Add support for faded connectors

bin/generate-screenshots.js

@@ -81,9 +81,12 @@ function findSamples(content) {
 	 *  code: (
 	 *   'theme chunky\n' +
 	 *   'define ABC as A, DEF as B\n' +
+	 *   'A is red\n' +
+	 *   'B is blue\n' +
 	 *   'A -> B\n' +
-	 *   'B -> ]\n' +
-	 *   '] -> B\n' +
+	 *   'B -~ ]\n' +
+	 *   'divider space with height 0\n' +
+	 *   '] ~-> B\n' +
 	 *   'B -> A\n' +
 	 *   'terminators fade'
 	 *  ),

lib/sequence-diagram-web.js

@@ -598,6 +598,10 @@
 								'stroke-linejoin': 'miter',
 							},
 						},
+						'fade': {
+							short: 2,
+							size: 16,
+						},
 						'cross': {
 							short: 7,
 							radius: 3,
@@ -985,6 +989,10 @@
 								'stroke-linecap': 'round',
 							},
 						},
+						'fade': {
+							short: 3,
+							size: 12,
+						},
 						'cross': {
 							short: 10,
 							radius: 5,
@@ -2960,6 +2968,10 @@
 								'stroke-linejoin': 'miter',
 							},
 						},
+						'fade': {
+							short: 2,
+							size: 10,
+						},
 						'cross': {
 							short: 8,
 							radius: 4,
@@ -4424,6 +4436,7 @@
 				{tok: '', type: 0},
 				{tok: '<', type: 1},
 				{tok: '<<', type: 2},
+				{tok: '~', type: 3},
 			];
 			const mTypes = [
 				{tok: '-', type: 'solid'},
@@ -4434,19 +4447,27 @@
 				{tok: '', type: 0},
 				{tok: '>', type: 1},
 				{tok: '>>', type: 2},
-				{tok: 'x', type: 3},
+				{tok: '~', type: 3},
+				{tok: 'x', type: 4},
 			];
-			const arrows = (combine([lTypes, mTypes, rTypes])
-				.filter((arrow) => (arrow[0].type !== 0 || arrow[2].type !== 0))
-			);
 
 			const types = new Map();
 
-			arrows.forEach((arrow) => {
+			combine([lTypes, mTypes, rTypes]).forEach((arrow) => {
+				const [left, line, right] = arrow;
+				if(left.type === 0 && right.type === 0) {
+					// A line without arrows cannot be a connector
+					return;
+				}
+				if(left.type === 3 && line.type === 'wave' && right.type === 0) {
+					// ~~ could be fade-wave-none or none-wave-fade
+					// We allow only none-wave-fade to resolve this
+					return;
+				}
 				types.set(arrow.map((part) => part.tok).join(''), {
-					left: arrow[0].type,
-					line: arrow[1].type,
-					right: arrow[2].type,
+					left: left.type,
+					line: line.type,
+					right: right.type,
 				});
 			});
 
@@ -5776,6 +5797,18 @@
 		'fill': 'transparent',
 	};
 
+	const MASK_PAD = 5;
+
+	function applyMask(shape, maskShapes, env, bounds) {
+		if(!maskShapes.length) {
+			return;
+		}
+		const mask = env.svg.el('mask')
+			.attr('maskUnits', 'userSpaceOnUse')
+			.add(env.svg.box({'fill': '#FFFFFF'}, bounds), ...maskShapes);
+		shape.attr('mask', 'url(#' + env.addDef(mask) + ')');
+	}
+
 	class Arrowhead {
 		constructor(propName) {
 			this.propName = propName;
@@ -5800,9 +5833,9 @@
 			}
 		}
 
-		render(layer, theme, pt, dir) {
-			const config = this.getConfig(theme);
-			const short = this.short(theme);
+		render({layer}, env, pt, dir) {
+			const config = this.getConfig(env.theme);
+			const short = this.short(env.theme);
 			layer.add(config.render(config.attrs, {
 				dir,
 				height: config.height,
@@ -5834,13 +5867,58 @@
 		}
 	}
 
