Provide native touchpad scrolling on macOS

* etc/NEWS: Describe changes.
* lisp/term/ns-win.el (mouse-wheel-scroll-amount,
mouse-wheel-progressive-speed): Set to smarter values for macOS
touchpads.
* src/nsterm.m (emacsView::mouseDown): Use precise scrolling deltas to
calculate scrolling for touchpads and mouse wheels.
(syms_of_nsterm): Add variables 'ns-use-system-mwheel-acceleration',
'ns-touchpad-scroll-line-height' and 'ns-touchpad-use-momentum'.
* src/keyboard.c (make_lispy_event): Pass on .arg when relevant.
* src/termhooks.h (event_kind): Update comments re. WHEEL_EVENT.
* lisp/mwheel.el (mwheel-scroll): Use line count.
* lisp/subr.el (event-line-count): New function.

3 files changed, 25 insertions, 0 deletions

diff --git a/lisp/mwheel.el b/lisp/mwheel.el
index 2956ba55162..0c0dcb3beb1 100644
--- a/lisp/mwheel.el
+++ b/lisp/mwheel.el
@@ -232,6 +232,7 @@ non-Windows systems."
       ;; When the double-mouse-N comes in, a mouse-N has been executed already,
       ;; So by adding things up we get a squaring up (1, 3, 6, 10, 15, ...).
       (setq amt (* amt (event-click-count event))))
+    (when (numberp amt) (setq amt (* amt (event-line-count event))))
     (unwind-protect
         (let ((button (mwheel-event-button event)))
           (cond ((eq button mouse-wheel-down-event)
diff --git a/lisp/subr.el b/lisp/subr.el
index 96b1ac19b4b..cf15ec287ff 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -1270,6 +1270,11 @@ See `event-start' for a description of the value returned."
   "Return the multi-click count of EVENT, a click or drag event.
 The return value is a positive integer."
   (if (and (consp event) (integerp (nth 2 event))) (nth 2 event) 1))
+
+(defsubst event-line-count (event)
+  "Return the line count of EVENT, a mousewheel event.
+The return value is a positive integer."
+  (if (and (consp event) (integerp (nth 3 event))) (nth 3 event) 1))
 
 ;;;; Extracting fields of the positions in an event.
 
diff --git a/lisp/term/ns-win.el b/lisp/term/ns-win.el
index 68b659bf751..bc211ea9589 100644
--- a/lisp/term/ns-win.el
+++ b/lisp/term/ns-win.el
@@ -736,6 +736,25 @@ See the documentation of `create-fontset-from-fontset-spec' for the format.")
 (global-unset-key [horizontal-scroll-bar drag-mouse-1])
 
 
+;;;; macOS-like defaults for trackpad and mouse wheel scrolling on
+;;;; macOS 10.7+.
+
+;; FIXME: This doesn't look right.  Is there a better way to do this
+;; that keeps customize happy?
+(let ((appkit-version (progn
+                        (string-match "^appkit-\\([^\s-]*\\)" ns-version-string)
+                        (string-to-number (match-string 1 ns-version-string)))))
+  ;; Appkit 1138 ~= macOS 10.7.
+  (when (and (featurep 'cocoa) (>= appkit-version 1138))
+    (setq mouse-wheel-scroll-amount '(1 ((shift) . 5) ((control))))
+    (put 'mouse-wheel-scroll-amount 'customized-value
+         (list (custom-quote (symbol-value 'mouse-wheel-scroll-amount))))
+
+    (setq mouse-wheel-progressive-speed nil)
+    (put 'mouse-wheel-progressive-speed 'customized-value
+         (list (custom-quote (symbol-value 'mouse-wheel-progressive-speed))))))
+
+
 ;;;; Color support.
 
 ;; Functions for color panel + drag