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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 15:03:23 +0600

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

>> On 2022-07-05,, at 6:26 , Akib Azmain Turja <akib@disroot.org> wrote:
>> Gerd Möllmann <gerd.moellmann@gmail.com <mailto: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
>> *frame_matrix->matrix_w*".
> Probably.  I don't remember what I thought exactly when I wrote that code.  
> But, a few lines above what you mentioned there is
>       /* Fill up the frame row with spaces up to the left margin of the
>        window row.  */
>       fill_up_frame_row_with_spaces (frame_row, window_matrix->matrix_x);
> In general, I prefer code that relies on what is known locally, instead of 
> what is known more globally, so to speak.  (We have too much of that already 
> in Emacs.)  Maybe that was the reason.
> In this case, because of the fill_up..., we know locally that the frame row 
> is filled up to matrix_x of the window, so...
>>> 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?
> It does affect a struct glyph_matrix, indirectly, because a struct glyph_row 
> used by it is memset to zeros.
> But no struct glyph is modified by that.  Please take a look at 
> clear_glyph_row.  Only bookkeeping information is cleared. The struct 
> glyph_row points to struct glyphs, but the glyphs themselves are not changed.
> Have you read dispextern.h?  There are some comments that might be helpful.

Now I get it.  Thanks.

Akib Azmain Turja

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