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fix(ui): delay win_viewport until screen update #24182

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Problem:
Sometimes, when nvim sends the `win_viewport` event, for example when scrolling
with visible folds on the screen, it reports the `scroll_delta` value one batch
into "future". So when the client application is trying to show the new viewport
it's not yet updated, resulting in temporary corruption / screen flickering.

For more details see #23609, and starting from [this comment](
https://github.com/neovide/neovide/pull/1790#issuecomment-1518697747) in
https://github.com/neovide/neovide/pull/1790,, where the issue was first
detected. Note that some of the conclusions in those are not fully accurate, but
the general observations are.

Solution:
When there are pending updates to a Window, delay the `win_viewport` UI event
until the updates are sent. This ensures that there's no flush between sending
the viewport and updating of the lines corresponding to the new viewport.

Document the existing viewport behaviour (for cases where there are no
extra flushes), give a hint about how applications can deal with the slightly
surprising behaviour of the viewport event being sent after the updates.

Fixes https://github.com/neovim/neovim/issues/23609
This commit is contained in:
fredizzimo 2023-07-05 16:31:34 +03:00 committed by GitHub
parent 8a788e2daa
commit 1de82e16c1
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3 changed files with 10 additions and 2 deletions
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7
runtime/doc/ui.txt
View File

@ -643,6 +643,13 @@ tabs.
only count as one line. When scrolling more than a full screen it is
an approximate value.
All updates, such as `grid_line`, in a batch affects the new viewport,
despite the fact that `win_viewport` is received after the updates.
Applications implementing, for example, smooth scrolling should take
this into account and keep the grid separated from what's displayed on
the screen and copy it to the viewport destination once `win_viewport`
is received.
["win_extmark", grid, win, ns_id, mark_id, row, col] ~
Updates the position of an extmark which is currently visible in a
window. Only emitted if the mark has the `ui_watched` attribute.

4
src/nvim/window.c
View File

@ -1029,7 +1029,9 @@ void ui_ext_win_position(win_T *wp, bool validate)
void ui_ext_win_viewport(win_T *wp)
{
if ((wp == curwin || ui_has(kUIMultigrid)) && wp->w_viewport_invalid) {
// NOTE: The win_viewport command is delayed until the next flush when there are pending updates.
// This ensures that the updates and the viewport are sent together.
if ((wp == curwin || ui_has(kUIMultigrid)) && wp->w_viewport_invalid && wp->w_redr_type == 0) {
const linenr_T line_count = wp->w_buffer->b_ml.ml_line_count;
// Avoid ml_get errors when producing "scroll_delta".
const linenr_T cur_topline = MIN(wp->w_topline, line_count);

1
test/functional/ui/multigrid_spec.lua
View File

@ -3808,7 +3808,6 @@ describe('ext_multigrid', function()
]], win_viewport={
[2] = {win = {id = 1000}, topline = 30586, botline = 30592, curline = 30591, curcol = 0, linecount = 30592, sum_scroll_delta = 30588};
}}
command('autocmd CursorMoved * ++once call line("w$")') -- FIXME: this should not be needed
feed('gg')
screen:expect{grid=[[
## grid 1