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Re: Semantics of flipping inks From: "William M. York" <york@parc.xerox.com> Date: Mon, 25 Apr 1994 15:02:08 PDT

      Date:	Sat, 23 Apr 1994 13:13:56 -0700
      From:	Lawrence.G.Mayka@att.com

      I'm having some difficulty with the semantics of flipping inks.  The
      documentation is clear, for example, as to what CLIM:+FLIPPING-INK+
      does to output whose color happens to exactly match either
      CLIM:+FOREGROUND-INK+ or CLIM:+BACKGROUND-INK+.  But what does it do
      to any other color?  Are the consequences entirely unspecified?  

   Lifting the covers a little, you will find that flipping ink is
   nothing more than an interface to the tried-and-true raster graphics
   technique of XORing pixels together.  On the typical 8-bit
   pseudo-color display you find on many computers, CLIM can hack the
   bits such that any two specified colors get swapped when the XOR
   happens, and due to the nature of XOR, they will get swapped back if
   you do the operation again.  While you can't determine
   This kind of XOR-based highlighting is so
   useful that we thought we had to provide some kind of access to it in
   the CLIM graphics model.
	...
   So all the other colors on the screen get arbitrarily re-assigned.

Is this the same technique used by window managers (e.g., the Open
Look Virtual Window Manager that I use) for rubberbanding the window
outline when one moves or resizes a window?


        Lawrence G. Mayka
        AT&T Bell Laboratories
        lgm@ieain.att.com

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