From 36400c7dc9c8d46f956f42d4bdbb6fe7b3f8c30a Mon Sep 17 00:00:00 2001
From: Alan Third <alan@idiocy.org>
Date: Thu, 2 Nov 2017 21:41:11 +0000
Subject: [PATCH] Fix mouse-scrollbar offset on GNUstep and old macOS
 (bug#29053)

* src/nsterm.m (EmacsScroller::mouseDown,
EmacsScroller::mouseDragged): Take scroller buttons into account when
calculating scroller knob position.
---
 src/nsterm.m | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/nsterm.m b/src/nsterm.m
index a382e5f7130..5c29f039e51 100644
--- a/src/nsterm.m
+++ b/src/nsterm.m
@@ -8912,10 +8912,20 @@ - (void)mouseDown: (NSEvent *)e
         }
       last_mouse_offset = kloc;
 
-      if (part != NSScrollerKnob)
-        /* this is a slot click on GNUstep: go straight there */
+      /* if knob, tell emacs a location offset by knob pos
+         (to indicate top of handle) */
+      if (part == NSScrollerKnob)
+        pos = (loc - last_mouse_offset);
+      else
+        /* else this is a slot click on GNUstep: go straight there */
         pos = loc;
 
+      /* If there are buttons in the scroller area, we need to
+         recalculate pos as emacs expects the scroller slot to take up
+         the entire available length.  */
+      if (length != pixel_length)
+        pos = pos * pixel_length / length;
+
       /* send a fake mouse-up to super to preempt modal -trackKnob: mode */
       fake_event = [NSEvent mouseEventWithType: NSEventTypeLeftMouseUp
                                       location: [e locationInWindow]
@@ -8980,6 +8990,13 @@ - (void)mouseDragged: (NSEvent *)e
         }
 
       pos = (loc - last_mouse_offset);
+
+      /* If there are buttons in the scroller area, we need to
+         recalculate pos as emacs expects the scroller slot to take up
+         the entire available length.  */
+      if (length != pixel_length)
+        pos = pos * pixel_length / length;
+
       [self sendScrollEventAtLoc: pos fromEvent: e];
 }