+	class Arrowfade {
+		getConfig(theme) {
+			return theme.connect.arrow.fade;
+		}
+
+		render({lineMask}, env, pt, dir) {
+			const config = this.getConfig(env.theme);
+			const {short, size} = config;
+			let fadeID = null;
+			const delta = MASK_PAD / (size + MASK_PAD * 2);
+			if(dir.dx >= 0) {
+				fadeID = env.addDef('arrowFadeL', () => env.svg.linearGradient({}, [
+					{'offset': delta * 100 + '%', 'stop-color': '#000000'},
+					{'offset': (100 - delta * 100) + '%', 'stop-color': '#FFFFFF'},
+				]));
+			} else {
+				fadeID = env.addDef('arrowFadeR', () => env.svg.linearGradient({}, [
+					{'offset': delta * 100 + '%', 'stop-color': '#FFFFFF'},
+					{'offset': (100 - delta * 100) + '%', 'stop-color': '#000000'},
+				]));
+			}
+			const p1 = {x: pt.x + dir.dx * short, y: pt.y + dir.dy * short};
+			const p2 = {x: p1.x + dir.dx * size, y: p1.y + dir.dy * size};
+			const box = env.svg.box({'fill': 'url(#' + fadeID + ')'}, {
+				height: Math.abs(p1.y - p2.y) + MASK_PAD * 2,
+				width: size + MASK_PAD * 2,
+				x: Math.min(p1.x, p2.x) - MASK_PAD,
+				y: Math.min(p1.y, p2.y) - MASK_PAD,
+			});
+			lineMask.push(box);
+		}
+
+		width(theme) {
+			return this.getConfig(theme).short;
+		}
+
+		height() {
+			return 0;
+		}
+
+		lineGap(theme) {
+			return this.getConfig(theme).short;
+		}
+	}
+
 	class Arrowcross {
 		getConfig(theme) {
 			return theme.connect.arrow.cross;
 		}
 
-		render(layer, theme, pt, dir) {
-			const config = this.getConfig(theme);
+		render({layer}, env, pt, dir) {
+			const config = this.getConfig(env.theme);
 			layer.add(config.render({
 				radius: config.radius,
 				x: pt.x + config.short * dir.dx,
@@ -5871,6 +5949,7 @@
 		},
 		new Arrowhead('single'),
 		new Arrowhead('double'),
+		new Arrowfade(),
 		new Arrowcross(),
 	];
 
@@ -5950,8 +6029,9 @@
 
 			const dx1 = lArrow.lineGap(env.theme, line);
 			const dx2 = rArrow.lineGap(env.theme, line);
+			const rad = env.theme.connect.loopbackRadius;
 			const rendered = line.renderRev({
-				rad: env.theme.connect.loopbackRadius,
+				rad,
 				x1: x1 + dx1,
 				x2: x2 + dx2,
 				xR,
@@ -5960,15 +6040,24 @@
 			});
 			clickable.add(rendered.shape);
 
-			lArrow.render(clickable, env.theme, {
+			const lineMask = [];
+
+			lArrow.render({layer: clickable, lineMask}, env, {
 				x: rendered.p1.x - dx1,
 				y: rendered.p1.y,
 			}, {dx: 1, dy: 0});
 
-			rArrow.render(clickable, env.theme, {
+			rArrow.render({layer: clickable, lineMask}, env, {
 				x: rendered.p2.x - dx2,
 				y: rendered.p2.y,
 			}, {dx: 1, dy: 0});
+
+			applyMask(rendered.shape, lineMask, env, {
+				height: y2 - y1 + MASK_PAD * 2,
+				width: xR + rad - Math.min(x1, x2) + MASK_PAD * 2,
+				x: Math.min(x1, x2) - MASK_PAD,
+				y: y1 - MASK_PAD,
+			});
 		}
 
 		renderSelfConnect({label, agentIDs, options}, env, from, yBegin) {
@@ -6066,8 +6155,20 @@
 			const p1 = {x: rendered.p1.x - d1 * dx, y: rendered.p1.y - d1 * dy};
 			const p2 = {x: rendered.p2.x + d2 * dx, y: rendered.p2.y + d2 * dy};
 
-			lArrow.render(clickable, env.theme, p1, {dx, dy});
-			rArrow.render(clickable, env.theme, p2, {dx: -dx, dy: -dy});
+			const lineMask = [];
+
+			lArrow.render({layer: clickable, lineMask}, env, p1, {dx, dy});
+			rArrow.render({layer: clickable, lineMask}, env, p2, {
+				dx: -dx,
+				dy: -dy,
+			});
+
+			applyMask(rendered.shape, lineMask, env, {
+				height: Math.abs(y2 - y1) + MASK_PAD * 2,
+				width: Math.abs(x2 - x1) + MASK_PAD * 2,
+				x: Math.min(x1, x2) - MASK_PAD,
+				y: Math.min(y1, y2) - MASK_PAD,
+			});
 
 			return {
 				lArrow,
@@ -9044,6 +9145,10 @@
 							}, PENCIL.normal),
 							render: this.renderArrowHead.bind(this),
 						},
+						'fade': {
+							short: 0,
+							size: 12,
+						},
 						'cross': {
 							short: 5,
 							radius: 3,

lib/sequence-diagram.js

@@ -598,6 +598,10 @@
 								'stroke-linejoin': 'miter',
 							},
 						},
+						'fade': {
+							short: 2,
+							size: 16,
+						},
 						'cross': {
 							short: 7,
 							radius: 3,
@@ -985,6 +989,10 @@
 								'stroke-linecap': 'round',
 							},
 						},
+						'fade': {
+							short: 3,
+							size: 12,
+						},
 						'cross': {
 							short: 10,
 							radius: 5,
@@ -2960,6 +2968,10 @@
 								'stroke-linejoin': 'miter',
 							},
 						},
+						'fade': {
+							short: 2,
+							size: 10,
+						},
 						'cross': {
 							short: 8,
 							radius: 4,
@@ -4424,6 +4436,7 @@
 				{tok: '', type: 0},
 				{tok: '<', type: 1},
 				{tok: '<<', type: 2},
+				{tok: '~', type: 3},
 			];
 			const mTypes = [
 				{tok: '-', type: 'solid'},
@@ -4434,19 +4447,27 @@
 				{tok: '', type: 0},
 				{tok: '>', type: 1},
 				{tok: '>>', type: 2},
-				{tok: 'x', type: 3},
+				{tok: '~', type: 3},
+				{tok: 'x', type: 4},
 			];
-			const arrows = (combine([lTypes, mTypes, rTypes])
-				.filter((arrow) => (arrow[0].type !== 0 || arrow[2].type !== 0))
-			);
 
 			const types = new Map();
 
-			arrows.forEach((arrow) => {
+			combine([lTypes, mTypes, rTypes]).forEach((arrow) => {
+				const [left, line, right] = arrow;
+				if(left.type === 0 && right.type === 0) {
+					// A line without arrows cannot be a connector
+					return;
+				}
+				if(left.type === 3 && line.type === 'wave' && right.type === 0) {
+					// ~~ could be fade-wave-none or none-wave-fade
+					// We allow only none-wave-fade to resolve this
+					return;
+				}
 				types.set(arrow.map((part) => part.tok).join(''), {
-					left: arrow[0].type,
-					line: arrow[1].type,
-					right: arrow[2].type,
+					left: left.type,
+					line: line.type,
+					right: right.type,
 				});
 			});
 
@@ -5776,6 +5797,18 @@
 		'fill': 'transparent',
 	};
 
+	const MASK_PAD = 5;
+
+	function applyMask(shape, maskShapes, env, bounds) {
+		if(!maskShapes.length) {
+			return;
+		}
+		const mask = env.svg.el('mask')
+			.attr('maskUnits', 'userSpaceOnUse')
+			.add(env.svg.box({'fill': '#FFFFFF'}, bounds), ...maskShapes);
+		shape.attr('mask', 'url(#' + env.addDef(mask) + ')');
+	}
+
 	class Arrowhead {
 		constructor(propName) {
 			this.propName = propName;
@@ -5800,9 +5833,9 @@
 			}
 		}
 
