CLIM mail archive


Semantics of flipping inks From: "William M. York" <> Date: Mon, 25 Apr 1994 15:02:08 PDT

   Date: Thu, 28 Apr 94 14:19:25 CDT

	 Date:	Sat, 23 Apr 1994 13:13:56 -0700

	 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?

Yes, usually.


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