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From: fry@huma1.UUCP
Newsgroups: comp.sys.mac
Subject: Re: How Many Colors?
Message-ID: <2928@husc6.UUCP>
Date: Sat, 3-Oct-87 21:14:10 EDT
Article-I.D.: husc6.2928
Posted: Sat Oct  3 21:14:10 1987
Date-Received: Sun, 4-Oct-87 07:08:19 EDT
References: <2927@husc6.UUCP>
Sender: news@husc6.UUCP
Reply-To: fry@huma1.UUCP (David Fry)
Organization: Harvard Math Department
Lines: 24
Keywords: Color, QuickDraw, Depth

In article <2927@husc6.UUCP> singer@endor.UUCP (Richard Siegel) writes:
>How does one tell how many bits per pixel are set in the Control Panel?
>I know that it's possible, because I see demos that refuse to run
>unless 8 bits per pixel (256 colors) are set up -- they display a
>message saying "8 bits per pixel required" if it isn't set up.

Let screenRect be a rectangle that defines the area you want
to know the pixel depth of.  If you only have one monitor
attached then screenRect can be screenBits.bounds, but you may
want to be more specific for multiple monitors.  If you just
want to know the greatest depth of any monitor attached (which
is the normal thing to do) let screenRect be the rectangle
enclosing the GrayRgn, the desktop even for multiple screen
setups.

Once you've got screenRect figured out, call 
maxdev = GetMaxDevice(&screenRect);
    /* returns gDevice handle of deepest device */

and then

theDepth = (**((**maxdev).gdPMap)).pixelSize;

will give you the bits per pixel of that screen.