It’s surprisingly pleasant to use (with a Mac laptop, a Magic Trackpad or
aMagic Mouse)

Demo here: https://www.youtube.com/watch?v=1XJFJ4coS48&feature=youtu.be

commit d782c880d4ca30fcacddfbab298dad82fe8277c3
Author: marius a. eriksen <marius@grailbio.com>
Date:   Sat Feb 25 21:48:50 2017 -0800

    devdraw/acme: support for inertial scrolling on macOS.

diff --git a/src/cmd/acme/acme.c b/src/cmd/acme/acme.c
index b471a29..d84322f 100644
--- a/src/cmd/acme/acme.c
+++ b/src/cmd/acme/acme.c
@@ -614,6 +614,14 @@ mousethread(void *v)
  }
  /* scroll buttons, wheels, etc. */
  if(w != nil && (m.buttons & (8|16))){
+ if((m.buttons >> 2) != 0){
+ winlock(w, 'M');
+ t->eq0 = ~0;
+ xtextscroll(t, m.buttons>>2);
+ winunlock(w);
+ goto Continue;
+ }
+
  if(m.buttons & 8)
  but = Kscrolloneup;
  else
diff --git a/src/cmd/acme/text.c b/src/cmd/acme/text.c
index 7634d92..72b29c2 100644
--- a/src/cmd/acme/text.c
+++ b/src/cmd/acme/text.c
@@ -653,6 +653,35 @@ textcomplete(Text *t)
  return rp;
 }

+void
+xtextscroll(Text *t, int n)
+{
+ uint q0;
+
+
+ if(n == 0)
+ return;
+
+ if(t->what == Tag){
+ if(n<0)
+ texttype(t, Kscrolloneup);
+ else
+ texttype(t, Kscrollonedown);
+ return;
+ }
+
+ fprint(2, "n=%d\n", n);
+
+ if(n < 0){
+ n = -n;
+ q0 = t->org+frcharofpt(&t->fr, Pt(t->fr.r.min.x,
t->fr.r.min.y+n*t->fr.font->height));
+ textsetorigin(t, q0, TRUE);
+ }else{
+ q0 = textbacknl(t, t->org, n);
+ textsetorigin(t, q0, TRUE);
+ }
+}
+
 void
 texttype(Text *t, Rune r)
 {
diff --git a/src/cmd/devdraw/cocoa-screen.m b/src/cmd/devdraw/cocoa-screen.m
index 100cdd5..b83a3ff 100644
--- a/src/cmd/devdraw/cocoa-screen.m
+++ b/src/cmd/devdraw/cocoa-screen.m
@@ -1044,7 +1044,8 @@ static void
 getmouse(NSEvent *e)
 {
  float d;
- int b, m;
+ int b, m, i;
+ static int accum;

  if([WIN isKeyWindow] == 0)
  return;
@@ -1080,11 +1081,22 @@ getmouse(NSEvent *e)
 #else
  d = [e deltaY];
 #endif
+
+
+// fprint(2, "delta: %d\n", (short)d);
+
+ //fprint(2, "d: %f %d\n", d, [e hasPreciseScrollingDeltas]);
+
+ if((short)d==0)
+ return;
+
  if(d>0)
  in.mscroll = 8;
  else
  if(d<0)
  in.mscroll = 16;
+
+ in.mscroll |= ((short)d)<<1;
  break;

  case NSMouseMoved: