Block toolbar buttons do not scroll with editor content if block toolbar is added manually

packages/ckeditor5-ui/src/toolbar/block/blocktoolbar.ts

@@ -15,6 +15,7 @@ import {
 } from '@ckeditor/ckeditor5-core';
 
 import {
+	global,
 	Rect,
 	ResizeObserver,
 	toUnit,
@@ -29,6 +30,7 @@ import ToolbarView, { NESTED_TOOLBAR_ICONS } from '../toolbarview.js';
 import clickOutsideHandler from '../../bindings/clickoutsidehandler.js';
 import normalizeToolbarConfig from '../normalizetoolbarconfig.js';
 
+import type ButtonView from '../../button/buttonview.js';
 import type { ButtonExecuteEvent } from '../../button/button.js';
 import type { EditorUIReadyEvent, EditorUIUpdateEvent } from '../../editorui/editorui.js';
 
@@ -184,6 +186,9 @@ export default class BlockToolbar extends Plugin {
 			}
 		} );
 
+		// Reposition button on scroll.
+		this._repositionButtonOnScroll();
+
 		// Register the toolbar so it becomes available for Alt+F10 and Esc navigation.
 		editor.ui.addToolbar( this.toolbarView, {
 			beforeFocus: () => this._showPanel(),
@@ -425,21 +430,59 @@ export default class BlockToolbar extends Plugin {
 		}
 	}
 
+	/**
+	 * Repositions the button on scroll.
+	 */
+	private _repositionButtonOnScroll() {
+		const { buttonView } = this;
+
+		let pendingAnimationFrame = false;
+
+		// Reposition the button on scroll, but do it only once per animation frame to avoid performance issues.
+		const repositionOnScroll = () => {
+			if ( pendingAnimationFrame ) {
+				return;
+			}
+
+			pendingAnimationFrame = true;
+			global.window.requestAnimationFrame( () => {
+				this._updateButton();
+				pendingAnimationFrame = false;
+			} );
+		};
+
+		// Watch scroll event only when the button is visible, it prevents attaching the scroll event listener
+		// to the document when the button is not visible.
+		buttonView.on<ObservableChangeEvent<boolean>>( 'change:isVisible', ( evt, name, isVisible ) => {
+			if ( isVisible ) {
+				buttonView.listenTo( global.document, 'scroll', repositionOnScroll, {
+					useCapture: true,
+					usePassive: true
+				} );
+			} else {
+				buttonView.stopListening( global.document, 'scroll', repositionOnScroll );
+			}
+		} );
+	}
+
 	/**
 	 * Attaches the {@link #buttonView} to the target block of content.
 	 *
 	 * @param targetElement Target element.
 	 */
 	private _attachButtonToElement( targetElement: HTMLElement ) {
+		const buttonElement = this.buttonView.element!;
+		const editableElement = this._getSelectedEditableElement();
+
 		const contentStyles = window.getComputedStyle( targetElement );
 
-		const editableRect = new Rect( this._getSelectedEditableElement() );
+		const editableRect = new Rect( editableElement );
 		const contentPaddingTop = parseInt( contentStyles.paddingTop, 10 );
 		// When line height is not an integer then treat it as "normal".
 		// MDN says that 'normal' == ~1.2 on desktop browsers.
 		const contentLineHeight = parseInt( contentStyles.lineHeight, 10 ) || parseInt( contentStyles.fontSize, 10 ) * 1.2;
 
-		const buttonRect = new Rect( this.buttonView.element! );
+		const buttonRect = new Rect( buttonElement );
 		const contentRect = new Rect( targetElement );
 
 		let positionLeft;
@@ -458,6 +501,75 @@ export default class BlockToolbar extends Plugin {
 
