fix bug horizontal scroll when hiddenDates are present

lib/timeline/Core.js

@@ -281,12 +281,13 @@ class Core {
         this.range.stopRolling();
 
         // Depending on the mouse wheel used chose the delta (some mice have the hardware for both)
-        const delta = isCurrentlyScrollingWithVerticalScrollWheel
-          ? deltaY
-          : deltaX;
+				const delta = isCurrentlyScrollingWithVerticalScrollWheel ? deltaY : deltaX;
 
-        // Calculate a single scroll jump relative to the range scale
-        let diff = ((delta / 120) * (this.range.end - this.range.start)) / 20;
+				// Calculate visual range (excluding hidden periods) for consistent scroll speed
+				const absoluteRange = this.range.end - this.range.start;
+				const hiddenDuration = DateUtil.getHiddenDurationBetween(this.body.hiddenDates, this.range.start, this.range.end);
+				const visualRange = absoluteRange - hiddenDuration;
+				let diff = delta / 120 * visualRange / 20;
 
         // Invert scroll direction
         //  ...unless the user uses a horizontal mouse-wheel as found on the "Logi Master" series.
@@ -298,17 +299,27 @@ class Core {
         )
           diff = -diff;
 
-        // calculate new start and end
-        const newStart = this.range.start + diff;
-        const newEnd = this.range.end + diff;
-        const options = {
-          animation: false,
-          byUser: true,
-          event: event,
-        };
-        this.range.setRange(newStart, newEnd, options);
-
-        event.preventDefault();
+        // Apply visual shift preserving visual span (like pinch-to-zoom does)
+				const currentVisualSpan = visualRange;
+				let newStart = this.range.start + diff;
+				let newEnd = this.range.end + diff;
+
+				// If crossing hidden boundaries, preserve visual span
+				const newHiddenDuration = DateUtil.getHiddenDurationBetween(this.body.hiddenDates, newStart, newEnd);
+				const newAbsoluteSpan = currentVisualSpan + newHiddenDuration;
+				newEnd = newStart + newAbsoluteSpan;
+
+				// snapping times away from hidden zones (same as pinch-to-zoom)
+				const safeStart = DateUtil.snapAwayFromHidden(this.body.hiddenDates, newStart, diff, true);
+				const safeEnd = DateUtil.snapAwayFromHidden(this.body.hiddenDates, newEnd, -diff, true);
+
+				const options = {
+					animation: false,
+					byUser: true,
+					event: event
+				};
+				this.range.setRange(safeStart, safeEnd, options);
+				event.preventDefault();
 
         // Here in case of any future behaviour following after
         return;