>From 1c9ca5b5d38274eb1a2eb2aa28ef43ac4670d3a6 Mon Sep 17 00:00:00 2001
From: Alan Third <address@hidden>
Date: Fri, 8 Sep 2017 19:26:47 +0100
Subject: [PATCH] Provide smoother touchpad scrolling on macOS

* lisp/term/ns-win.el (mouse-wheel-scroll-amount,
mouse-wheel-progressive-speed): Set to smarter values for touchpads.
* src/nsterm.m (emacsView::mouseDown): Use precise scrolling deltas to
calculate scrolling for touchpads.
---
 lisp/term/ns-win.el |  9 ++++++
 src/nsterm.m        | 91 ++++++++++++++++++++++++++++++++++++++++++++++-------
 2 files changed, 88 insertions(+), 12 deletions(-)

diff --git a/lisp/term/ns-win.el b/lisp/term/ns-win.el
index cfce83f892..488ea9cf0b 100644
--- a/lisp/term/ns-win.el
+++ b/lisp/term/ns-win.el
@@ -736,6 +736,15 @@ ns-paste-secondary
 (global-unset-key [horizontal-scroll-bar drag-mouse-1])
 
 
+;;;; Sane defaults for trackpad scrolling.
+
+;; These aren't so good for mousewheel scrolling, but we can't
+;; differentiate between the two.
+
+(setq mouse-wheel-scroll-amount '(1 ((shift) . 5)))
+(setq mouse-wheel-progressive-speed nil)
+
+
 ;;;; Color support.
 
 ;; Functions for color panel + drag
diff --git a/src/nsterm.m b/src/nsterm.m
index be97e94dd5..432e4ada86 100644
--- a/src/nsterm.m
+++ b/src/nsterm.m
@@ -6498,24 +6498,91 @@ - (void)mouseDown: (NSEvent *)theEvent
 
   if ([theEvent type] == NSEventTypeScrollWheel)
     {
-      CGFloat delta = [theEvent deltaY];
-      /* Mac notebooks send wheel events w/delta =0 when trackpad scrolling */
-      if (delta == 0)
+#if defined (NS_IMPL_COCOA) && MAC_OS_X_VERSION_MAX_ALLOWED >= 1070
+      /* If the input device is a touchpad or similar, use precise
+       * scrolling deltas.  These are measured in pixels, so we have
+       * to add them up until they exceed one line height, then we can
+       * send one, or more, scroll wheel events.
+       *
+       * If the device only has coarse scrolling deltas, like a real
+       * mousewheel, use the old method which sends one scroll event
+       * per mousewheel `click'.  We could use precise deltas here
+       * too, but they can result in as little as one pixel change per
+       * `click', which would make it appear to the user as though
+       * nothing was happening.
+       */
+
+      if ([theEvent hasPreciseScrollingDeltas])
         {
-          delta = [theEvent deltaX];
-          if (delta == 0)
+          static int totalDeltaX, totalDeltaY;
+          bool horizontal;
+          int lines = 0;
+          int lineHeight = default_line_pixel_height(XWINDOW (FRAME_SELECTED_WINDOW (emacsframe)));
+
+          if ([theEvent phase] == NSEventPhaseBegan)
+            {
+              totalDeltaX = 0;
+              totalDeltaY = 0;
+            }
+
+          totalDeltaX += [theEvent scrollingDeltaX];
+          totalDeltaY += [theEvent scrollingDeltaY];
+
+          /* Calculate the number of lines, if any, to scroll, and
+           * reset the total delta for the direction we're NOT
+           * scrolling so that small movements don't add up.  */
+          if (abs (totalDeltaX) > abs (totalDeltaY)
+              && abs (totalDeltaX) > lineHeight)
+            {
+              horizontal = YES;
+              lines = totalDeltaX / lineHeight;
+              totalDeltaX = totalDeltaX % lineHeight;
+              totalDeltaY = 0;
+            }
+          else if (abs (totalDeltaY) >= abs (totalDeltaX)
+                   && abs (totalDeltaY) > lineHeight)
+            {
+              horizontal = NO;
+              lines = totalDeltaY / lineHeight;
+              totalDeltaY = totalDeltaY % lineHeight;
+              totalDeltaX = 0;
+            }
+
+          for (int i = 0 ; i < abs (lines) ; i++)
             {
-              NSTRACE_MSG ("deltaIsZero");
-              return;
+              emacs_event->kind = horizontal ? HORIZ_WHEEL_EVENT : WHEEL_EVENT;
+
+              emacs_event->code = 0;
+              emacs_event->modifiers = EV_MODIFIERS (theEvent) |
+                ((lines > 0) ? up_modifier : down_modifier);
+              XSETINT (emacs_event->x, lrint (p.x));
+              XSETINT (emacs_event->y, lrint (p.y));
+              EV_TRAILER (theEvent);
             }
-          emacs_event->kind = HORIZ_WHEEL_EVENT;
+          return;
         }
       else
-        emacs_event->kind = WHEEL_EVENT;
+#endif /* defined (NS_IMPL_COCOA) && MAC_OS_X_VERSION_MAX_ALLOWED >= 1070 */
+        {
+          CGFloat delta = [theEvent deltaY];
+          /* Mac notebooks send wheel events w/delta =0 when trackpad scrolling */
+          if (delta == 0)
+            {
+              delta = [theEvent deltaX];
+              if (delta == 0)
+                {
+                  NSTRACE_MSG ("deltaIsZero");
+                  return;
+                }
+              emacs_event->kind = HORIZ_WHEEL_EVENT;
+            }
+          else
+            emacs_event->kind = WHEEL_EVENT;
 
-      emacs_event->code = 0;
-      emacs_event->modifiers = EV_MODIFIERS (theEvent) |
-        ((delta > 0) ? up_modifier : down_modifier);
+          emacs_event->code = 0;
+          emacs_event->modifiers = EV_MODIFIERS (theEvent) |
+            ((delta > 0) ? up_modifier : down_modifier);
+        }
     }
   else
     {
-- 
2.12.0