added a howto for adding a new encoding to wxWin

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@26454 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/tech/index.txt

@@ -18,6 +18,7 @@ tn0014.txt   XRC resources format specification
 tn0015.txt   How to add new bitmaps to wxWindows UI elements
 tn0016.txt   How to add new files and libraries to wxWindows build system (Bakefile)
 tn0017.txt   How to write unit tests for wxWindows classes
+tn0018.txt   How to add a new font encoding/charset to wxWindows?
 
 
 Version: $Id$

docs/tech/tn0018.txt

@@ -0,0 +1,68 @@
+                 How to add a new font encoding to wxWindows
+                 ===========================================
+
+I. Introduction
+---------------
+
+ wxWindows has built in support for a certain number of font encodings (which
+is synonymous with code sets and character sets for us here even though it is
+not exactly the same thing), look at include/wx/fontenc.h for the full list.
+This list is far from being exhaustive though and if you have enough knowledge
+about an encoding to add support for it to wxWindows, this tech note is for
+you!
+
+ A word of warning though: this is written out of my head and is surely
+incomplete. Please correct the text here, especially if you detect problems
+when you try following it.
+
+ Also note that I completely ignore all the difficult issues of support for
+non European languages in the GUI (i.e. BiDi and text orientation support).
+
+
+II. The receipt
+---------------
+
+Suppose you want to add support for Klingon to wxWindows. This is what you'd
+have to do:
+
+1. include/wx/fontenc.h: add a new wxFONTENCODING_KLINGON enum element, if
+   possible without changing the values of the existing elements of the enum
+   and be careful to now make it equal to some other elements -- this means
+   that you have to put it before wxFONTENCODING_MAX
+
+2. wxFONTENCODING_MAX must be the same as the number of elements in 3
+   (hopefully) self explanatory arrays in src/common/fmapbase.cpp:
+   a) gs_encodings
+   b) gs_encodingDescs
+   c) gs_encodingNames
+
+   You must update all of them, e.g. you'd add wxFONTENCODING_KLINGON,
+   "Klingon (Star Trek)" and "klingon" to them in this example. The latter
+   name should ideally be understandable to both Win32 and iconv as it is used
+   to convert to/from this encoding under Windows and Unix respectively.
+   Typically any reasonable name will be supported by iconv, if unsure run
+   "iconv -l" on your favourite Unix system. For the list of charsets
+   supported under Win32, look under HKEY_CLASSES_ROOT\MIME\Database\Charset
+   in regedit. Of course, being consistent with the existing encoding names
+   wouldn't hurt neither.
+
+3. Normally you don't have to do anything else if you've got support for this
+   encoding under both Win32 and Unix. If you haven't, you should modify
+   wxEncodingConverter to support it (this could be useful anyhow as a
+   fallback for systems where iconv is unavailable). To do it you must:
+   a) add a new table to src/common/unictabl.inc: note that this file is auto
+      generated so you have to modify misc/unictabl script instead (probably)
+   b) possibly update EquivalentEncodings table in src/common/encconv.cpp
+      if wxFONTENCODING_KLINGON can be converted into another one
+      (losslessly only or not?)
+
+4. Add a unit test (see tn0017.txt) for support of your new encoding (with
+   time we should have a wxCSConv unit test so you would just add a case to
+   it for wxFONTENCODING_KLINGON) and test everything on as many different
+   platforms as you can.
+
+
+=== EOF ===
+
+Author:  VZ
+Version: $Id$