From 38913e4ae15289227b79da4f9004e1ccd608071c Mon Sep 17 00:00:00 2001
From: Daniel Imms <2193314+Tyriar@users.noreply.github.com>
Date: Sat, 7 Feb 2026 16:09:03 -0800
Subject: [PATCH] Fix scrolling with touch

Part of #5377
---
 src/browser/CoreBrowserTerminal.ts | 73 ++++++++++++++++++++++++++++++
 src/browser/Viewport.ts            | 12 ++---
 src/browser/scrollable/touch.ts    |  4 ++
 3 files changed, 80 insertions(+), 9 deletions(-)

diff --git a/src/browser/CoreBrowserTerminal.ts b/src/browser/CoreBrowserTerminal.ts
index 8ad8409f4..607b12199 100644
--- a/src/browser/CoreBrowserTerminal.ts
+++ b/src/browser/CoreBrowserTerminal.ts
@@ -57,6 +57,7 @@ import { AccessibilityManager } from './AccessibilityManager';
 import { Linkifier } from './Linkifier';
 import { Emitter, EventUtils, type IEvent } from 'common/Event';
 import { addDisposableListener } from 'browser/Dom';
+import { Gesture, EventType as GestureEventType, type IGestureEvent } from 'browser/scrollable/touch';
 import { MutableDisposable, toDisposable } from 'common/Lifecycle';
 
 export class CoreBrowserTerminal extends CoreTerminal implements ITerminal {
@@ -78,6 +79,7 @@ export class CoreBrowserTerminal extends CoreTerminal implements ITerminal {
 
   private _customKeyEventHandler: CustomKeyEventHandler | undefined;
   private _customWheelEventHandler: CustomWheelEventHandler | undefined;
+  private _touchScrollAccumulator: number = 0;
 
   // Browser services
   private readonly _decorationService: DecorationService;
@@ -914,9 +916,80 @@ export class CoreBrowserTerminal extends CoreTerminal implements ITerminal {
         return false;
       }
     }, { passive: false }));
+
+    // Touch/gesture scrolling support
+    this._register(Gesture.addTarget(this.screenElement!));
+    this._register(addDisposableListener(this.screenElement!, GestureEventType.START, () => {
+      this._touchScrollAccumulator = 0;
+    }));
+    this._register(addDisposableListener(this.screenElement!, GestureEventType.CHANGE, (e: IGestureEvent) => {
+      e.preventDefault();
+      e.stopPropagation();
+
+      // When mouse protocol has wheel events active, send as mouse wheel events
+      if (requestedEvents.wheel) {
+        this._handleTouchScrollAsWheel(e, sendEvent);
+        return;
+      }
+
+      // When in alt buffer (no scrollback), send up/down key sequences
+      if (!this.buffer.hasScrollback) {
+        this._handleTouchScrollAsKeys(e);
+        return;
+      }
+
+      // Normal scrollback: delegate to viewport
+      this._viewport?.handleTouchScroll(e.translationY);
+    }));
   }
 
