From acf53f69e0cb0271fecd93dc9b0535a1f24fe2ef Mon Sep 17 00:00:00 2001
From: Daniel Imms <2193314+Tyriar@users.noreply.github.com>
Date: Wed, 2 Aug 2023 11:18:00 -0700
Subject: [PATCH 1/3] Ensure viewport is correctly reset on term.reset

Part of #4603
---
 src/browser/Terminal.ts       |  2 +-
 src/browser/TestUtils.test.ts |  3 +++
 src/browser/Types.d.ts        |  3 ++-
 src/browser/Viewport.ts       | 14 +++++++++++++-
 4 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/src/browser/Terminal.ts b/src/browser/Terminal.ts
index 3f49c82533..c4f8f26e7c 100644
--- a/src/browser/Terminal.ts
+++ b/src/browser/Terminal.ts
@@ -1255,13 +1255,13 @@ export class Terminal extends CoreTerminal implements ITerminal {
     super.reset();
     this._selectionService?.reset();
     this._decorationService.reset();
+    this.viewport?.reset();
 
     // reattach
     this._customKeyEventHandler = customKeyEventHandler;
 
     // do a full screen refresh
     this.refresh(0, this.rows - 1);
-    this.viewport?.syncScrollArea();
   }
 
   public clearTextureAtlas(): void {
diff --git a/src/browser/TestUtils.test.ts b/src/browser/TestUtils.test.ts
index c04c9af202..61918fe15d 100644
--- a/src/browser/TestUtils.test.ts
+++ b/src/browser/TestUtils.test.ts
@@ -324,6 +324,9 @@ export class MockViewport implements IViewport {
   public scrollLines(disp: number): void {
     this._onRequestScrollLines.fire({ amount: disp, suppressScrollEvent: false });
   }
+  public reset(): void {
+    throw new Error('Method not implemented.');
+  }
 }
 
 export class MockCompositionHelper implements ICompositionHelper {
diff --git a/src/browser/Types.d.ts b/src/browser/Types.d.ts
index 42d56c068c..5337a1692e 100644
--- a/src/browser/Types.d.ts
+++ b/src/browser/Types.d.ts
@@ -161,13 +161,14 @@ export interface IPartialColorSet {
 export interface IViewport extends IDisposable {
   scrollBarWidth: number;
   readonly onRequestScrollLines: IEvent<{ amount: number, suppressScrollEvent: boolean }>;
-  syncScrollArea(immediate?: boolean): void;
+  syncScrollArea(immediate?: boolean, force?: boolean): void;
   getLinesScrolled(ev: WheelEvent): number;
   getBufferElements(startLine: number, endLine?: number): { bufferElements: HTMLElement[], cursorElement?: HTMLElement };
   handleWheel(ev: WheelEvent): boolean;
   handleTouchStart(ev: TouchEvent): void;
   handleTouchMove(ev: TouchEvent): boolean;
   scrollLines(disp: number): void;  // todo api name?
+  reset(): void;
 }
 
 export interface ILinkifierEvent {
diff --git a/src/browser/Viewport.ts b/src/browser/Viewport.ts
index a30228a42a..48e973418d 100644
--- a/src/browser/Viewport.ts
+++ b/src/browser/Viewport.ts
@@ -81,13 +81,25 @@ export class Viewport extends Disposable implements IViewport {
     this.register(this._optionsService.onSpecificOptionChange('scrollback', () => this.syncScrollArea()));
 
     // Perform this async to ensure the ICharSizeService is ready.
-    setTimeout(() => this.syncScrollArea(), 0);
+    setTimeout(() => this.syncScrollArea());
   }
 
   private _handleThemeChange(colors: ReadonlyColorSet): void {
     this._viewportElement.style.backgroundColor = colors.background.css;
   }
 
+  public reset(): void {
+    this._currentRowHeight = 0;
+    this._currentDeviceCellHeight = 0;
+    this._lastRecordedBufferLength = 0;
+    this._lastRecordedViewportHeight = 0;
+    this._lastRecordedBufferHeight = 0;
+    this._lastTouchY = 0;
+    this._lastScrollTop = 0;
+    // Sync on next animation frame to ensure the new terminal state is used
+    this._coreBrowserService.window.requestAnimationFrame(() => this.syncScrollArea());
+  }
+
   /**
    * Refreshes row height, setting line-height, viewport height and scroll area height if
    * necessary.

From 91c08ed48e66722352f623a2029ac5c007cba621 Mon Sep 17 00:00:00 2001
From: Daniel Imms <2193314+Tyriar@users.noreply.github.com>
Date: Wed, 2 Aug 2023 11:30:43 -0700
Subject: [PATCH 2/3] Fix clear leaving viewport in a bad state

Fixes #4603
---
 src/browser/Terminal.ts | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/browser/Terminal.ts b/src/browser/Terminal.ts
index c4f8f26e7c..f0ce46947e 100644
--- a/src/browser/Terminal.ts
+++ b/src/browser/Terminal.ts
@@ -1230,8 +1230,11 @@ export class Terminal extends CoreTerminal implements ITerminal {
     for (let i = 1; i < this.rows; i++) {
       this.buffer.lines.push(this.buffer.getBlankLine(DEFAULT_ATTR_DATA));
     }
-    this.refresh(0, this.rows - 1);
+    // IMPORTANT: Fire scroll event before viewport is reset. This ensures embedders get the clear
+    // scroll event and that the viewport's state will be valid for immediate writes.
     this._onScroll.fire({ position: this.buffer.ydisp, source: ScrollSource.TERMINAL });
+    this.viewport?.reset();
+    this.refresh(0, this.rows - 1);
   }
 
   /**

From d2031955ec950912f7e52b7f03602e151d02b921 Mon Sep 17 00:00:00 2001
From: Daniel Imms <2193314+Tyriar@users.noreply.github.com>
Date: Wed, 2 Aug 2023 11:42:40 -0700
Subject: [PATCH 3/3] Remove error from MockViewport.reset

---
 src/browser/TestUtils.test.ts | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/browser/TestUtils.test.ts b/src/browser/TestUtils.test.ts
index 61918fe15d..2015d04637 100644
--- a/src/browser/TestUtils.test.ts
+++ b/src/browser/TestUtils.test.ts
@@ -325,7 +325,6 @@ export class MockViewport implements IViewport {
     this._onRequestScrollLines.fire({ amount: disp, suppressScrollEvent: false });
   }
   public reset(): void {
-    throw new Error('Method not implemented.');
   }
 }