Re: emacs rendering comparisson between emacs23 and emacs26.3

[Eli Zaretskii]

> Cc: address@hidden, address@hidden, address@hidden, address@hidden
> From: martin rudalics <address@hidden>
> Date: Wed, 8 Apr 2020 10:37:46 +0200
> 
>  > It stops when it gets to a buffer position where the
>  > 'fontified' text property changes its value.  If the new value of
>  > 'fontified' is nil, the display engine calls fontification-functions.
>  > jit-lock adds its function to that hook, so jit-lock is called.  What
>  > jit-lock does, in a nutshell, is call the current buffer's
>  > fontification function(s) on a chunk of text starting at the position
>  > for which it was called, and it puts on that chunk a value of t for
>  > the 'fontified' text property.  (Where that chunk ended is the
>  > position where the 'fontified' property's value will again change to
>  > nil, and if that position is inside the window, jit-lock will be
>  > called again when the display engine gets to that position.)  After
>  > fontification-functions return, the display engine processes the faces
>  > in the chunk that has been fontified; then it continues marching
>  > through the buffer.
> 
> IIRC fontification can also modify text before the position where the
> 'fontified' property changed to nil.  Or is that wrong?

What is actually fontified depends on the buffer's
fontification-functions; jit-lock just calls those functions with a
region that starts at the first position in the window that has its
'fontified' property nil, and ends jit-lock-chunk-size (500 bytes by
default) after that.  However, the 'fontified' property will be set by
jit-lock to t only for text in that chunk, as jit-lock has no way of
knowing what was actually fontified.