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erasing presentations

        I'm working with Genera 7.2 and have been having trouble with using
        presentations.  We've been working with them for over 6 months and have
        achieved a lot of remarkable things, but our conclusion is that we still
        don't *really* know how to use them.  I'm wondering if this is a common
        perception, or if we are just slow.
        	I'm also wondering why Symbolics doesn't seem to allow for
        creating derived flavors of presentations.  It is possible to do
        (defflavor 1my-graphic-presentation
0              (my-slot)
        but then there isn't any mechanism for getting the things made by the
        system.  That is, the macros 
        don't allow you to specify the flavor of presentation that is created.
        It seems to me intuitive that such a thing would be valuable and that
        the existence of the two different macros proves it.  Of course, I could
        probably have done what I wanted to do if I had hacked the source (note
        that this is source that Symbolics does not ordinarily distribute), but
        I wanted to work within the system, especially considering that I'm not
        sure about how the system is supposed to be used.  There are probably
        other techniques, using the (undocumented) function
        dw:displayed-presentation-add-inferior and related functions.


I have a flavor called screen-point that I specify when presented in the
following manner:
(graphics:with-output-as-graphics-presentation (screen :type 'screen-point
								     :object self)
	    (graphics:draw-circle x y 5
				    :stream screen))
        A particular example for why I might want to do this is to create a
        class of presentations with paths that connect them to other
        presentations, such that the endpoints can be moved around while visual
        connections are maintained.  Also, I'd like to animate presentations by
        changing visual features (such as position, shape, inferior
        presentations) as the underlying objects change properties.  It could be
        that my conception of the partitioning between objects and presentations
        is brain dead.
        I've been assuming that some of my trouble is associated with the
        relative immaturity of dynamic windows and presentations, and that the
        documentation and code is likely to improve in the next release.
        Unfortunately, that will probably be too late for us.
        Any clues or comments?
          -- Paul Vaughan
In general I think the software is there that you want, you just have to
play with the presentation software A LOT.  What is missing is CLEAR
DOCUMENTATION with MANY examples.  I had to work very hard to determine
what was going on with the scantily documented parts of presentation
and dw:define-program-framework software.