Re: Truncating scroll runs that copy to where we copied to

[YAMAMOTO Mitsuharu]

>>>>> On Tue, 22 Nov 2011 01:04:45 -0500, Eli Zaretskii <address@hidden> said:

> You can help if you explain in more detail what is wrong with the
> current code.  That is what I need to assess the correctness of the
> patch.  I hoped that Yamamoto-san would do that.  Failing that, I'll
> need to figure it out myself, which will take more time, and thus
> will have to wait a couple of days until I have that time to sit
> down and look into this.  I do intend to do that, make no mistake.

Actually, I told what was wrong with the current code in my first
post:

>>>>> On Sun, 20 Nov 2011 16:13:59 +0900, YAMAMOTO Mitsuharu <address@hidden> 
>>>>> said:

> I think that `scrolling_window' needs to truncate scroll runs that
> copy to where we copied to; otherwise, `assign_row (to, from)'
> assigns a previously disabled bogus row in the desired matrix when
> we have an overlap in the copy destination.

        /* Assign matrix rows.  */
        for (j = 0; j < r->nrows; ++j)
          {
            struct glyph_row *from, *to;
            int to_overlapped_p;

            to = MATRIX_ROW (current_matrix, r->desired_vpos + j);
            from = MATRIX_ROW (desired_matrix, r->desired_vpos + j);
            to_overlapped_p = to->overlapped_p;
            from->redraw_fringe_bitmaps_p = from->fringe_bitmap_periodic_p;
            assign_row (to, from);
            to->enabled_p = 1, from->enabled_p = 0;
            to->overlapped_p = to_overlapped_p;
          }

If there's an overlap (I don't mean the variable to_overlapped_p) in
the copy destinations of two runs, then `from' row in the desired
matrix becomes a bogus one that had been in the current matrix after
processing the first run (because assign_row actually does swap), and
that row is disabled by `from->enabled_p = 0'.  So, when processing
the second run, the `from' row is now the previously disabled bogus
row and it is assigned to a row in the current matrix.

                                     YAMAMOTO Mitsuharu
                                address@hidden