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Re: Question: units of AppKit coordinates.


From: Chris Hanson
Subject: Re: Question: units of AppKit coordinates.
Date: Wed, 15 Oct 2003 19:00:13 -0500

On Wednesday, October 15, 2003, at 06:47  PM, Vaisburd, Haim wrote:
AppKit accepts coordinates as floating point numbers.
I have drawn a conclusion that they are probably meant
to be some device-independent units like millimeters
or inches or something alike.

Coordinates should probably be kept as floating point right up until the point they're sent to the back-end.

User-space coordinates in AppKit are considered to be in PostScript points, *unless you change the coordinate system*. In PostScript, there are 72 points to the inch. This is close (but not exactly equal) to the typographer's point; there are just over 72 typographer's points to the inch.

It should be up to the back-end to translate device-independent coordinates into device-dependent coordinates for the particular output device in use. This is going to be particularly important in the near future as users start getting 200dpi displays. (The cost of a 24-inch 200dpi widescreen LCD monitor is already down to US$4000 from ViewSonic or IBM.)

  -- Chris

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Custom Mac OS X Development           |  Phone: +1-847-372-3955
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