()
 * Set number in an ETItem
 ****/
SetETNum(theDialog, theItem, theNum)
DialogPtr theDialog;
inttheItem;
long    theNum;
{
 Str255 s;
 
 NumToString(theNum, s);
 SetEText(theDialog, theItem, &s);
} /* end GetETNum */

/***** LToGRect()  Convert a local rect to global *****/
LToGRect(r)
Rect  *r;
{
 Point  pt1,
 pt2;

 pt1 = topLeft(*r);
 pt2 = botRight(*r);
 LocalToGlobal(&pt1);
 LocalToGlobal(&pt2);
 Pt2Rect(pt1, pt2, r);
} /* end LToGRect */

/*****
 * CenterWindowPoint()
 * Calculates the topleft co-ords of a window,
 * taking screen size into account
 *****/
Point CenterWindowPoint (theRect)
Rect  *theRect;
{
 int    theInd = (screenBits.bounds.bottom<350) ? 3:4;
 Point  thePt;
 int    int1, int2;

 int1=((screenBits.bounds.right-screenBits.bounds.left-theRect->right+theRect->left) 
/ 2);
 int2=((screenBits.bounds.bottom-screenBits.bounds.top-theRect->bottom+theRect->top+20) 
/ theInd);
 SetPt(&thePt, int1, int2);
 return(thePt);
} /* end CenterWindowPoint */

/*****
 * CenterWindow()
 * Centers a dialog or window
 *****/
void CenterWindow(theDialog)
DialogPtr theDialog;
/* Center window - center slightly higher for large screens */
{
 Point  thePt;
 Rect newBounds;

 newBounds = *&theDialog->portRect;
 LToGRect(&newBounds);
 thePt = CenterWindowPoint(&newBounds);
 MoveWindow(theDialog, thePt.h, thePt.v, 0);
} /* end CenterWindow */

/****ClickButton() Simulate a click in a button ****/
ClickButton(theDialog, ID, method) 
/* 0 is off, 1 is on, 2 simulates a click */
DialogPtr theDialog;
intID;
intmethod;
{
 int    itemType;
 Handle item;
 Rect box;
 long ticks;

 GetDItem(theDialog, ID, &itemType, &item, &box);
 HiliteControl((ControlHandle) item, (method >= 1));
 if (method >= 2)
 {
 Delay(8L, &ticks);
 HiliteControl((ControlHandle) item, 0);
 }
} /* end ClickButton */

/****
 * FrameItem()
 * Frame a dialog item in current pen modes
 ****/
void FrameItem (theDialog, item)
DialogPtr theDialog;
intitem;
{
 int    optType;
 Handle btnHdl;
 Rect   optBox;

 SetPort(theDialog);
 GetDItem(theDialog, item, &optType, &btnHdl, &optBox);
 FrameRect(&optBox);
} /* end FrameItem */

/**** DrawDefaultBtn() Outline the default button ****/
void DrawDefaultBtn (theDialog, item)
DialogPtr theDialog;
intitem;
{
 int    optType;
 Handle btnHdl;
 Rect   optBox;

 SetPort(theDialog);
 GetDItem(theDialog, item, &optType, &btnHdl, &optBox);
 PenSize(3, 3);
 InsetRect(&optBox, -4, -4);
 FrameRoundRect(&optBox, 16, 16);
} /* end DrawDefaultBtn */
Listing:  MousePos.C

/********
* MousePos()
* Set the mouse position, August 22, 1989
* by Robert S. T. Gibson for MacTutor
********/
void MousePos(newPos)
Point newPos;
{
 int    *MTemp;
 char *CrsrNew;
 int    i;

 MTemp = (int *)  0x828;  /* Set up our globals... */
 CrsrNew = (char *) 0x8CE;

/* Points are stored as (row, column) or (v, h) in memory...*/
 /* Set our globals... */
 for (i=0;i<3;i++) {
 *(MTemp+2*i) = newPos.v;
 *(MTemp+2*i+1) = newPos.h;
 }
 *CrsrNew = -1;  /* There’s a new position */
}
 

Community Search:
MacTech Search:

Software Updates via MacUpdate

CrossOver 14.1.3 - Run Windows apps on y...
CrossOver can get your Windows productivity applications and PC games up and running on your Mac quickly and easily. CrossOver runs the Windows software that you need on Mac at home, in the office,... Read more
Little Snitch 3.5.3 - Alerts you about o...
Little Snitch gives you control over your private outgoing data. Track background activity As soon as your computer connects to the Internet, applications often have permission to send any... Read more
OmniGraffle Pro 6.2.3 - Create diagrams,...
OmniGraffle Pro helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use... Read more
OmniFocus 2.2 - GTD task manager with iO...
OmniFocus helps you manage your tasks the way that you want, freeing you to focus your attention on the things that matter to you most. Capturing tasks and ideas is always a keyboard shortcut away in... Read more
Cocktail 8.4 - General maintenance and o...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
PDFKey Pro 4.3 - Edit and print password...
PDFKey Pro can unlock PDF documents protected for printing and copying when you've forgotten your password. It can now also protect your PDF files with a password to prevent unauthorized access and/... Read more
Kodi 15.0.beta1 - Powerful media center...
Kodi (was XBMC) is an award-winning free and open-source (GPL) software media player and entertainment hub that can be installed on Linux, OS X, Windows, iOS, and Android, featuring a 10-foot user... Read more
DiskCatalogMaker 6.4.12 - Catalog your d...
DiskCatalogMaker is a simple disk management tool which catalogs disks. Simple, light-weight, and fast. Finder-like intuitive look and feel. Super-fast search algorithm. Can compress catalog data... Read more
Macs Fan Control 1.3.0.0 - Monitor and c...
Macs Fan Control allows you to monitor and control almost any aspect of your computer's fans, with support for controlling fan speed, temperature sensors pane, menu-bar icon, and autostart with... Read more
Lyn 1.5.11 - Lightweight image browser a...
Lyn is a lightweight and fast image browser and viewer designed for photographers, graphic artists and Web designers. Featuring an extremely versatile and aesthetically pleasing interface, it... Read more

