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backends/native: Handle triple resolution mouse wheels better

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When a remote desktop user emits a virtual smooth scrolling event, a
smooth scroll event, that is not emulated, is emitted and on occasion
a discrete scroll event, that is emulated, is emitted.
As base for the discrete scrolling event, the smooth scrolling steps
are accumulated.
When the accumulated smooth scrolling steps surpass the
DISCRETE_SCROLL_STEP, the discrete scrolling event is emitted.

Currently, mutter uses for DISCRETE_SCROLL_STEP the value 10, which is
a terrible value to work with, especially for high resolution mouse
wheels.
When a triple resolution mouse wheel is used, each scrolling step will
have the value 3 1/3.
Three of such events won't however surpass the DISCRETE_SCROLL_STEP.

To fix this situation, add DBL_EPSILON to the calculation step, when
checking for the discrete scroll event to ensure that 3 smooth scroll
events, with each having the value 3 1/3, emit a discrete scrolling
event.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1727>
This commit is contained in:
Pascal Nowack 2021-02-11 12:33:26 +01:00
parent a5d692582d
commit c77e943ce2
1 changed files with 4 additions and 2 deletions
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6
src/backends/native/meta-seat-impl.c
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@ -818,8 +818,10 @@ check_notify_discrete_scroll (MetaSeatImpl *seat_impl,
{ {
int i, n_xscrolls, n_yscrolls; int i, n_xscrolls, n_yscrolls;
n_xscrolls = floor (fabs (seat_impl->accum_scroll_dx) / DISCRETE_SCROLL_STEP); n_xscrolls = floor ((fabs (seat_impl->accum_scroll_dx) + DBL_EPSILON) /
n_yscrolls = floor (fabs (seat_impl->accum_scroll_dy) / DISCRETE_SCROLL_STEP); DISCRETE_SCROLL_STEP);
n_yscrolls = floor ((fabs (seat_impl->accum_scroll_dy) + DBL_EPSILON) /
DISCRETE_SCROLL_STEP);
for (i = 0; i < n_xscrolls; i++) for (i = 0; i < n_xscrolls; i++)
{ {