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Re: Questions on glyph matrices used for rendering frame in terminal

From: Akib Azmain Turja
Subject: Re: Questions on glyph matrices used for rendering frame in terminal
Date: Tue, 05 Jul 2022 10:26:29 +0600

Gerd Möllmann <gerd.moellmann@gmail.com> writes:

>> 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?

Oh sorry, I meant "it will end up being equal to

>> --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?

The documentation says that something will happen, but I don't know
since I have never tried to do that.

>> 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.

I can't understand.  What does that glyph memory contain?  Individual
glyphs or the glyph matrix?  If the glyph memory holds the glyph matrix,
then IIUC glyph row is a row of that glyph matrix, so why clearing that
doesn't affect the glyph matrix?

>> 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.)

No, I'm not saying to rewrite, just wanted to know.


Akib Azmain Turja

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