 		this.buttonView.top = absoluteButtonRect.top;
 		this.buttonView.left = absoluteButtonRect.left;
+
+		this._clipButtonToViewport( this.buttonView, editableElement );
+	}
+
+	/**
+	 * Clips the button element to the viewport of the editable element.
+	 *
+	 * 	* If the button overflows the editable viewport, it is clipped to make it look like it's cut off by the editable scrollable region.
+	 * 	* If the button is fully hidden by the top of the editable, it is not clickable but still visible in the DOM.
+	 *
+	 * @param buttonView The button view to clip.
+	 * @param editableElement The editable element whose viewport is used for clipping.
+	 */
+	private _clipButtonToViewport(
+		buttonView: ButtonView,
+		editableElement: HTMLElement
+	) {
+		const absoluteButtonRect = new Rect( buttonView.element! );
+		const scrollViewportRect = new Rect( editableElement ).getVisible();
+
+		// Sets polygon clip path for the button element, if there is no argument provided, the clip path is removed.
+		const setButtonClipping = ( ...paths: Array<string> ) => {
+			buttonView.element!.style.clipPath = paths.length ? `polygon(${ paths.join( ',' ) })` : '';
+		};
+
+		// Hide the button if it's fully hidden by the top of the editable.
+		// Note that the button is still visible in the DOM, but it's not clickable. It's because we don't
+		// want to hide the button completely, as there are plenty of `isVisible` watchers which toggles
+		// the button scroll listeners.
+		const markAsHidden = ( isHidden: boolean ) => {
+			buttonView.isEnabled = !isHidden;
+			buttonView.element!.style.pointerEvents = isHidden ? 'none' : '';
+		};
+
+		if ( scrollViewportRect && scrollViewportRect.bottom < absoluteButtonRect.bottom ) {
+			// Calculate the delta between the button bottom and the editable bottom, and clip the button
+			// to make it look like it's cut off by the editable scrollable region.
+			const delta = Math.min(
+				absoluteButtonRect.height,
+				absoluteButtonRect.bottom - scrollViewportRect.bottom
+			);
+
+			markAsHidden( delta >= absoluteButtonRect.height );
+			setButtonClipping(
+				'0 0',
+				'100% 0',
+				`100% calc(100% - ${ toPx( delta ) })`,
+				`0 calc(100% - ${ toPx( delta ) }`
+			);
+		} else if ( scrollViewportRect && scrollViewportRect.top > absoluteButtonRect.top ) {
+			// Calculate the delta between the button top and the editable top, and clip the button
+			// to make it look like it's cut off by the editable scrollable region.
+			const delta = Math.min(
+				absoluteButtonRect.height,
+				scrollViewportRect.top - absoluteButtonRect.top
+			);
+
+			markAsHidden( delta >= absoluteButtonRect.height );
+			setButtonClipping(
+				`0 ${ toPx( delta ) }`,
+				`100% ${ toPx( delta ) }`,
+				'100% 100%',
+				'0 100%'
+			);
+		} else {
+			// Reset the clip path if button is fully visible.
+			markAsHidden( false );
+			setButtonClipping();
+		}
 	}
 
