From ea3cda979101d1028671f00ed37c998893abbcd4 Mon Sep 17 00:00:00 2001
From: dmitry <dmitry@lazarus-ide.org>
Date: Wed, 28 Aug 2019 02:26:38 +0000
Subject: [PATCH] cocoa: correct horizontal scrollWheel. macOS and LCL are
 using reversed delta values

git-svn-id: trunk@61770 -
---
 lcl/interfaces/cocoa/cocoawscommon.pas | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lcl/interfaces/cocoa/cocoawscommon.pas b/lcl/interfaces/cocoa/cocoawscommon.pas
index bae9aac653..2487bc0547 100644
--- a/lcl/interfaces/cocoa/cocoawscommon.pas
+++ b/lcl/interfaces/cocoa/cocoawscommon.pas
@@ -1161,7 +1161,10 @@ begin
   if event.deltaX <> 0 then
   begin
     Msg.Msg := LM_MOUSEHWHEEL;
-    Msg.WheelDelta := round(event.deltaX * 120);
+    // see "deltaX" documentation.
+    // on macOS: -1 = right, +1 = left
+    // on LCL:   -1 = left,  +1 = right
+    Msg.WheelDelta := round(-event.deltaX * 120);
   end
   else
     // Filter out empty events - See bug 28491