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From: dolf@fwi.uva.nl (Dolf Starreveld)
Newsgroups: comp.sys.mac.misc
Subject: Re: Centering Dialog Boxes on the Macintosh
Message-ID: <1229@carol.fwi.uva.nl>
Date: 5 Sep 90 23:01:16 GMT
References: <11818@chaph.usc.edu>
Sender: news@fwi.uva.nl
Lines: 73

talcott@nunki.usc.edu (Adam Talcott) writes:
> ... Deleted ...
> and two thirds of the screen below.  My problem is I can center the border of
> the dialog to conform to these standards, but the contents of the dialog box
> do not move!!  What do I do to move this?  The following are the lines of code
> I use (in THINK C):
I cleaned this up a bit and inserted modifications in the right place(s).

> CenterDialogwhichDialog
> DialogPtr	whichDialog;
> {
>    Rect   dialogRect;
>    int    dialogWidth, dialogHeight, screenWidth, screenHeight;
-->  int    spaceWidth, spaceHeight;
> 	
>    if whichDialog != NIL_POINTER
>    {
>      screenWidth = screenBits.bounds.right - screenBits.bounds.left;
>      screenHeight = screenBits.bounds.bottom - screenBits.bounds.top;
>      dialogWidth = whichDialog->portRect.right - whichDialog->portRect.left;
>      dialogHeight = whichDialog->portRect.bottom - whichDialog->portRect.top;
> 		
-->    /* Compute amount of space on both sides */
-->    spaceWidth = screenWidth - dialogWidth;
-->    spaceHeight = screenHeight - dialogHeight;
-->
-->    /* Now move the dialog window to centered position according to rules */
-->    MoveWindow(whichDialog,
-->	  screenBits.bounds.left + spaceWidth / 2, /* Halfway horiz. */
-->	  screenBits.bounds.top + spaceHeight / 3);/* 1/3 from top */
>    }
> }

There is a clear, but sometimes vague relationship between a window's
portRect, the boundsRect of its portBits and the position of a window.
Assume that screenBits.bounds are (0,0) - (large, large).
If a window's top left corner is at 100, 100 in global (screen) coordinates,
its bitmap (portBits) is still the screen itself. On the other hand, the
bounds rectangle of the bitmap relative to the window's top left corner is
now (-100, -100) (large - 100, large - 100). This way, when QuickDraw draws
anything in the window's bitmap it appears at the right place. Drawing at 0,0
in this bitmap, will actually by a place offset 100 pixels in both way from
the top left of the screen bitmap and will hence appear in the top left corner
of the window.
However, all drawing in a grafport occurs within the rectangle defined by
portRect, expressed in the coordinates of the portBits.bounds rectangle.

If you directly change the portRect coordinates you are effectively changing
the coordinate system for all subsequent drawing in that grafPort.
The window itself is drawn with another grafport, the so called window
manager grafport, which ytou didn't change. Besides, you can not move
a window on the screen, just by changing some coordinates.
As a side effect of your change, subsequent drawing inside the window
will occur in unexpected locations. You can force this drawing by overlaying
with something else, but since you are in a dialog, you'l;l probably need
an FKEY that pops up a window to do that.

The reason I add screenBts.left, resp .top in the above MoveWindow call is
that thos are not necessarily 0. In multiy screen environments the may
be different.
If you really want things to be all right you should also take the menu bar
and its heigth into account. Note however, that in multiscreen environments
not all screens have one (but since you center against screenBits.bounds you
will always center on the main screen) and the a menubar is not always 20
pixels high, but that's another subject.

--dolf

--
Dolf Starreveld  Phone: +31 20 592 5056/5022 (FAX: 5155), TELEX: 10262 HEF NL
EMAIL:           dolf@fwi.uva.nl (dolf%fwi.uva.nl@hp4nl.nluug.nl)
SNAIL:           Dept. of Math. and Computing Science, University of Amsterdam,
                 Kruislaan 409, NL-1098 SJ  Amsterdam, The Netherlands