Try SVG-based duotone filter

blocks/duotone-filter/duotone.php

@@ -0,0 +1,60 @@
+<?php
+
+if ( ! function_exists( 'hex2rgb' ) ) {
+	function hex2rgb( $color ) {
+		if ( strlen( $color ) === 4 ) {
+			$r = hexdec( substr( $color, 1, 1 ) . substr( $color, 1, 1 ) );
+			$g = hexdec( substr( $color, 2, 1 ) . substr( $color, 2, 1 ) );
+			$b = hexdec( substr( $color, 3, 1 ) . substr( $color, 3, 1 ) );
+		} elseif ( strlen( $color ) === 7 ) {
+			$r = hexdec( substr( $color, 1, 2 ) );
+			$g = hexdec( substr( $color, 3, 2 ) );
+			$b = hexdec( substr( $color, 5, 2 ) );
+		} else {
+			return array();
+		}
+
+		return array(
+			'r' => $r / 0xff,
+			'g' => $g / 0xff,
+			'b' => $b / 0xff,
+		);
+	}
+}
+
+// phpcs:disable
+$duotone_id = $block['attrs']['duotoneId'];
+$duotone_dark = hex2rgb( $block['attrs']['duotoneDark'] );
+$duotone_light = hex2rgb( $block['attrs']['duotoneLight'] );
+// phpcs:enable
+
+?>
+
+<svg
+	xmlns:xlink="http://www.w3.org/1999/xlink"
+	viewBox="0 0 0 0"
+	width="0"
+	height="0"
+	focusable="false"
+	role="none"
+	style="visibility: hidden !important; position: absolute !important; left: -9999px !important; overflow: hidden !important;"
+>
+	<defs>
+		<filter id="<?php echo $duotone_id; ?>">
+			<feColorMatrix
+				type="matrix"
+				<?php // phpcs:disable ?>
+				values=".2989 .5870 .1140 0 0
+				        .2989 .5870 .1140 0 0
+				        .2989 .5870 .1140 0 0
+				        0 0 0 1 0"
+				<?php // phpcs:enable ?>
+			/>
+			<feComponentTransfer color-interpolation-filters="sRGB">
+				<feFuncR type="table" tableValues="<?php echo $duotone_dark['r']; ?> <?php echo $duotone_light['r']; ?>" />
+				<feFuncG type="table" tableValues="<?php echo $duotone_dark['g']; ?> <?php echo $duotone_light['g']; ?>" />
+				<feFuncB type="table" tableValues="<?php echo $duotone_dark['b']; ?> <?php echo $duotone_light['b']; ?>" />
+			</feComponentTransfer>
+		</filter>
+	</defs>
+</svg>

blocks/duotone-filter/index.php

@@ -0,0 +1,31 @@
+<?php
+
+add_action( 'init', function() {
+	register_block_type( 'a8c/duotone-filter', [
+		'editor_script' => 'block-experiments',
+		'style' => 'block-experiments',
+		'editor_style' => 'block-experiments-editor',
+	] );
+
+	function is_supported_block( $block ) {
+		$supported_blocks = [ 'core/image', 'core/cover' ];
+		return in_array( $block['blockName'], $supported_blocks, true );
+	}
+
+	add_filter( 'render_block', function ( $block_content, $block ) {
+		if (
+			! is_supported_block( $block ) ||
+			! array_key_exists( 'duotoneId', $block['attrs'] ) ||
+			! array_key_exists( 'duotoneDark', $block['attrs'] ) ||
+			! array_key_exists( 'duotoneLight', $block['attrs'] )
+		) {
+			return $block_content;
+		}
+
+		ob_start();
+		include 'duotone.php';
+		$duotone = ob_get_clean();
+
+		return $duotone . $block_content;
+	}, 10, 2 );
+} );

blocks/duotone-filter/src/duotone.js

@@ -0,0 +1,79 @@
+/**
+ * WordPress dependencies
+ */
+import { SVG } from '@wordpress/components';
+
+const hex2rgb = ( color = '' ) => {
+	let r = '0';
+	let g = '0';
+	let b = '0';
+
+	if ( color.length === 4 ) {
+		r = '0x' + color[ 1 ] + color[ 1 ];
+		g = '0x' + color[ 2 ] + color[ 2 ];
+		b = '0x' + color[ 3 ] + color[ 3 ];
+	} else if ( color.length === 7 ) {
+		r = '0x' + color[ 1 ] + color[ 2 ];
+		g = '0x' + color[ 3 ] + color[ 4 ];
+		b = '0x' + color[ 5 ] + color[ 6 ];
+	} else {
+		return {};
+	}
+
+	return {
+		r: r / 0xff,
+		g: g / 0xff,
+		b: b / 0xff,
+	};
+};
+
+function Duotone( { id: duotoneId, darkColor, lightColor } ) {
+	const duotoneDark = hex2rgb( darkColor );
+	const duotoneLight = hex2rgb( lightColor );
+
+	return (
+		<SVG
+			xmlnsXlink="http://www.w3.org/1999/xlink"
+			viewBox="0 0 0 0"
+			width="0"
+			height="0"
+			focusable="false"
+			role="none"
+			style={ {
+				visibility: 'hidden',
+				position: 'absolute',
+				left: '-9999px',
+				overflow: 'hidden',
+			} }
+		>
+			<defs>
+				<filter id={ duotoneId }>
+					<feColorMatrix
+						type="matrix"
+						// prettier-ignore
+						values=".2989 .5870 .1140 0 0
+						        .2989 .5870 .1140 0 0
+						        .2989 .5870 .1140 0 0
+						        0 0 0 1 0"
+					/>
+					<feComponentTransfer colorInterpolationFilters="sRGB">
+						<feFuncR
+							type="table"
+							tableValues={ `${ duotoneDark.r } ${ duotoneLight.r }` }
+						/>
+						<feFuncG
+							type="table"
+							tableValues={ `${ duotoneDark.g } ${ duotoneLight.g }` }
+						/>
+						<feFuncB
+							type="table"
+							tableValues={ `${ duotoneDark.b } ${ duotoneLight.b }` }
+						/>
+					</feComponentTransfer>
+				</filter>
+			</defs>
+		</SVG>
+	);
+}
+
+export default Duotone;

