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From: don@BRILLIG.UMD.EDU (Don Hopkins)
Newsgroups: comp.windows.news
Subject: Is "transform" in NeWS 1.1 OK ?
Message-ID: <8901260111.AA23398@brillig.umd.edu>
Date: 26 Jan 89 01:12:27 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 23

The reason transform is giving unexpected results is that it takes
into account the height of the canvas you're on, flipping the
y-coordinate to pixrect "device" coordinates. The pixrect origin is
the upper left corner, while the default NeWS origin is the lower
left. This is a pain, and probably the reason why the matrix args to
transform, scale, etc, are not implemented. A transformation matrix
for one canvas will not work the same on a another canvas of a
different height, because there is this implicit transformation and y
scale flip. 

I've recently run into a bug with setting the /XLocation and
/YLocation fields of events. When I am on a canvas other than the
frame buffer, and I set them to some value, then immediatly read them
back, THEY'RE DIFFERENT!! To correctly set the event coordinates to a
position relative to my canvas, I have to setcanvas to the frame
buffer, manually subtract my canvas's offset from the lower left
corner of the framebuffer from my coordinates, and THEN def the
/XLocation and /YLocation fields.

I think my problem is also related to the pixrect origin -vs-
PostScript origin problem. Pixrects are *EVIL*.

	-Don