-		render(layer, theme, pt, dir) {
-			const config = this.getConfig(theme);
-			const short = this.short(theme);
+		render({layer}, env, pt, dir) {
+			const config = this.getConfig(env.theme);
+			const short = this.short(env.theme);
 			layer.add(config.render(config.attrs, {
 				dir,
 				height: config.height,
@@ -5834,13 +5867,58 @@
 		}
 	}
 
+	class Arrowfade {
+		getConfig(theme) {
+			return theme.connect.arrow.fade;
+		}
+
+		render({lineMask}, env, pt, dir) {
+			const config = this.getConfig(env.theme);
+			const {short, size} = config;
+			let fadeID = null;
+			const delta = MASK_PAD / (size + MASK_PAD * 2);
+			if(dir.dx >= 0) {
+				fadeID = env.addDef('arrowFadeL', () => env.svg.linearGradient({}, [
+					{'offset': delta * 100 + '%', 'stop-color': '#000000'},
+					{'offset': (100 - delta * 100) + '%', 'stop-color': '#FFFFFF'},
+				]));
+			} else {
+				fadeID = env.addDef('arrowFadeR', () => env.svg.linearGradient({}, [
+					{'offset': delta * 100 + '%', 'stop-color': '#FFFFFF'},
+					{'offset': (100 - delta * 100) + '%', 'stop-color': '#000000'},
+				]));
+			}
+			const p1 = {x: pt.x + dir.dx * short, y: pt.y + dir.dy * short};
+			const p2 = {x: p1.x + dir.dx * size, y: p1.y + dir.dy * size};
+			const box = env.svg.box({'fill': 'url(#' + fadeID + ')'}, {
+				height: Math.abs(p1.y - p2.y) + MASK_PAD * 2,
+				width: size + MASK_PAD * 2,
+				x: Math.min(p1.x, p2.x) - MASK_PAD,
+				y: Math.min(p1.y, p2.y) - MASK_PAD,
+			});
+			lineMask.push(box);
+		}
+
+		width(theme) {
+			return this.getConfig(theme).short;
+		}
+
+		height() {
+			return 0;
+		}
+
+		lineGap(theme) {
+			return this.getConfig(theme).short;
+		}
+	}
+
 	class Arrowcross {
 		getConfig(theme) {
 			return theme.connect.arrow.cross;
 		}
 
-		render(layer, theme, pt, dir) {
-			const config = this.getConfig(theme);
+		render({layer}, env, pt, dir) {
+			const config = this.getConfig(env.theme);
 			layer.add(config.render({
 				radius: config.radius,
 				x: pt.x + config.short * dir.dx,
@@ -5871,6 +5949,7 @@
 		},
 		new Arrowhead('single'),
 		new Arrowhead('double'),
+		new Arrowfade(),
 		new Arrowcross(),
 	];
 
@@ -5950,8 +6029,9 @@
 
 			const dx1 = lArrow.lineGap(env.theme, line);
 			const dx2 = rArrow.lineGap(env.theme, line);
+			const rad = env.theme.connect.loopbackRadius;
 			const rendered = line.renderRev({
-				rad: env.theme.connect.loopbackRadius,
+				rad,
 				x1: x1 + dx1,
 				x2: x2 + dx2,
 				xR,
@@ -5960,15 +6040,24 @@
 			});
 			clickable.add(rendered.shape);
 
-			lArrow.render(clickable, env.theme, {
+			const lineMask = [];
+
+			lArrow.render({layer: clickable, lineMask}, env, {
 				x: rendered.p1.x - dx1,
 				y: rendered.p1.y,
 			}, {dx: 1, dy: 0});
 
