Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!ASC.SLB.COM!rxb
From: rxb@ASC.SLB.COM (Rafael Bracho)
Newsgroups: comp.windows.news
Subject: Re:  Open Windows
Message-ID: <8912271740.AA04243.rxb@plutonium.ASC.SLB.COM>
Date: 29 Dec 89 17:32:24 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 56

Re: doc%jalapeno.UUCP%fajita.UUCP@suntan.West.Sun.COM (Tom Dockery)'s
    message

>The answer is somewhat simple:  it's rather difficult to scale everything
>appropriately to handle differing device densities if your have no way
>of determining those densities.  As most (though certainly not all)
>monitors do not have any provisio for providing this information to the
>framebuffer (and most framebuffers wouldnt know what to do with it anyway),
>certain assumptions have to be made about the attached devices in advance.
>In our shop, we regularly swap 16 and 19 inch color monitors around.  On
>a Sun cg-3 these both have a resolution of 1152 X 900;  this means the 16
>inch monitor has a higher density of pixels per unit measure in either
>dimension than the 19 inch.

I agree with you in that it's impossible to find out actual monitor
size.  I still agree with Peter's original message in that the server
should change the default matrix between an 1152 x 900 and a 1600 x 1280
framebuffers, so the same PostScript program should produce the same
sized windows, on the same size monitors, regardless of framebuffer
resolution.

>The basic unit of measure in PostScript is the point, 1/72 of an inch; not
>too metric, to be sure, but having a basis in the printing industry.  If
>the PostScript (or NeWS) programmer knows, or can query, the density of
>the device to be driven, s/he can transform everything accordingly, so that
>the same PS source prints to the same result on a 300 or 900 dpi printer.
>The higher density printer then simply provides just that.  If the
>programmer can neither know in advance, nor find out a run-time by query
>the density of the output device, however, s/he faces a quandry.  There
>is no real way, short of modifying the hardware, to solve the problem in a
>device independent way ...

I must disagree with you.  The same PostScript source will produce the
same output, without any resolution inquiries, providing the interpreter
sets the default transformation matrix such that the default coordinate
system is still 1/72's of an inch per unit (not quite points, but close
enough).  Thus the program:

	gsave
	0 setgray
	/Helvetica findfont 14 scalefont setfont
	144 144 scale
	1 1 translate
	(Hello there!) show
	showpage
	grestore

will produce a page with the string "Hello there!"  in 14 point
Helvetica, 2 inches above and 2 inches to the right of the lower left
corner, *independently* of the printer's resolution.

Note that it is possible to get in trouble by using 'setmatrix' instead
of 'translate' and 'scale', particularly if one is not careful.

					Rafael Bracho
					rxb@asc.slb.com