This file gives some information about the code in edit.c.  If you want to
change, add, or fix code, please read this text.  If you're not interested
in doing actual work on edit.c only C & D will be of interest to you.

A) basic policy
B) special functions
C) not implemented
D) known bugs

A) Basic Policy

The code has been made in such a way, that functions try to call other
(documented) functions if that is sufficient.  This might sometimes not be
the most efficient way, but it keeps the code clear.  This way I tried to keep
the number of functions that rely on the internal EDITSTATE structure as
low as possible.  For instance EDIT_WM_Cut() simply calls EDIT_WM_Copy() and
EDIT_WM_Clear().  The latter two are well documented message handlers, so
as long as they are right EDIT_WM_Cut() will never have to change again.

Example:
The best thing to do, when you want to know the offset of line 3, is calling
EDIT_EM_LineIndex().  Again this is a well documented message handler.  Don't
look at es->LineDefs[2].offset.  It would just be another reference to the
internal structure, and that would make it more difficult to change things.
Refer to EDIT_WM_???? and EDIT_EM_????? functions as much as possible.

The WND * pointer is used internally whenever possible.  Although it is not
the real HWND, it improves performance enough to use it.

All displaying is done by invalidating regions / rects.  Only
EDIT_EM_LineScroll() uses direct painting.  This way things become much
faster.  Although sometimes the response time might appear to be slow, it
would be much slower even, when everything would be painted instantly.  This
is especially true for scrollbar tracking and selection changes..



B) Special functions

The edit control needs to use local heap memory because applications may
rely on EM_GETHANDLE.  This is bad, but it can't be helped, we have to live
with that.  For this reason there is a nice EDIT_GetPointer() function,
which locks the heap buffer *only once*, no matter how often it is called.
Only at the end of the message handler EDIT_ReleasePointer() is called.  You
don't have to worry about unlocking the heap.  Calling EDIT_GetPointer() is
very fast if the buffer is already locked.
This way, the buffer gets locked / unlock only once every message, although
EDIT_GetPointer() may actually have been called a hundred times.
Only when the actual HLOCAL is needed (for example to ReAlloc), a call to
EDIT_ReleasePointer() is needed.  Look for instance in EDIT_MakeFit().

This brings us to EDIT_MakeFit().  It automatically re-allocates the buffer
if the size parameter > buffersize.  If everything is successful TRUE is
returned, otherwise FALSE.  Only when the buffer contents may grow you need
to call EDIT_MakeFit().  Currently this is only in EDIT_ReplaceSel() and
EDIT_WM_SetText().

EDIT_BuildLineDefs() is the most important function in edit.c.  It builds
the internal EDITSTATE structure.  As soon as text *might* have changed, or
when the appearance of the text on the screen *might* have changed, call
this function !  This includes changes of screen size, change of the font,
clipboard actions, etc. etc.  Most other functions that rely on EDITSTATE,
rely on the stuff this function builds.



C) Not Implemented

- ES_PASSWORD
- ES_CENTER
- ES_RIGHT
- EM_SETRECT
- EM_SETRECTNP
- EM_FMTLINES
- ES_AUTOVSCROLL (every multi line *is* auto vscroll)
- ES_AUTOHSCROLL (multi line can be yes or no, but single line only yes)
- WM_UNDO (=EM_UNDO)
- EM_CANUNDO
- EM_SCROLL (scrolling works, but this appears to be an undocumented message)
- ES_LOWERCASE
- ES_UPPERCASE
- ES_OEMCONVERT
- ES_WANTRETURN
- probably much, MUCH more

I encountered several undocumented messages, or message parameters.
EditWndProc() reports any unknown message with an id > WM_USER.



D) Known bugs.

-	Scrolling is weird, sometimes.  The current code makes the scrollbar
	of Notepad work, but the scrollbar code itself is broken.  Currently
	the scroll code of edit.c is *not* according to specs.  Instead, it
	is according to the broken scrollbar code.  If that gets fixed, this
	should be fixed, too.
-	The clipboard is broken.  Whenever things go wrong with
	cut/copy/paste, it is probably the clipboard that messes up things,
	not edit.c.
-	Turning on WordWrap with Notepad leaves part of the horizontal
	scrollbar visible (problem with WM_ERASEBKGND ???).


I am still very actively changing things.  Especially I am working
on Undo capabilities.  If you want to do things, other than bug fixes,
please mail me so we can synchronize.

Frans van Dorsselaer
dorssel@rulhm1.LeidenUniv.nl