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.

1 files changed, 19 insertions, 0 deletions

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