Add `ns-scroll-event-delta-factor'

* src/nsterm.m (- mouseDown): Take delta factor into account.
(Vns_scroll_event_delta_factor): New variable.

* lisp/cus-start.el: Add option.

1 files changed, 12 insertions, 0 deletions

diff --git a/src/nsterm.m b/src/nsterm.m
index 78bbae69a27..f5c2d4d9fbc 100644
--- a/src/nsterm.m
+++ b/src/nsterm.m
@@ -6665,6 +6665,12 @@ not_in_argv (NSString *arg)
           if (lines == 0 && x_coalesce_scroll_events)
             return;
 
+          if (NUMBERP (Vns_scroll_event_delta_factor))
+            {
+              x *= XFLOATINT (Vns_scroll_event_delta_factor);
+              y *= XFLOATINT (Vns_scroll_event_delta_factor);
+            }
+
           emacs_event->kind = horizontal ? HORIZ_WHEEL_EVENT : WHEEL_EVENT;
           emacs_event->arg = list3 (make_fixnum (lines),
                                     make_float (x),
@@ -10037,6 +10043,12 @@ This variable is ignored on macOS < 10.7 and GNUstep.  Default is t.  */);
 
   DEFSYM (Qx_underline_at_descent_line, "x-underline-at-descent-line");
 
+  DEFVAR_LISP ("ns-scroll-event-delta-factor", Vns_scroll_event_delta_factor,
+               doc: /* A delta to apply to pixel deltas reported in scroll events.
+ This is only effective for pixel deltas generated from touch pads or
+ mice with smooth scrolling capability.  */);
+  Vns_scroll_event_delta_factor = make_float (1.0);
+
   /* Tell Emacs about this window system.  */
   Fprovide (Qns, Qnil);