 
+  private _handleTouchScrollAsKeys(e: IGestureEvent): void {
+    const cellHeight = this._renderService?.dimensions.css.cell.height;
+    if (!cellHeight) return;
+
+    this._touchScrollAccumulator -= e.translationY;
+    const lines = Math.trunc(this._touchScrollAccumulator / cellHeight);
+    if (lines === 0) return;
+
+    this._touchScrollAccumulator -= lines * cellHeight;
+    const sequence = C0.ESC
+      + (this.coreService.decPrivateModes.applicationCursorKeys ? 'O' : '[')
+      + (lines < 0 ? 'A' : 'B');
+    for (let i = 0; i < Math.abs(lines); i++) {
+      this.coreService.triggerDataEvent(sequence, true);
+    }
+  }
+
+  private _handleTouchScrollAsWheel(e: IGestureEvent, sendEvent: (ev: MouseEvent | WheelEvent) => boolean): void {
+    const cellHeight = this._renderService?.dimensions.css.cell.height;
+    if (!cellHeight) return;
+
+    this._touchScrollAccumulator -= e.translationY;
+    const lines = Math.trunc(this._touchScrollAccumulator / cellHeight);
+    if (lines === 0) return;
+
+    this._touchScrollAccumulator -= lines * cellHeight;
+
+    // Get coordinates from gesture event
+    const pos = this._mouseService?.getMouseReportCoords(e, this.screenElement!);
+    if (!pos) return;
+
+    for (let i = 0; i < Math.abs(lines); i++) {
+      this.coreMouseService.triggerMouseEvent({
+        col: pos.col,
+        row: pos.row,
+        x: pos.x,
+        y: pos.y,
+        button: CoreMouseButton.WHEEL,
+        action: lines < 0 ? CoreMouseAction.UP : CoreMouseAction.DOWN,
+        ctrl: false,
+        alt: false,
+        shift: false
+      });
+    }
+  }
+
   /**
    * Tells the renderer to refresh terminal content between two rows (inclusive) at the next
    * opportunity.
diff --git a/src/browser/Viewport.ts b/src/browser/Viewport.ts
index 09864f7ac..fd98ab7cc 100644
--- a/src/browser/Viewport.ts
+++ b/src/browser/Viewport.ts
@@ -8,12 +8,11 @@ import { ViewportConstants } from 'browser/shared/Constants';
 import { Disposable, toDisposable } from 'common/Lifecycle';
 import { IBufferService, ICoreMouseService, IOptionsService } from 'common/services/Services';
 import { CoreMouseEventType } from 'common/Types';
-import { addDisposableListener, scheduleAtNextAnimationFrame } from 'browser/Dom';
+import { scheduleAtNextAnimationFrame } from 'browser/Dom';
 import { SmoothScrollableElement } from 'browser/scrollable/scrollableElement';
 import type { IScrollableElementChangeOptions } from 'browser/scrollable/scrollableElementOptions';
 import { Emitter, EventUtils } from 'common/Event';
 import { Scrollable, ScrollbarVisibility, type IScrollEvent } from 'browser/scrollable/scrollable';
-import { Gesture, EventType as GestureEventType, type IGestureEvent } from 'browser/scrollable/touch';
 
 export class Viewport extends Disposable {
 
@@ -107,9 +106,6 @@ export class Viewport extends Disposable {
 
     this._register(this._scrollableElement.onScroll(e => this._handleScroll(e)));
 
-    // Touch/gesture scrolling support
-    this._register(Gesture.addTarget(screenElement));
-    this._register(addDisposableListener(screenElement, GestureEventType.CHANGE, (e: IGestureEvent) => this._handleGestureChange(e)));
   }
 
   public scrollLines(disp: number): void {
@@ -204,12 +200,10 @@ export class Viewport extends Disposable {
     this._isHandlingScroll = false;
   }
 
-  private _handleGestureChange(e: IGestureEvent): void {
-    e.preventDefault();
-    e.stopPropagation();
+  public handleTouchScroll(translationY: number): void {
     const pos = this._scrollableElement.getScrollPosition();
     this._scrollableElement.setScrollPosition({
-      scrollTop: pos.scrollTop - e.translationY
+      scrollTop: pos.scrollTop - translationY
     });
   }
 }
diff --git a/src/browser/scrollable/touch.ts b/src/browser/scrollable/touch.ts
index cba4e5b57..8ffdfe699 100644
--- a/src/browser/scrollable/touch.ts
+++ b/src/browser/scrollable/touch.ts
@@ -153,6 +153,8 @@ export interface IGestureEvent extends MouseEvent {
   translationY: number;
   pageX: number;
   pageY: number;
+  clientX: number;
+  clientY: number;
   tapCount: number;
 }
 
@@ -459,6 +461,8 @@ export class Gesture extends Disposable {
       evt.translationY = touch.pageY - tail(data.rollingPageY)!;
       evt.pageX = touch.pageX;
       evt.pageY = touch.pageY;
+      evt.clientX = touch.clientX;
+      evt.clientY = touch.clientY;
       this._dispatchEvent(evt);
 
       if (data.rollingPageX.length > 3) {