GitHub #233, documenting style buffers and utf8.

src/Fl_Text_Display.cxx

@@ -1,5 +1,5 @@
 //
-// Copyright 2001-2020 by Bill Spitzak and others.
+// Copyright 2001-2021 by Bill Spitzak and others.
 // Original code Copyright Mark Edel.  Permission to distribute under
 // the LGPL for the FLTK library granted by Mark Edel.
 //
@@ -394,6 +394,17 @@ void Fl_Text_Display::buffer( Fl_Text_Buffer *buf ) {
 
  Styles are ranged from 65 ('A') to 126.
  
+ \note Style information in the style buffer must have the same byte offset as
+ the corresponding character in the text buffer. UTF-8 characters can have a 
+ length of four, in some cases even six bytes. Style information must take 
+ this into account and fill the unused bytes with 0. See `fl_utf8len()`.
+ 
+ Text: "*g* r ü *n*" , where normal style is 'A', and bold is 'B'
+ \code
+ Text Buffer(hex):  67 72 c3 bc 6e : gr..n
+ Style Buffer(hex): 42 41 41 00 42 : BAA.B
+ \endcode
+ 
  \param styleBuffer this buffer works in parallel to the text buffer. For every
    character in the text buffer, the style buffer has a byte at the same offset
    that contains an index into an array of possible styles.