# 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> - `$Date`$