Re: What units are in effect when drawing?
Re: What units are in effect when drawing?
- Subject: Re: What units are in effect when drawing?
- From: publiclook <email@hidden>
- Date: Sat, 5 Apr 2003 18:27:39 -0500
The whole point of basing the coordinate system on a "real" unit like
points, inches, millimeters, or miles is that it is device independent.
Any drawing based on pixels will be wrong an any device that uses
different sized pixels. Using (Postscript) points as units is a large
part of what makes Display Postscript (I mean Display PFD) (I mean
Quartz 2D) device independent. It works equally well on low resolution
monitors and on 1200 dpi laser printers and on 2000 dpi film.
The fact that Apple chooses to pretend that pixels on your display are
1 point square whether they really are or not is a convenience and an
optimization. In the future, Apple might provide a way to tell Quartz
what you think the real resolution (size of a pixel) on you display is.
Then Quartz can draw a 72 point wide line so that it is an inch wide as
measured with a ruler pressed against your display. In the mean time, a
72 point wide line will continue to be an inch wide on the 1200 dpi
printer because a point is a point is a point as long as the true
resolution of a device is known.
On Saturday, April 5, 2003, at 02:58 PM, Chris Hanson wrote:
At 7:05 PM +0300 4/5/03, Janek Priimann wrote:
> What are the default units when drawing in a custom view? Picas?
Points? mm?
The default units are points.
But because all the macintosh computers use 72dpi resolution
and 1 inch equals to 72 points then 1 point = 1 pixel.
However, you shouldn't necessarily assume this.
IBM has been shipping a 24-inch 200dpi LCD display for a year now, and
ViewSonic is OEMing it. I suspect its price will come down to the
level of the original Cinema Display soon. Other vendors are also
increasing display density rapidly.
I have no idea what Apple's future plans are for CoreGraphics (and
couldn't say if I did know), but I suspect at some point in the next
few years we'll see true resolution independence in the display
architecture. I'd rather my code Just Work when that comes about.
Also, you can't assume one point is equal to one pixel when your view
is printing. After all, on a 1200dpi printer, a one by one point dot
is 16.7 by 16.7 "pixels"...
-- Chris
--
Chris Hanson, bDistributed.com, Inc. | Email: email@hidden
Custom Application Development | Phone: +1-847-372-3955
http://bdistributed.com/ | Fax: +1-847-589-3738
http://bdistributed.com/Articles/ | Personal Email: email@hidden
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