-			rArrow.render(clickable, env.theme, {
+			rArrow.render({layer: clickable, lineMask}, env, {
 				x: rendered.p2.x - dx2,
 				y: rendered.p2.y,
 			}, {dx: 1, dy: 0});
+
+			applyMask(rendered.shape, lineMask, env, {
+				height: y2 - y1 + MASK_PAD * 2,
+				width: xR + rad - Math.min(x1, x2) + MASK_PAD * 2,
+				x: Math.min(x1, x2) - MASK_PAD,
+				y: y1 - MASK_PAD,
+			});
 		}
 
 		renderSelfConnect({label, agentIDs, options}, env, from, yBegin) {
@@ -6066,8 +6155,20 @@
 			const p1 = {x: rendered.p1.x - d1 * dx, y: rendered.p1.y - d1 * dy};
 			const p2 = {x: rendered.p2.x + d2 * dx, y: rendered.p2.y + d2 * dy};
 
-			lArrow.render(clickable, env.theme, p1, {dx, dy});
-			rArrow.render(clickable, env.theme, p2, {dx: -dx, dy: -dy});
+			const lineMask = [];
+
+			lArrow.render({layer: clickable, lineMask}, env, p1, {dx, dy});
+			rArrow.render({layer: clickable, lineMask}, env, p2, {
+				dx: -dx,
+				dy: -dy,
+			});
+
+			applyMask(rendered.shape, lineMask, env, {
+				height: Math.abs(y2 - y1) + MASK_PAD * 2,
+				width: Math.abs(x2 - x1) + MASK_PAD * 2,
+				x: Math.min(x1, x2) - MASK_PAD,
+				y: Math.min(y1, y2) - MASK_PAD,
+			});
 
 			return {
 				lArrow,
@@ -9044,6 +9145,10 @@
 							}, PENCIL.normal),
 							render: this.renderArrowHead.bind(this),
 						},
+						'fade': {
+							short: 0,
+							size: 12,
+						},
 						'cross': {
 							short: 5,
 							radius: 3,

scripts/sequence/parser/Parser.mjs

@@ -42,6 +42,7 @@ const CONNECT = {
 			{tok: '', type: 0},
 			{tok: '<', type: 1},
 			{tok: '<<', type: 2},
+			{tok: '~', type: 3},
 		];
 		const mTypes = [
 			{tok: '-', type: 'solid'},
@@ -52,19 +53,27 @@ const CONNECT = {
 			{tok: '', type: 0},
 			{tok: '>', type: 1},
 			{tok: '>>', type: 2},
-			{tok: 'x', type: 3},
+			{tok: '~', type: 3},
+			{tok: 'x', type: 4},
 		];
-		const arrows = (combine([lTypes, mTypes, rTypes])
-			.filter((arrow) => (arrow[0].type !== 0 || arrow[2].type !== 0))
-		);
 
 		const types = new Map();
 
-		arrows.forEach((arrow) => {
+		combine([lTypes, mTypes, rTypes]).forEach((arrow) => {
+			const [left, line, right] = arrow;
+			if(left.type === 0 && right.type === 0) {
+				// A line without arrows cannot be a connector
+				return;
+			}
+			if(left.type === 3 && line.type === 'wave' && right.type === 0) {
+				// ~~ could be fade-wave-none or none-wave-fade
+				// We allow only none-wave-fade to resolve this
+				return;
+			}
 			types.set(arrow.map((part) => part.tok).join(''), {
-				left: arrow[0].type,
-				line: arrow[1].type,
-				right: arrow[2].type,
+				left: left.type,
+				line: line.type,
+				right: right.type,
 			});
 		});
 

