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revision 1.108 by tjl, Fri Feb 14 19:30:21 2003 UTC revision 1.109 by tjl, Fri Feb 14 19:45:33 2003 UTC
# Line 374  the final positions of the buoys need be Line 374  the final positions of the buoys need be
374    
375    
376    
377  Paper  Unique background textures
378  -----  -------------------------
379    
380  The fragments of nodes seen in buoys are  The fragments of nodes shown in buoys are
381  generally very similar in appearance.  generally very similar in appearance.
382  The user could identify the related documents by  The user could identify the nodes by
383  reading the text of a fragment, but that requires attention.  reading the text of the fragment, but that requires too much attention.
384    
385  Using a unique background texture for each document changes the  Using a unique background texture for each node
386    ("virtually printing the node
387    on fancy paper") changes the
388  situation dramatically: the user can perceive the identity  situation dramatically: the user can perceive the identity
389  of the most familiar documents at a glance,  of the most familiar documents at a glance,
390  even when only fragments are shown.  even when only small fragments are shown.
391  Furthermore, when moving from node to node, the pre-attentive  Furthermore, when moving from node to node, the pre-attentive
392  cues of identity help the user maintain a sense of direction.  cues of identity help the user maintain a sense of direction.
393    
394  The background textures are randomly chosen using the identity as a seed.  The texture should not be
395  That is, each document has a unique backround texture, but the texture  in any way related to the contents of the document.
 is not in any way related to the contents of the document (except  
 that a hash of the contents could be used as an identity of an immutable  
 document).  
396  That way, the textures in any view are as different as possible,  That way, the textures in any view are as different as possible,
397  even if the documents are similar.  even if the documents are similar. [XXX Need to explain a LOT better]
398  Furthermore, the unique background of any document can be instantly drawn,  
399  as soon as the identity inside the system is known.  The background textures are generated at run time,
400    using the node identity as a seed value to a pseudo-random number
401  The distribution of the textures is designed to be maximally  generator. Because the algorithm is fixed, a node's texture
402  diverse and recognizable with respect to a rough, qualitative model  will remain the same between invocations even though the
403  of visual perception.  texture is not stored anywhere.
404    
405    The generation of usefully unique background textures
406    is not simple - the distribution has to be carefully
407    adjusted to produce
408    maximally
409    diverse and recognizable textures, taking into
410    account the properties of human visual perception.
411  For example, backgrounds with random pixels (noise) would all  For example, backgrounds with random pixels (noise) would all
412  look the same, because the pixels are not perceived individually.  look the same, because the pixels are not perceived individually.
413  However, shapes and overall colors should be independently random to  However, shapes and overall colors should be independently random to
# Line 419  but repeating with a randomly chosen *re Line 425  but repeating with a randomly chosen *re
425    
426  At each pixel, the combined values of the basis textures  At each pixel, the combined values of the basis textures
427  are used for interpolating between the colors  are used for interpolating between the colors
428  of a small, randomly chosen palette of *compatible* colors.  of a small palette of *compatible* colors, randomly
429    chosen from a carefully weighted distribution.
430  That way, the colors and shapes are independently random  That way, the colors and shapes are independently random
431  and the palette can be restricted to light colors to  and the palette can be restricted to light colors to
432  maintain readability.  maintain readability.

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