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Cursor Control 1
Volume Number:6
Issue Number:6
Column Tag:abC

Related Info: TextEdit Quickdraw

Cursor Control

By Bob Gordon, Minneapolis, MN

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

Managing Cursors

I know how to curse

Shakespeare, The Tempest (Act 1, Scene 2)

If you remember from last time, I had introduced the idea of adding some additional data structures at the end of the window record to aid in keeping track of the data that hangs around with a window. At the end of that article I said we would illustrate the use of the added data in managing the cursor. We will cover that, but first I would like to comment on a nice piece of work by John Nairn in the April issue.

John has presented a full-blown Scrolling Manager to handle all the issues involved with creating and maintaining scrolling windows. While there are a number of differences between what he has done and what I am describing in this column, a couple common points are worth mentioning. First, the approach is to isolate the user interface control from the actual application. That is, as much as possible, develop generic code to handle the basic operation of the windows (or menus or dialogs, for that matter). Second, this generic code will probably require some place to keep the information it uses; develop a data structure to hold this, and attach it in some way to the window (or menu or dialog). There is actually a bit more commonality (I have the advantage of being able to see the parts I have written but not yet published), and we will explore one of those in this article.

One point of difference. John uses the window’s refCon to hold his additional data structure. His new data structure includes its own refCon for the window’s contents. I added the data on to the end of the window’s structure itself. I feel this simplifies things somewhat, and at least for now it does not seem to violate any rules. If you liked John’s article as I did, you certainly have my permission to use the technique I’ve outlined in implementing it. While I haven’t met John, I’m reasonably sure he won’t mind.


The cursor attached to the mouse changes its shape as you move the mouse around the screen. In addition, the user can often affect its shape directly by selecting a tool from a toolbox (usually found in graphics or page layout applications). The problem we deal with this month is how to manage the cursor so it is handled as automatically as possible.

The first issue is getting cursors. There are five built in to the Mac: arrow, crosshairs, plus, clock, i-beam. You can also make your own with ResEdit or some other resource tool. Once we have decided the cursors to use (and made their resources), we need to control the appearance on the screen. What I will describe this month is one way to manage the change of cursor shape as the user moves the mouse around the screen. I am not covering the setting of the cursor’s via tool box or menus.

In June I suggested the use of window margins. The window margin is that area between the window’s frame, which is handled by the Macintosh toolbox routines, and the window’s actual contents, which is what your application is about. The objects that might be in a window margin include scroll bars, rulers, and tool boxes. These are such common components of windows that they can be handled by generic code apart from your application. The other property of the window margin is that the cursor typically changes into the arrow as it is moved into the scroll bar, ruler, etc.


Cursorhelp consists of three functions and an include file to aid in the setting and automatic changing of cursors. These functions assume the window structure described in June. The window margins (mtop,mbottom, mright, mleft) are stored with the window. More importantly, the rectangle that surrounds the actual window contents (cursrt) is also stored (I assume rectangular windows). This rectangle is the area in which the cursor is the shape the user selected (i beam, cross, etc.). I put it in the window structure simply to avoid having to calculate it each time. The final piece is the cursor itself (mouser). That is, the cursor’s shape as selected by the user is a property of the window. With a multi-window application the user can have one window editing text, another editing a graphic, and a third editing a spreadsheet (I am not suggesting anyone actually write something like this), and the appropriate cursor will be displayed automatically as the user selects each window. The main loop need know nothing of the cursors.

The main loop does need to set the cursor. There are two places where this can occur: the users specifies a cursor in some way or, the application displays the watch (or other indicator) to indicate the passage of time. The program calls CursorToUse passing the window and the number of the desired cursor.

The program also needs to set the cursor rectangle. This must be done every time the window’s size is changed or the window margins are changed (for example, choosing to show rulers or not).A call to CursorRect() does that. Note that the window margins must have been previously set.

To actually control the cursor, the program calls CursorMaintain() as it runs through the event loop.