scripts/sequence/parser/Parser_spec.mjs

@@ -453,31 +453,62 @@ describe('Sequence Parser', () => {
 			const parsed = parser.parse(
 				'A->B\n' +
 				'A->>B\n' +
+				'A-~B\n' +
+				'A-xB\n' +
 				'A<-B\n' +
 				'A<->B\n' +
 				'A<->>B\n' +
+				'A<-~B\n' +
+				'A<-xB\n' +
 				'A<<-B\n' +
 				'A<<->B\n' +
 				'A<<->>B\n' +
-				'A-xB\n' +
+				'A<<-~B\n' +
+				'A<<-xB\n' +
+				'A~-B\n' +
+				'A~->B\n' +
+				'A~->>B\n' +
+				'A~-~B\n' +
+				'A~-xB\n' +
+
 				'A-->B\n' +
 				'A-->>B\n' +
+				'A--~B\n' +
+				'A--xB\n' +
 				'A<--B\n' +
 				'A<-->B\n' +
 				'A<-->>B\n' +
+				'A<--~B\n' +
+				'A<--xB\n' +
 				'A<<--B\n' +
 				'A<<-->B\n' +
 				'A<<-->>B\n' +
-				'A--xB\n' +
+				'A<<--~B\n' +
+				'A<<--xB\n' +
+				'A~--B\n' +
+				'A~-->B\n' +
+				'A~-->>B\n' +
+				'A~--~B\n' +
+				'A~--xB\n' +
+
 				'A~>B\n' +
 				'A~>>B\n' +
+				'A~~B\n' +
+				'A~xB\n' +
 				'A<~B\n' +
 				'A<~>B\n' +
 				'A<~>>B\n' +
+				'A<~~B\n' +
+				'A<~xB\n' +
 				'A<<~B\n' +
 				'A<<~>B\n' +
 				'A<<~>>B\n' +
-				'A~xB\n'
+				'A<<~~B\n' +
+				'A<<~xB\n' +
+				'A~~>B\n' +
+				'A~~>>B\n' +
+				'A~~~B\n' +
+				'A~~xB\n'
 			);
 
