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From: hawley@adobe.COM (Steve Hawley)
Newsgroups: comp.sys.mac.programmer
Subject: Re: How does one detect whether a modifier key is being held down?
Keywords: Modifier key
Message-ID: <7919@adobe.UUCP>
Date: 2 Nov 90 17:28:23 GMT
References: <5467@quiche.cs.mcgill.ca>
Reply-To: hawley@adobe.UUCP (Steve Hawley)
Organization: Adobe Systems Incorporated, Mountain View
Lines: 54

In article <5467@quiche.cs.mcgill.ca> monching@quiche.cs.mcgill.ca (Patrick WONG) writes:
>Does anyone know if you can detect whether a modifier key is held down
>without having to press a character key or clicking the mouse?
>
>I know this is possible because MacPaint II will change the arrow to a
>hand for option key and magifying glass for a command key.
>
>I wish to do the samething.  Can't seem to find anything in Inside Mac.

Look in Volume I on page 259.  The procedure GetKeys() returns the current
state of the keyboard.  In order to read it you could write something like
this:

IsThisKeyDown(keyCode)
register unsigned short keyCode;
{
	unsigned char myKeys[16];
	static unsigned char bits[8] = {
		0x80, 0x40, 0x20, 0x10, 0x8, 0x4, 0x2, 0x1
	};

	GetKeys(myKeys);

	/* Address the bit in the key map.  The array "bits" might be
	 * reversed.  Try it out and see.
	 */
	return( (myKeys[keyCode / 8] & bits[keyCode % 8] ) != 0);
	/* if you want to play the efficiency game, you may want to
	 * rewrite this as:
	 * return( myKeys[keyCode >> 3] & bits[keyCode & 7]);
	 * which is equivalent code (albeit less readable) and will
	 * compile to more efficient code in Think C.
	 */
}

/* These values are take directly from inside Mac Volume I, page 251.  Please
 * note that the keymap values are different for many of the keys on
 * international keyboards!  Fortunately, the modifier keys are the same,
 * so the chances of the code retaining future compatability are good.
 * An example of a program that failed in the task is MacLanding (a shareware
 * Defender knockoff) that depended on the "Enter" key code staying the same.
 * It changed for the MacPlus and on, so the game doesn't play right.  Oops!
 */
#define IsOptionDown() IsThisKeyDown(58)
#define IsCommandDown() IsThisKeyDown(55)

Good luck.

Steve Hawley
hawley@adobe.com
-- 
"I'm sick and tired of being told that ordinary decent people are fed up with
being sick and tired.  I know I'm certainly not, and I'm sick and tired of
begin told that I am." -Monty Python