Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!nosc!ucsd!ucbvax!hplabs!well!wdh
From: wdh@well.UUCP (Bill Hofmann)
Newsgroups: comp.sys.mac.programmer
Subject: Re: how do I find bit-depth of a window?
Summary: Read Vol 5: Graphic devices (GetMaxDevice, gdHandles)
Keywords: QuickDraw BitMap PixMap
Message-ID: <6641@well.UUCP>
Date: 27 Jul 88 16:15:09 GMT
References: <2127@uhccux.uhcc.hawaii.edu>
Reply-To: wdh@well.UUCP (Bill Hofmann)
Organization: Whole Earth 'Lectronic Link, Sausalito, CA
Lines: 40

>#1: Given a window, and a Rect in that window's coordinates, how can I tell
>if that rectangle's contents are currently displayed on a single monitor
>with one-bit color, addressable as an old-style BitMap?

First, convert the rect to global coords (by being sure the window is
the current port, then, by doing LocalToGlobal on the topLeft and botRight
points of the Rect.  Then, do a GetMaxDevice(&yourRect), which will return
the deepest device that intersects your rect (it returns a GDHandle). E.g.:

	if (deepest = GetMaxDevice(&yourRect))	/* in case NO device matches */
	{
		if ((*(*deepest)->gdPMap)->pixelSize == 1)
			/* use the pixmap's baseAddr */ ;
	}

>#2: If that rectangle is indeed addressable as a BitMap, but the window
>overlaps several monitors, how do I find the address for the Rect in
>question?

	Once you've done the above, you've got the pixmap for the 1 bit
	device that your window rect is on.  Somewhere in the depths of
	Vol 5 they mention which device the portBits points to-but it
	is pretty much ignored by color QD, as I recall.  I think it's
	the first device on the list that the window's in, or maybe the
	main device, but don't quote me.

	So once you've found the device, you've got the pixmap, and
	thus you have your address (somewhere in NuBus space) and you
	have *your* rect (in global coords) and from the device, you
	can get the rect *it* represents ((*deepest)->gdRect), then
	you can intersect the two, and use your head to figure the
	address, given the rowBytes and etc.  Beware: if you muck with
	the gdRect, you can really screw things up (speaking from 
	experience).  Note esp. that rowBytes MUST be used, not other
	indicators of screen width.

So how is it that MacDTS refuses to answer technical questions 3 weeks
before MacWorld?  Seems like an ill-guided policy to me (I've got at
least one fairly burning question in the queue...).

-Bill Hofmann