Include Files
/*windowhelp.h */
#include “TextEdit.h”
#include“abc.h”    /* window add-on structure */

#define WindowStruct struct w_struct
 WindowRecord  wr;  /* the original window record */
 uchar  mtop;    /* margin indents */
 uchar  mleft;
 uchar  mbottom;
 uchar  mright;
 Rect   cursrt;    /* used for cursor control */
 char   mouser;  /* mouse pointer id  */
 char   changed; /* if contents were changed */
 long   ckind;   /* kind of contents */
 short  fileref; /* associated file, if any */
 TEHandle curtext; /* handle to current text */

#define Woffset  18
#define SBarWidth 15

/* these definitions allow easy generation of the four square cornered 
titled windows. The basic (simplest) window is the WDOC (NoGrowDocProc). 
To this optionally add WGROW to add a grow box and/or WZOOM to add a 
zoom box.
#define WDOC4
#define WGROW    -4
#define WZOOM    8
#define WVBAR    16
#define WHBAR    32

/* Value placed in windowKind field of WindowRecord by WindowNew if the 
window has a grow box. This is used by routines that redraw the window 
to decide whether to draw the grow box or not 
#define HASGROW  9


/* cursorhelp.h
 * header file for cursorhelp
 #defineARROW  0
 #defineIBEAM  1
 #defineCROSS  2
 #defineWATCH  4
CursorHelp Functions

/* CursorMaintain
 * Adjusts the cursor according to the value
 * set in the window and the rectangle currect.
 * If the mouse is in the rectangle, the cursor 
 * set to the current cursor, otherwise it is
 * set to the arrow.
 * The if statement checks to see if there is a 
 * valid window and if the window belongs to the
 * application. If it does not belong to the application
 * it is a DA. If the DA is controlling the cursor, there
 * will be a conflict as both programs attempt to control
 * it.
 WindowStruct  *ws;
 Point  pt;
 CursHandle curs;
 short  curcursor; /* current cursor */
 if (ws && (((WindowRecord *)ws)->windowKind > 7) )
 curcursor = ws->mouser;  /* cursor kind is stored in the window struct 
 if ((PtInRect(pt, &(ws->cursrt))) && (curcursor))
 curs = (Cursor **)GetCursor(curcursor);     
 else if (curcursor != WATCH)
 if (ws == NIL)

/* CursorRect
 * Uses the portRect of the window passed in
 * to set the current rectangle.  Adjusts the size
 * of the rectangle to account for window margins.
 * By keeping the rectangle around, we eliminate doing
 * this each time through the event loop.
 WindowStruct    *ws;
 ws->cursrt = ((GrafPort *)ws)->portRect;

/* CursorToUse
 * Sets the cursor to be displayed in the
 * rectangle of the current window.
 * Either pass a pointer to the window struct
 * or a NULL pointer. If a NULL pointer is passed,
 * CursorToUse() will use the front window. 
 * Note: At least one window must exist for this
 * to work, but if no windows exist, it
 * will not hurt.
 WindowStruct  *ws;/* window struct to set cursor for */
 short  c;/* cursor code to use */
 if (!ws)
 ws = (WindowStruct *)FrontWindow();
 if (ws)
 ws->mouser = c;

Using CursorMaintain()

The following fragment shows the call to CursorMaintain() in the main event loop.

 char   c;
 short  windowcode;
 WindowStruct  *ws;
 wp = FrontWindow();
 if (wp)
 if (GetNextEvent(everyEvent,&theEvent))

Other Comments

Check John Nairn’s article for other things to do to automate cursor control. You will note he checks for certain keys being pressed to change the cursor to allow window scrolling (e.g. with a hand).

Last Time

I have a minor error in June’s column. I included some space in the window structure to handle window zooming. These are not needed as zooming is fully supported by the Mac Toolbox. I hadn’t used them for anything yet.

Next Time

Next time I am going to show a quick and very dirty way to help deal with menus.

P.S. Comments are welcome. Send your notes to MacTutor, and please include a phone number.


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