 			expect(parsed.stages).toEqual([
@@ -488,31 +519,62 @@ describe('Sequence Parser', () => {
 					right: 1,
 				}),
 				PARSED.connect(['A', 'B'], {left: 0, line: 'solid', right: 2}),
+				PARSED.connect(['A', 'B'], {left: 0, line: 'solid', right: 3}),
+				PARSED.connect(['A', 'B'], {left: 0, line: 'solid', right: 4}),
 				PARSED.connect(['A', 'B'], {left: 1, line: 'solid', right: 0}),
 				PARSED.connect(['A', 'B'], {left: 1, line: 'solid', right: 1}),
 				PARSED.connect(['A', 'B'], {left: 1, line: 'solid', right: 2}),
+				PARSED.connect(['A', 'B'], {left: 1, line: 'solid', right: 3}),
+				PARSED.connect(['A', 'B'], {left: 1, line: 'solid', right: 4}),
 				PARSED.connect(['A', 'B'], {left: 2, line: 'solid', right: 0}),
 				PARSED.connect(['A', 'B'], {left: 2, line: 'solid', right: 1}),
 				PARSED.connect(['A', 'B'], {left: 2, line: 'solid', right: 2}),
-				PARSED.connect(['A', 'B'], {left: 0, line: 'solid', right: 3}),
+				PARSED.connect(['A', 'B'], {left: 2, line: 'solid', right: 3}),
+				PARSED.connect(['A', 'B'], {left: 2, line: 'solid', right: 4}),
+				PARSED.connect(['A', 'B'], {left: 3, line: 'solid', right: 0}),
+				PARSED.connect(['A', 'B'], {left: 3, line: 'solid', right: 1}),
+				PARSED.connect(['A', 'B'], {left: 3, line: 'solid', right: 2}),
+				PARSED.connect(['A', 'B'], {left: 3, line: 'solid', right: 3}),
+				PARSED.connect(['A', 'B'], {left: 3, line: 'solid', right: 4}),
+
 				PARSED.connect(['A', 'B'], {left: 0, line: 'dash', right: 1}),
 				PARSED.connect(['A', 'B'], {left: 0, line: 'dash', right: 2}),
+				PARSED.connect(['A', 'B'], {left: 0, line: 'dash', right: 3}),
+				PARSED.connect(['A', 'B'], {left: 0, line: 'dash', right: 4}),
 				PARSED.connect(['A', 'B'], {left: 1, line: 'dash', right: 0}),
 				PARSED.connect(['A', 'B'], {left: 1, line: 'dash', right: 1}),
 				PARSED.connect(['A', 'B'], {left: 1, line: 'dash', right: 2}),
+				PARSED.connect(['A', 'B'], {left: 1, line: 'dash', right: 3}),
+				PARSED.connect(['A', 'B'], {left: 1, line: 'dash', right: 4}),
 				PARSED.connect(['A', 'B'], {left: 2, line: 'dash', right: 0}),
 				PARSED.connect(['A', 'B'], {left: 2, line: 'dash', right: 1}),
 				PARSED.connect(['A', 'B'], {left: 2, line: 'dash', right: 2}),
-				PARSED.connect(['A', 'B'], {left: 0, line: 'dash', right: 3}),
+				PARSED.connect(['A', 'B'], {left: 2, line: 'dash', right: 3}),
+				PARSED.connect(['A', 'B'], {left: 2, line: 'dash', right: 4}),
+				PARSED.connect(['A', 'B'], {left: 3, line: 'dash', right: 0}),
+				PARSED.connect(['A', 'B'], {left: 3, line: 'dash', right: 1}),
+				PARSED.connect(['A', 'B'], {left: 3, line: 'dash', right: 2}),
+				PARSED.connect(['A', 'B'], {left: 3, line: 'dash', right: 3}),
+				PARSED.connect(['A', 'B'], {left: 3, line: 'dash', right: 4}),
+
 				PARSED.connect(['A', 'B'], {left: 0, line: 'wave', right: 1}),
 				PARSED.connect(['A', 'B'], {left: 0, line: 'wave', right: 2}),
+				PARSED.connect(['A', 'B'], {left: 0, line: 'wave', right: 3}),
+				PARSED.connect(['A', 'B'], {left: 0, line: 'wave', right: 4}),
 				PARSED.connect(['A', 'B'], {left: 1, line: 'wave', right: 0}),
 				PARSED.connect(['A', 'B'], {left: 1, line: 'wave', right: 1}),
 				PARSED.connect(['A', 'B'], {left: 1, line: 'wave', right: 2}),
+				PARSED.connect(['A', 'B'], {left: 1, line: 'wave', right: 3}),
+				PARSED.connect(['A', 'B'], {left: 1, line: 'wave', right: 4}),
 				PARSED.connect(['A', 'B'], {left: 2, line: 'wave', right: 0}),
 				PARSED.connect(['A', 'B'], {left: 2, line: 'wave', right: 1}),
 				PARSED.connect(['A', 'B'], {left: 2, line: 'wave', right: 2}),
-				PARSED.connect(['A', 'B'], {left: 0, line: 'wave', right: 3}),
+				PARSED.connect(['A', 'B'], {left: 2, line: 'wave', right: 3}),
+				PARSED.connect(['A', 'B'], {left: 2, line: 'wave', right: 4}),
+				PARSED.connect(['A', 'B'], {left: 3, line: 'wave', right: 1}),
+				PARSED.connect(['A', 'B'], {left: 3, line: 'wave', right: 2}),
+				PARSED.connect(['A', 'B'], {left: 3, line: 'wave', right: 3}),
+				PARSED.connect(['A', 'B'], {left: 3, line: 'wave', right: 4}),
 			]);
 		});
 

scripts/sequence/renderer/components/Connect.mjs

@@ -6,6 +6,18 @@ const OUTLINE_ATTRS = {
 	'fill': 'transparent',
 };
 
+const MASK_PAD = 5;
+
+function applyMask(shape, maskShapes, env, bounds) {
+	if(!maskShapes.length) {
+		return;
+	}
+	const mask = env.svg.el('mask')
+		.attr('maskUnits', 'userSpaceOnUse')
+		.add(env.svg.box({'fill': '#FFFFFF'}, bounds), ...maskShapes);
+	shape.attr('mask', 'url(#' + env.addDef(mask) + ')');
+}
+
 class Arrowhead {
 	constructor(propName) {
 		this.propName = propName;
@@ -30,9 +42,9 @@ class Arrowhead {
 		}
 	}
 
