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From: don@BRILLIG.UMD.EDU (Don Hopkins)
Newsgroups: comp.windows.news
Subject: Mouse event coordinates getting screwed up upon window resize
Message-ID: <8710160532.AA23176@brillig.umd.edu>
Date: Fri, 16-Oct-87 01:51:01 EDT
Article-I.D.: brillig.8710160532.AA23176
Posted: Fri Oct 16 01:51:01 1987
Date-Received: Sat, 17-Oct-87 18:33:09 EDT
Sender: usenet@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 39

I wrote a psh script that made a subclass of DefaultWindow, that
forked an event manager which would listen for mouse events on the
clientcanvas, and draw things at the coordinates of the events. Once I
resized the window, though, the coordinates of all the events would
all be off by some translation.

I finally got it to work right by making an instance variable:

  /ClientCanvasMatrix null def 

And overriding the /ShapeClientCanvas method:

  /ShapeClientCanvas { % - => - ([Re]set client canvas' shape) 
    /ShapeClientCanvas super send 
    gsave
      ClientCanvas setcanvas 
      ClientCanvasMatrix null eq { 
        /ClientCanvasMatrix matrix def 
      } if 
      ClientCanvasMatrix currentmatrix 
    grestore
  } def 

And inserting in the beginning of each function that handled an event:

    ClientCanvasMatrix setmatrix 

I think it has something to do with the fact that the process that is
reshaping the window (thus altering the CTM) is different that the one
doing the drawing. Isn't the CTM a part of the graphics state, which
is a part of the process, as opposed to the canvas?

Does anybody know what's really going on, and if there's a way to go
about things so that this is not a problem? (How about adding my
client's interests to the frame interests, so they are all handled by
the same process?) Should each window have a CTM (or a whole graphics
state) as an instance variable?

	-Don