 	/**

packages/ckeditor5-ui/tests/manual/blocktoolbar/scrollable-blocktoolbar.html

@@ -0,0 +1,65 @@
+
+<h2>Scrollable parent:</h2>
+
+<div style="max-height: 300px; max-width: 400px; overflow: auto;">
+	<div id="editor-scrollable-parent">
+		<h2>About CKEditor&nbsp;5</h2>
+
+		<p>This is <a href="https://ckeditor.com">CKEditor&nbsp;5</a>.</p>
+
+		<figure class="image">
+			<img src="./sample.jpg" alt="Autumn fields" />
+		</figure>
+
+		<p>After more than 2 years of building the next generation editor from scratch and closing over 980 tickets, we created a highly <strong>extensible and flexible architecture</strong> which consists of an <strong>amazing editing framework</strong> and <strong>editing solutions</strong> that will be built on top of it.</p>
+
+		<p>We explained this design choice in <a href="https://medium.com/content-uneditable/ckeditor-5-the-future-of-rich-text-editing-2b9300f9df2c">&ldquo;CKEditor 5: The future of rich text editing&ldquo;</a>:</p>
+
+		<blockquote><p>(…) we are changing our approach with CKEditor 5. We will no longer have only two solutions available, instead CKEditor will be seen as a framework for editing solutions. At the same time, we will be developing several out-of-the-box solutions based on it, which will be available to use in many different contexts. It will be a real “one size fits all” approach, from little requirements, to super advanced full featured applications.</p></blockquote>
+
+		<h3>Notes</h3>
+
+		<p><a href="https://ckeditor.com">CKEditor&nbsp;5</a> is <i>under heavy development</i> and this demo is not production-ready software. For example:</p>
+
+		<ul>
+			<li><strong>Only Chrome, Opera and Safari are supported</strong>.</li>
+			<li>Firefox requires enabling the <a href="https://developer.mozilla.org/en-US/docs/Web/API/Document/onselectionchange">&ldquo;dom.select_events.enabled&rdquo;</a> option.</li>
+			<li><a href="https://github.com/ckeditor/ckeditor5/issues/342">Support for pasting</a> is under development (content filtering is unstable).</li>
+		</ul>
+
+		<p>It has <em>bugs</em> that we are aware of &mdash; and that we will be working on in the next few iterations of the project. Stay tuned for some updates soon!</p>
+	</div>
+</div>
+
+<br />
+<br />
+
+<h2>Scrollable editable:</h2>
+
+<div id="editor-scrollable" style="max-height: 300px; max-width: 400px; overflow-y: scroll;">
+	<h2>About CKEditor&nbsp;5</h2>
+
+	<p>This is <a href="https://ckeditor.com">CKEditor&nbsp;5</a>.</p>
+
+	<figure class="image">
+		<img src="./sample.jpg" alt="Autumn fields" />
+	</figure>
+
+	<p>After more than 2 years of building the next generation editor from scratch and closing over 980 tickets, we created a highly <strong>extensible and flexible architecture</strong> which consists of an <strong>amazing editing framework</strong> and <strong>editing solutions</strong> that will be built on top of it.</p>
+
+	<p>We explained this design choice in <a href="https://medium.com/content-uneditable/ckeditor-5-the-future-of-rich-text-editing-2b9300f9df2c">&ldquo;CKEditor 5: The future of rich text editing&ldquo;</a>:</p>
+
+	<blockquote><p>(…) we are changing our approach with CKEditor 5. We will no longer have only two solutions available, instead CKEditor will be seen as a framework for editing solutions. At the same time, we will be developing several out-of-the-box solutions based on it, which will be available to use in many different contexts. It will be a real “one size fits all” approach, from little requirements, to super advanced full featured applications.</p></blockquote>
+
+	<h3>Notes</h3>
+
+	<p><a href="https://ckeditor.com">CKEditor&nbsp;5</a> is <i>under heavy development</i> and this demo is not production-ready software. For example:</p>
+
+	<ul>
+		<li><strong>Only Chrome, Opera and Safari are supported</strong>.</li>
+		<li>Firefox requires enabling the <a href="https://developer.mozilla.org/en-US/docs/Web/API/Document/onselectionchange">&ldquo;dom.select_events.enabled&rdquo;</a> option.</li>
+		<li><a href="https://github.com/ckeditor/ckeditor5/issues/342">Support for pasting</a> is under development (content filtering is unstable).</li>
+	</ul>
+
+	<p>It has <em>bugs</em> that we are aware of &mdash; and that we will be working on in the next few iterations of the project. Stay tuned for some updates soon!</p>
+</div>

packages/ckeditor5-ui/tests/manual/blocktoolbar/scrollable-blocktoolbar.js

@@ -0,0 +1,39 @@
+/**
+ * @license Copyright (c) 2003-2024, CKSource Holding sp. z o.o. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/* globals window, document, console:false */
+
+import BalloonEditor from '@ckeditor/ckeditor5-editor-balloon/src/ballooneditor.js';
+import Essentials from '@ckeditor/ckeditor5-essentials/src/essentials.js';
+import List from '@ckeditor/ckeditor5-list/src/list.js';
+import Image from '@ckeditor/ckeditor5-image/src/image.js';
+import ImageCaption from '@ckeditor/ckeditor5-image/src/imagecaption.js';
+import { Paragraph, ParagraphButtonUI } from '@ckeditor/ckeditor5-paragraph';
+import Heading from '@ckeditor/ckeditor5-heading/src/heading.js';
+import HeadingButtonsUI from '@ckeditor/ckeditor5-heading/src/headingbuttonsui.js';
+import BlockToolbar from '../../../src/toolbar/block/blocktoolbar.js';
+
+createBlockButtonEditor( '#editor-scrollable-parent' ).then( editor => {
+	window.editor = editor;
+} );
+
+createBlockButtonEditor( '#editor-scrollable' ).then( editor => {
+	window.editor2 = editor;
+} );
+
+function createBlockButtonEditor( element ) {
+	return BalloonEditor
+		.create( document.querySelector( element ), {
+			plugins: [ Essentials, List, Paragraph, Heading, Image, ImageCaption, HeadingButtonsUI, ParagraphButtonUI, BlockToolbar ],
+			blockToolbar: [
+				'paragraph', 'heading1', 'heading2', 'heading3', 'bulletedList', 'numberedList', 'paragraph',
+				'heading1', 'heading2', 'heading3', 'bulletedList', 'numberedList', 'paragraph', 'heading1', 'heading2', 'heading3',
+				'bulletedList', 'numberedList'
+			]
+		} )
+		.catch( err => {
+			console.error( err.stack );
+		} );
+}

packages/ckeditor5-ui/tests/manual/blocktoolbar/scrollable-blocktoolbar.md

@@ -0,0 +1,3 @@
+# Scrollable block toolbar
+
+The manual test that allows testing various block toolbar behavior within scrollable containers.