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Re: Questions on glyph matrices used for rendering frame in terminal
From: |
Gerd Möllmann |
Subject: |
Re: Questions on glyph matrices used for rendering frame in terminal |
Date: |
Mon, 4 Jul 2022 21:37:02 +0200 |
>>
> 1. What's the purpose of the following in
> build_frame_matrix_from_leaf_window? "frame_row->used[TEXT_AREA]" will
> always end up being equal to "window_matrix->matrix_w" after processing
> the right-most window of the row.
I don't understand. What about the /matrix_x/ + matrix_w below?
>
> --8<---------------cut here---------------start------------->8---
> /* Set number of used glyphs in the frame matrix. Since we fill
> up with spaces, and visit leaf windows from left to right it
> can be done simply. */
> frame_row->used[TEXT_AREA]
> = window_matrix->matrix_x + window_matrix->matrix_w;
> --8<---------------cut here---------------end--------------->8---
>
>
> 2. From the documentation of make-terminal-frame:
>
> > Note that changing the size of one terminal frame automatically
> > affects all frames on the same terminal device.
>
>
> But why? Do they share glyph matrices, since only one of them is
> visible at a single time?
How else should other frames behave? Leave a "hole" on the terminal where
nothing is displayed when the TTY window is made larger? And what if the
terminal is made smaller?
>
>
> 3. Why clear the desired matrix in build_frame_matrix? As I understand,
> that would clear the glyph matrices of windows the frame, because window
> desired matrix shares memory with frame desired matrix, and its seems
> like build_frame_matrix is called after window desired matrices are
> built.
>
> --8<---------------cut here---------------start------------->8---
> /* Clear all rows in the frame matrix covered by window matrices.
> Menu bar lines are not covered by windows. */
> for (i = FRAME_TOP_MARGIN (f); i < f->desired_matrix->nrows; ++i)
> clear_glyph_row (MATRIX_ROW (f->desired_matrix, i));
> --8<---------------cut here---------------end--------------->8---
In the TTY case, the glyph memory (struct glyph) for desired window matrices is
sub-allocated from the glyph memory that is allocated for the frame. The
glyph_row structures on the other hand are different between windows and frame.
Clear_glyph_row doesn't affect the glyph memory, only the glyh_rows.
>
>
> 4. And one more question: why don't Emacs is use the window feature of
> ncurses despite depending on it? Is it inefficient or lack of any
> feature?
>
The reasons I can think of are
- ncurses is considerably younger than Emacs
- Its predecessor 'curses' (from BSD, IIRC) wasn't available everywhere (think
VMS, MS-DOS, maybe others), when that part of the code was written. I would
guess that might have been around 1985. What would that be - Emacs 16 :-).
Maybe there are also other technical reasons that make a rewrite with ncurses
impossible, I don'T know.
(And there's of course always the consideration of why rewrite something that
works.)
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