[Gzz-commits] manuscripts/xupdf article.rst

[Tuomas J. Lukka]

CVSROOT:        /cvsroot/gzz
Module name:    manuscripts
Changes by:     Tuomas J. Lukka <address@hidden>        03/02/14 14:45:34

Modified files:
        xupdf          : article.rst 

Log message:
        libpaper

CVSWeb URLs:
http://savannah.gnu.org/cgi-bin/viewcvs/gzz/manuscripts/xupdf/article.rst.diff?tr1=1.108&tr2=1.109&r1=text&r2=text

Patches:
Index: manuscripts/xupdf/article.rst
diff -u manuscripts/xupdf/article.rst:1.108 manuscripts/xupdf/article.rst:1.109
--- manuscripts/xupdf/article.rst:1.108 Fri Feb 14 14:30:21 2003
+++ manuscripts/xupdf/article.rst       Fri Feb 14 14:45:33 2003
@@ -374,34 +374,40 @@
 
 
 
-Paper
------
+Unique background textures
+-------------------------
 
-The fragments of nodes seen in buoys are 
+The fragments of nodes shown in buoys are 
 generally very similar in appearance.
-The user could identify the related documents by
-reading the text of a fragment, but that requires attention.
+The user could identify the nodes by
+reading the text of the fragment, but that requires too much attention.
 
-Using a unique background texture for each document changes the 
+Using a unique background texture for each node 
+("virtually printing the node
+on fancy paper") changes the 
 situation dramatically: the user can perceive the identity
 of the most familiar documents at a glance, 
-even when only fragments are shown.
+even when only small fragments are shown.
 Furthermore, when moving from node to node, the pre-attentive
 cues of identity help the user maintain a sense of direction.
 
-The background textures are randomly chosen using the identity as a seed. 
-That is, each document has a unique backround texture, but the texture 
-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).
+The texture should not be
+in any way related to the contents of the document.
 That way, the textures in any view are as different as possible,
-even if the documents are similar.
-Furthermore, the unique background of any document can be instantly drawn,
-as soon as the identity inside the system is known.
-
-The distribution of the textures is designed to be maximally 
-diverse and recognizable with respect to a rough, qualitative model 
-of visual perception.
+even if the documents are similar. [XXX Need to explain a LOT better]
+
+The background textures are generated at run time,
+using the node identity as a seed value to a pseudo-random number
+generator. Because the algorithm is fixed, a node's texture
+will remain the same between invocations even though the
+texture is not stored anywhere.
+
+The generation of usefully unique background textures
+is not simple - the distribution has to be carefully
+adjusted to produce
+maximally 
+diverse and recognizable textures, taking into 
+account the properties of human visual perception.
 For example, backgrounds with random pixels (noise) would all
 look the same, because the pixels are not perceived individually.
 However, shapes and overall colors should be independently random to 
@@ -419,7 +425,8 @@
 
 At each pixel, the combined values of the basis textures 
 are used for interpolating between the colors
-of a small, randomly chosen palette of *compatible* colors. 
+of a small palette of *compatible* colors, randomly
+chosen from a carefully weighted distribution. 
 That way, the colors and shapes are independently random 
 and the palette can be restricted to light colors to 
 maintain readability.