[gsharp-devel] Architecture question

[Robert Strandh]

I think I see more clearly now.  

It seems feasible for the score pane to define a bunch of presentation
types, such as this:

(define-presentation-type clef () :options (name x staff-step))

(define-presentation-method present (object
				     (type clef)
				     stream
				     (view score-view)
				     &key acceptably for-context-type)
  (declare (ignore acceptably for-context-type))
  (with-output-as-presentation (stream object 'clef)
    (draw-clef stream name x staff-step)))

(define-presentation-method present (object
				     (type clef)
				     stream
				     (view textual-view)
				     &key acceptably for-context-type)
  (declare (ignore acceptably for-context-type))
  (format stream "[~a clef on staff step ~a]" name staff-step))

and for client code to draw using calls such as this:

    (present (clef staff)
	     `((score-pane:clef)
	       :name ,(name (clef staff))
	       :x ,(+ x1 10)
	       :staff-step ,(lineno (clef staff)))
	     :stream pane)

It would also be nice to define a hierarchy of presentations.  For
instance, there might be a presentation type `staff' and the
presentation types like `clef' would accept an argument that indicates
to which staff the objects belong.  

Client code would look like this:


    (present 1 ((score-pane:system) :x 100 :y 100) :stream pane)
    (present mystaff
             `((score-pane:staff
	       :system 1
               :y 10 ;relative to the top of the system
               :type :fiveline))
             :stream pane)
    (present (clef staff)
             `((score-pane:clef)
	       :staff mystaff
               :name :bass
               :x 10 ; relative to the left edge of the staff
               :staff-step 6)
             :stream pane)

The score pane would compare client objects using (say) eql (so as to
allow for integers) and establish relationships
               
Question: would it be necessary for client code to sometimes just draw
things without presenting them?  I kind of think so.  It would then be
nice to be able to reuse the presentation types in a draw function as
opposed to the current system with draw-??? functions.  In that case,
could that be a different presentation generic function, which would
have the strange behavior of not creating presentations.  Or should it
just be a different view for present, say draw-view that has draws
without presenting:

    (present mystaff
             `((score-pane:staff
	       :system 1
               :y 10 ;relative to the top of the system
               :type :fiveline))
             :stream pane
             :view score-pane:draw-view)

Comments? 
-- 
Robert Strandh

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