blocks/duotone-filter/src/index.js

@@ -0,0 +1,132 @@
+/**
+ * WordPress dependencies
+ */
+import { InspectorControls, PanelColorSettings } from '@wordpress/block-editor';
+import { createHigherOrderComponent, useInstanceId } from '@wordpress/compose';
+import { useEffect } from '@wordpress/element';
+import { addFilter } from '@wordpress/hooks';
+import { __ } from '@wordpress/i18n';
+
+/**
+ * Internal dependencies
+ */
+import Duotone from './duotone';
+
+const SUPPORTED_BLOCKS = [ 'core/image', 'core/cover' ];
+
+export const isSupportedBlock = ( blockName ) =>
+	SUPPORTED_BLOCKS.includes( blockName );
+
+const withDuotoneAttributes = ( settings, blockName ) => {
+	if ( isSupportedBlock( blockName ) ) {
+		Object.assign( settings.attributes, {
+			duotoneId: {
+				type: 'string',
+			},
+			duotoneDark: {
+				type: 'string',
+			},
+			duotoneLight: {
+				type: 'string',
+			},
+		} );
+	}
+	return settings;
+};
+
+const withDuotoneEditorControls = createHigherOrderComponent(
+	( BlockEdit ) => ( props ) => {
+		const { name: blockName, attributes, setAttributes } = props;
+
+		if ( ! isSupportedBlock( blockName ) ) {
+			return <BlockEdit { ...props } />;
+		}
+
+		const instanceId = useInstanceId( BlockEdit );
+
+		useEffect( () => {
+			setAttributes( {
+				duotoneId: `a8c-duotone-filter-${ instanceId }`,
+			} );
+		}, [ instanceId ] );
+
+		return (
+			<>
+				<InspectorControls>
+					<PanelColorSettings
+						title={ __( 'Duotone', 'block-experiments' ) }
+						initialOpen
+						colorSettings={ [
+							{
+								label: __( 'Dark Color', 'block-experiments' ),
+								value: attributes.duotoneDark,
+								onChange: ( duotoneDark ) =>
+									setAttributes( { duotoneDark } ),
+							},
+							{
+								label: __( 'Light Color', 'block-experiments' ),
+								value: attributes.duotoneLight,
+								onChange: ( duotoneLight ) =>
+									setAttributes( { duotoneLight } ),
+							},
+						] }
+					/>
+				</InspectorControls>
+				{ attributes.duotoneDark &&
+				attributes.duotoneLight &&
+				attributes.duotoneId ? (
+					<>
+						<Duotone
+							id={ attributes.duotoneId }
+							darkColor={ attributes.duotoneDark }
+							lightColor={ attributes.duotoneLight }
+						/>
+						<div
+							style={ {
+								filter: `url( #${ attributes.duotoneId } )`,
+							} }
+						>
+							<BlockEdit { ...props } />
+						</div>
+					</>
+				) : (
+					<BlockEdit { ...props } />
+				) }
+			</>
+		);
+	},
+	'withDuotoneEditorControls'
+);
+
+function addDuotoneFilterStyle( props, block, attributes ) {
+	if (
+		! isSupportedBlock( block.name ) ||
+		! attributes.duotoneDark ||
+		! attributes.duotoneLight ||
+		! attributes.duotoneId
+	) {
+		return props;
+	}
+
+	const { style = {} } = props;
+
+	return { style: { ...style, filter: `url( #${ attributes.duotoneId } )` } };
+}
+
+export function registerBlock() {
+	addFilter(
+		'editor.BlockEdit',
+		'a8c/duotone-filter/with-editor-controls',
+		withDuotoneEditorControls
+	);
+	addFilter(
+		'blocks.registerBlockType',
+		'a8c/duotone-filter/add-attributes',
+		withDuotoneAttributes
+	);
+	addFilter(
+		'blocks.getSaveContent.extraProps',
+		'a8c/duotone-filter/add-filter-style',
+		addDuotoneFilterStyle
+	);
+}

src/index.js

@@ -23,6 +23,7 @@ setCategories( [
  * Load all our blocks
  */
 import * as bauhausCentenaryBlock from '../blocks/bauhaus-centenary/src';
+import * as duotoneFilter from '../blocks/duotone-filter/src';
 import * as eventBlock from '../blocks/event/src';
 import * as layoutGridBlock from '../blocks/layout-grid/src';
 import * as motionBackgroundBlock from '../blocks/motion-background/src';
@@ -31,6 +32,7 @@ import * as wavesBlock from '../blocks/waves/src';
 
 // Instantiate the blocks, adding them to our block category
 bauhausCentenaryBlock.registerBlock();
+duotoneFilter.registerBlock();
 eventBlock.registerBlock();
 layoutGridBlock.registerBlock();
 motionBackgroundBlock.registerBlock();