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revision 1.104 by tjl, Fri Feb 14 16:35:17 2003 UTC revision 1.105 by tjl, Fri Feb 14 16:56:59 2003 UTC
# Line 261  fisheye. Line 261  fisheye.
261  Buoy placement  Buoy placement
262  --------------  --------------
263    
264  Usually everything is either in the coordinate system of the  In most current systems,
265    all graphical objects are placed
266    in either the coordinate system of the
267  virtual paper (e.g., the margins of the web page being scrolled)  virtual paper (e.g., the margins of the web page being scrolled)
268  or in the outside coordinate system, independent of the page.  or the external coordinate system, independent of the page.
269  This is originally because of performance: it is most efficient to update  This is originally because of performance: it is most efficient to update
270  a single, rectangular (or rectangular, rectangularly obscured) area  a single, rectangular (or rectangular, rectangularly obscured) area
271  of screen.  of screen.
272  With fast hardware, there is no need to be limited to rectangular sections  For the same reason, smooth scaling is only seldom used.
 because the whole screen can always be drawn.  
 Thus, it is possible to place objects in different, interconnected  
 coordinate systems.  
273    
274  What we call *buoy* is a common idea from technical diagrams:  With modern graphics hardware, there is no need to be limited to rectangular sections
275  draw a line to the relevant point and place the label in the margin  and discrete scales
276  (see Fig. [ref-fignasa]_).  because the whole screen can be redrawn at interactive frame rates.
277  The scale and location of the buoy and the document can be  Thus, it is possible to place objects in different
278  smoothly adjusted, independent of each other, with the connection  coordinate systems whose motion depends on the others in complex ways.
 line cross-cutting the view.  
279    
280  We use buoys as link targets floating around the focus.  We use buoys as link targets floating around the focus.
281  For the layout of the buoys, several desirable layout constraints  What we call *buoy* is a commonly used tool in technical diagrams:
282  can be enumerated:  placing a label at the edge of the image and connecting the label
283    to the relevant location (anchor) by a line
284    (see Fig. [ref-fignasa]_).
285    
286  - buoys should not be placed directly on the focus  For the layout of the buoys we give the following criteria
287  - buoys should be placed close to their anchors  (in order of importance):
288  - buoys anchored closer to the focus should be larger  
289    - buoys should not be placed directly on the focus (center of screen)
290    - buoys whose anchors are close to the focus should be large
291  - the view should animate continuously when the focus moves  - the view should animate continuously when the focus moves
292  - the user should be able to understand and predict the motion  - the user should be able to understand and predict the motion
293    of the buoys.    of the buoys.
294    - buoys should be placed close to their anchors
295    
296  Furthermore,  Furthermore,
297  it is important to maintain orientation locally,  it is important to maintain orientation locally,

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