Minimum Profit internals
========================

 Angel Ortega <angel@triptico.com>

This document describes some internal details of the mp implementation.

The drawing process
-------------------

(This section documents the drawing process as of version 4.99.3).

To ease the application of regular expressions to the on-screen part of a
document, a rather complicated process is done. The document is stored in
memory as a simple MPDM array of scalars, one for each line.

                         -----------------
                         ! First line    !
                         -----------------
 first line on screen -> ! Second line   !
                         -----------------
                         ! Third line    !
                         -----------------
                         ! ...           !
                         -----------------
 last line on screen --> ! Nth line      !
                         -----------------
                         ! Rest of doc.  |
                         -----------------

Or, as MPSL code,

 doc.txt.lines = [
     "First line",
     "Second line",
     "Third line",
     "...",
     "Nth line",
     "Rest of doc."
 ];

This way, normal text editing operations are very simple. But applying
regular expressions to these structures is impossible; to do that, the
visible part of the document (plus some lines above the first visible
one) is 'flattened' to a simple memory block. This is done by the
drw_prepare() function.

                     ------------------------------------------
 string buffer ->    !Second line\nThird line\n...\nNth line\n!
                     ------------------------------------------
 
                     ------------------------------------------
 attribute buffer -> !0000000000000000000000000000000000000000!
 (0: "normal")       ------------------------------------------

This flattened memory block is really two: one holding the characters
(including carriage returns to separate the lines) and another holding the
attributes, that will be reset to the 'normal' attribute.

After this conversion (a slightly modified join), all syntax highlight
regular expressions are matched to the character buffer, but filled in the
attribute buffer. The different regular expressions are applied by the
drw_words(), drw_multiline_regex(), drw_blocks(), drw_selection() and
the drw_matching_paren() functions.

                     ------------------------------------------
 string buffer ->    !Second line\nThird line\n...\nNth line\n!
 (unchanged)         ------------------------------------------
 
                     ------------------------------------------
 attribute buffer -> !1111110000000444440000000000005550000000!
                     ------------------------------------------

Once all attributes are applied to the text, a process is invoked that
converts the flat buffer back to an MPDM array where each element is itself
an array (for each line of text) of attribute / string pairs, done by the
mp_draw() function. This way drivers are very simplified and need only to
iterate the main array and draw each pair of attribute / string sequentially.

                         --- -------- --- ---------
 first line on screen -> !1! !Second! !0! ! line\n!
                         --- -------- --- ---------
                         --- ------- --- ---------
                         !4! !Third! !0! ! line\n!
                         --- ------- --- ---------
                         --- -------
                         !0! !...\n!
                         --- -------
                         --- ----- --- ---------
 last line on screen --> !5! !Nth! !0! ! line\n!
                         --- ----- --- ---------

Or, as MPSL code,

 info = [
        [ 1, "Second", 0, " line\n" ],
        [ 4, "Third", 0, " line\n" ],
        [ 0, "...\n" ],
        [ 5, "Nth", 0, " line\n" ]
 ];

----
Angel Ortega <angel@triptico.com> - $Date$
