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From: raveling@venera.isi.edu (Paul Raveling)
Newsgroups: comp.windows.x
Subject: Re: Handling expose events.
Message-ID: <9415@venera.isi.edu>
Date: 23 Aug 89 17:48:52 GMT
References: <8908220058.AA08564@mote.umb.edu> <8908221732.AA28636@gaak.LCS.MIT.EDU>
Reply-To: raveling@venera.isi.edu (Paul Raveling)
Organization: Information Sciences Institute, Univ. of So. California
Lines: 37


	[original message not forwarded -- appears to be a response
	to a message I missed about finding a good technique to handle
	redrawing in response to an expose event]


	An easy technique with X11 (other than backing store) is
	to draw into a pixmap instead of the window, drawing only
	when necessary, and do an XCopyArea from pixmap to window.
	The XCopyArea is quite fast on our systems -- virtually
	instantantaneous on our HP 9000/370's.

	Code to respond to an Expose event is then quite simple.
	Here's a fragment from the X11 interface in our imglib source:


expose = (XExposeEvent *) &sir -> event;	/*  Point to event data	  */
	...

	switch ( (sir->event).type )
	    {
	    case Expose:	/*  Expose:  Copy area from pixmap	*/

		XCopyArea ( X11_env->display, sir->pix, sir->win, X11_env->gc,
			expose->x, expose->y, expose->width, expose->height,
			expose->x, expose->y );
		break;

	    case NoExpose:	/*  A couple noise events...		*/
	    case GraphicsExpose:
		...



----------------
Paul Raveling
Raveling@isi.edu