fix: add horizontal mouse wheel scrolling

Src/SourceGrid/Common/CustomScrollControl.cs

@@ -696,11 +696,11 @@ public virtual void CustomScrollPageLeft()
             if (HScrollBarVisible)
                 mHScrollBar.Value = Math.Max(mHScrollBar.Value - mHScrollBar.LargeChange, mHScrollBar.Minimum);
         }
-        public virtual void CustomScrollWheel(int rotationDelta)
+        public virtual void CustomScrollWheel(int rotationDelta, bool asVertical)
         {
             if (rotationDelta >= 120 || rotationDelta <= -120)
             {
-                if (VScrollBarVisible)
+                if (asVertical && VScrollBarVisible)
                 {
                     Point current = CustomScrollPosition;
                     int newY = current.Y +
@@ -714,6 +714,20 @@ public virtual void CustomScrollWheel(int rotationDelta)
 
                     CustomScrollPosition = new Point(current.X, newY);
                 }
+                else if (!asVertical && HScrollBarVisible)
+                {
+                    Point current = CustomScrollPosition;
+                    int newX = current.X +
+                        SystemInformation.MouseWheelScrollLines * HScrollBar.SmallChange * -Math.Sign(rotationDelta);
+
+                    //check that the value is between max and min
+                    if (newX < 0)
+                        newX = 0;
+                    if (newX > MaximumHScroll)
+                        newX = MaximumHScroll;
+
+                    CustomScrollPosition = new Point(newX, current.Y);
+                }
             }
         }
 

Src/SourceGrid/Grids/GridVirtual.cs

@@ -2101,7 +2101,54 @@ protected override void OnMouseWheel(MouseEventArgs e)
         {
             base.OnMouseWheel(e);
 
-            CustomScrollWheel(e.Delta);
+            // Check if shift key is being held down to simulate horizontal scroll
+            bool asVertical = (Control.ModifierKeys & Keys.Shift) != Keys.Shift;
+
+            CustomScrollWheel(e.Delta, asVertical);
+        }
+
+        protected virtual void OnMouseHWheel(MouseEventArgs e)
+        {
+            // Invert delta to match handling and scroll direction in Excel
+            CustomScrollWheel(-1 * e.Delta, false);
+        }
+
+        private static class NativeMethods
+        {
+            internal static int SignedHIWORD(IntPtr ptr)
+            {
+                unchecked
+                {
+                    int n = (int)(long)ptr;
+                    return (short)((n >> 16) & (int)ushort.MaxValue);
+                }
+            }
+
+            internal static int SignedLOWORD(IntPtr ptr)
+            {
+                unchecked
+                {
+                    int n = (int)(long)ptr;
+                    return (short)(n & (int)ushort.MaxValue);
+                }
+            }
+        }
+
+        protected override void WndProc(ref Message m)
+        {
+            const int WM_MOUSEHWHEEL = 0x020E;
+            if (m.Msg == WM_MOUSEHWHEEL)
+            {
+                Point p = new Point(NativeMethods.SignedLOWORD(m.LParam), NativeMethods.SignedHIWORD(m.LParam));
+                p = PointToClient(p);
+                OnMouseHWheel(new MouseEventArgs(MouseButtons.None, 0, p.X, p.Y, NativeMethods.SignedHIWORD(m.WParam)));
+
+                // Set as handled and do not call base method (same as Control.WmMouseWheel)
+                m.Result = (IntPtr)1;
+                return;
+            }
+
+            base.WndProc(ref m);
         }
 
         #endregion