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authorBehdad Esfahbod <behdad@gnome.org>2007-05-24 20:17:05 +0000
committerBehdad Esfahbod <behdad@src.gnome.org>2007-05-24 20:17:05 +0000
commit4bf96efe5913ead12b9a782d8eecbfcfde26e1b1 (patch)
tree6d770a00171232e09ced03118672948620a936eb /docs
parent48c98597fb8bc2b779500670d20486855681b202 (diff)
downloadpango-4bf96efe5913ead12b9a782d8eecbfcfde26e1b1.tar.gz
Document how Pango's vertical text support works.
2007-05-24 Behdad Esfahbod <behdad@gnome.org> * docs/tmpl/vertical.sgml: Document how Pango's vertical text support works. svn path=/trunk/; revision=2318
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@@ -9,6 +9,21 @@ Laying text out in vertical directions
Since 1.16, Pango is able to correctly lay vertical text out. In fact, it can
set layouts of mixed vertical and non-vertical text. This section describes
the types used for setting vertical text parameters.
+
+The way this is implemented is through the concept of
+<firstterm>gravity</firstterm>. Gravity of normal Latin text is south. A
+gravity value of east means that glyphs will be rotated ninety degrees
+counterclockwise. So, to render vertical text one needs to set the gravity
+and rotate the layout using the matrix machinery already in place. This has
+the huge advantage that most algorithms working on a #PangoLayout do not need
+any change as the assumption that lines run in the X direction and stack in
+the Y direction holds even for vertical text layouts.
+
+Applications should only need to set base gravity on #PangoContext in use, and
+let Pango decide the gravity assigned to each run of text. This automatically
+handles text with mixed scripts. A very common use is to set the context base
+gravity to auto and rotate the layout normally. Pango will make sure that
+Asian languages take the right form, while other scripts are rotated normally.
</para>
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