Moleskine Timepage – Calendar for iCloud...
Moleskine Timepage – Calendar for iCloud, Google & Exchange 1.0 Device: iOS iPhone Category: Productivity Price: $4.99, Version: 1.0 (iTunes) Description: The most elegant calendar for your pocket and wrist, Timepage is a... | Read more »
QuizUp Gets Social in its New Update
Plain Vanilla Corp has released a new and improved version of their popular trivia game, QuizUp. The app now emphasizes social play so you can challenge friends from all over the world. [Read more] | Read more »
The Deep (Games)
The Deep 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Swipe Controls Delve into the deep in this retro rogue-like! Swipe to move your diver around and keep away from the enemies as you... | Read more »
Battle of Gods: Ascension (Games)
Battle of Gods: Ascension 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: TURN-BASED TACTICAL COMBATFight tactical battles against the forces of Hades! In Battle of Gods: Ascension you play... | Read more »
Shadowmatic's Latest Update Adds a...
Shadowmatic's shadowy shadow-ness is getting a little shadowy-er thanks to a recent update that adds an Arcade Mode. [Read more] | Read more »
Sunrise Calendar and Slack Have Assimila...
Wunderlist is perhaps one of the most populat and beloved productivity apps on the App Store - and now it's gone and incorporated itself into other useful services like Sunrise Calendar and Slack. [Read more] | Read more »
Crossy Road Devs Hipster Whale are Bring...
Hipster Whale, the minds behind the rather popular (and rather great) Crossy Road, have teamed-up with Bandai Namco to create PAC-MAN 256: an absolutely bonkers looking maze runner chaser thing. | Read more »
Meet the New Spotify Music
Spotify Music  has a lot going on. They're introducing 3 new modes to serve all your musical needs, with the "Now" start page  gives you curated playlists based on your particular tastes. As you listen the app will learn more about your tastes and... | Read more »
What the Apple Watch Gets Right, and Wha...
| Read more »
Celebrate PAC-MAN's 35th Birthday W...
BANDAI NAMCO Entertainment America is celebrating PAC-MAN's 35th anniversary by releasing updates for PAC-MAN and PAC-MAN Lite for iOS. [Read more] | Read more »

Price Scanner via MacPrices.net

What Would the ideal Apple Productivity Platf...
For the past four years I’ve kept a foot in both the Mac and iPad camps respectively. my daily computing hours divided about 50/50 between the two devices with remarkable consistency. However, there’... Read more
PageMeUp 1.2.1 Ten Dollar Page Layout Applica...
Paris, France-based Softobe, an OS X software development company, has announced that their PageMeUp v. 1.2.1, is available on the Mac App Store for $9.99. The license can be installed on up to 5... Read more
Eight New Products For USB Type-C Application...
Fresco Logic, specialists in advanced connectivity technologies and ICs, has introduced two new product families targeting the Type-C connector recently introduced across a number of consumer... Read more
Scripps National Spelling Bee Launches Buzzwo...
Scripps National Spelling Bee fans can monitor the action at the 2015 Spelling Bee with the new Buzzworthy app for iOS, Android and Windows mobile devices. The free Buzzworthy app provides friendly... Read more
13-inch 2.5GHz MacBook Pro on sale for $120 o...
B&H Photo has the 13″ 2.5GHz MacBook Pro on sale for $979 including free shipping plus NY sales tax only. Their price is $120 off MSRP, and it’s the lowest price for this model (except for Apple’... Read more
27-inch 3.3GHz 5K iMac on sale for $1899, $10...
B&H Photo has the new 27″ 3.3GHz 5K iMac on sale for $1899.99 including free shipping plus NY tax only. Their price is $100 off MSRP. Read more
Save up to $50 on iPad Air 2, NY tax only, fr...
B&H Photo has iPad Air 2s on sale for up to $50 off MSRP including free shipping plus NY sales tax only: - 16GB iPad Air 2 WiFi: $469 $30 off - 64GB iPad Air 2 WiFi: $549.99 $50 off - 128GB iPad... Read more
Updated Mac Price Trackers
We’ve updated our Mac Price Trackers with the latest information on prices, bundles, and availability on systems from Apple’s authorized internet/catalog resellers: - 15″ MacBook Pros - 13″ MacBook... Read more
New 13-inch 2.9GHz Retina MacBook Pro on sale...
B&H Photo has the 13″ 2.9GHz/512GB Retina MacBook Pro on sale for $1699.99 including free shipping plus NY tax only. Their price is $100 off MSRP, and it’s the lowest price for this model from... Read more
Apple refurbished 2014 MacBook Airs available...
The Apple Store has Apple Certified Refurbished 2014 MacBook Airs available starting at $679. An Apple one-year warranty is included with each MacBook, and shipping is free: - 11″ 1.4GHz/128GB... Read more

Jobs Board

Senior Software Engineer - *Apple* SIM - Ap...
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
Lead *Apple* Solutions Consultant - Retail...
**Job Summary** Job Summary The Lead ASC is an Apple employee who serves as the Apple business manager and influencer in a hyper-business critical Reseller's store Read more
Architect / Senior Software Engineer, *Apple...
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* Pay Support Readiness Project Manage...
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
Hardware Design Validation Engineer - *Apple...
**Job Summary** The Apple Watch team is looking for a Hardware Design Validation Engineer. This person will be part of the Apple Watch hardware team with Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.