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* etc/TODO (redisplay): Add an item for making redisplay cycle
more scalable when there are many frames.
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Eli Zaretskii 2020-12-17 16:22:05 +02:00
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@ -536,6 +536,42 @@ This should go with point, so that motion commands can also move
through tall images. This value would be to point as window-vscroll through tall images. This value would be to point as window-vscroll
is to window-start. is to window-start.
** Make redisplay smarter about which parts to redraw
Currently, redisplay has only 2 levels of redrawing: either it
redisplays only the selected window on the selected frame, or it
redisplays all the windows on all the frames. This doesn't scale well
when the number of visible frames is large.
Currently, two variables are used to make the decision what to
redisplay: update_mode_lines and windows_or_buffers_changed. These
are set by various functions called from Lisp, and if redisplay finds
one of them to be non-zero, it considers all the windows on all the
frames for redisplay.
The idea is to make the decision which parts need to be redrawn more
fine-grained. Instead of simple boolean variables, we could have a
bitmapped variable which records the kinds of changes done by Lisp
since the previous redisplay cycle. Then the decision what exactly
needs to be redrawn could be made based on the bits that are set.
For example, one reason to consider all frames is that some scrolling
command sets the update_mode_lines variable non-zero. This is done
because the frame title, which doesn't belong to any window, needs to
be reconsidered when the selected window is scrolled. But considering
the frame title doesn't have to redisplay all the other windows on the
frame, doesn't need to recompute the menu items and the tool-bar
buttons, and doesn't need to consider frames other than the selected
one. Being selective about what parts of the Emacs display need to be
reconsidered and redrawn given the changes since the last redisplay
will go along way towards making redisplay more scalable.
One way of making this change is to go through all the places that set
update_mode_lines and windows_or_buffers_changed, figure out which
portions of the Emacs display could be affected by each change, and
then implement the bitmap which will record each of these affected
display portions. The logic in redisplay_internal will then need to
be restructured so as to support this fine-grained redisplay.
** Address internationalization of symbols names ** Address internationalization of symbols names
Essentially as if they were documentation, e.g. in command names and Essentially as if they were documentation, e.g. in command names and
Custom. Custom.