-	render(layer, theme, pt, dir) {
-		const config = this.getConfig(theme);
-		const short = this.short(theme);
+	render({layer}, env, pt, dir) {
+		const config = this.getConfig(env.theme);
+		const short = this.short(env.theme);
 		layer.add(config.render(config.attrs, {
 			dir,
 			height: config.height,
@@ -64,13 +76,58 @@ class Arrowhead {
 	}
 }
 
+class Arrowfade {
+	getConfig(theme) {
+		return theme.connect.arrow.fade;
+	}
+
+	render({lineMask}, env, pt, dir) {
+		const config = this.getConfig(env.theme);
+		const {short, size} = config;
+		let fadeID = null;
+		const delta = MASK_PAD / (size + MASK_PAD * 2);
+		if(dir.dx >= 0) {
+			fadeID = env.addDef('arrowFadeL', () => env.svg.linearGradient({}, [
+				{'offset': delta * 100 + '%', 'stop-color': '#000000'},
+				{'offset': (100 - delta * 100) + '%', 'stop-color': '#FFFFFF'},
+			]));
+		} else {
+			fadeID = env.addDef('arrowFadeR', () => env.svg.linearGradient({}, [
+				{'offset': delta * 100 + '%', 'stop-color': '#FFFFFF'},
+				{'offset': (100 - delta * 100) + '%', 'stop-color': '#000000'},
+			]));
+		}
+		const p1 = {x: pt.x + dir.dx * short, y: pt.y + dir.dy * short};
+		const p2 = {x: p1.x + dir.dx * size, y: p1.y + dir.dy * size};
+		const box = env.svg.box({'fill': 'url(#' + fadeID + ')'}, {
+			height: Math.abs(p1.y - p2.y) + MASK_PAD * 2,
+			width: size + MASK_PAD * 2,
+			x: Math.min(p1.x, p2.x) - MASK_PAD,
+			y: Math.min(p1.y, p2.y) - MASK_PAD,
+		});
+		lineMask.push(box);
+	}
+
+	width(theme) {
+		return this.getConfig(theme).short;
+	}
+
+	height() {
+		return 0;
+	}
+
+	lineGap(theme) {
+		return this.getConfig(theme).short;
+	}
+}
+
 class Arrowcross {
 	getConfig(theme) {
 		return theme.connect.arrow.cross;
 	}
 
-	render(layer, theme, pt, dir) {
-		const config = this.getConfig(theme);
+	render({layer}, env, pt, dir) {
+		const config = this.getConfig(env.theme);
 		layer.add(config.render({
 			radius: config.radius,
 			x: pt.x + config.short * dir.dx,
@@ -101,6 +158,7 @@ const ARROWHEADS = [
 	},
 	new Arrowhead('single'),
 	new Arrowhead('double'),
+	new Arrowfade(),
 	new Arrowcross(),
 ];
 
@@ -180,8 +238,9 @@ export class Connect extends BaseComponent {
 
 		const dx1 = lArrow.lineGap(env.theme, line);
 		const dx2 = rArrow.lineGap(env.theme, line);
+		const rad = env.theme.connect.loopbackRadius;
 		const rendered = line.renderRev({
-			rad: env.theme.connect.loopbackRadius,
+			rad,
 			x1: x1 + dx1,
 			x2: x2 + dx2,
 			xR,
@@ -190,15 +249,24 @@ export class Connect extends BaseComponent {
 		});
 		clickable.add(rendered.shape);
 
-		lArrow.render(clickable, env.theme, {
+		const lineMask = [];
+
+		lArrow.render({layer: clickable, lineMask}, env, {
 			x: rendered.p1.x - dx1,
 			y: rendered.p1.y,
 		}, {dx: 1, dy: 0});
 
-		rArrow.render(clickable, env.theme, {
+		rArrow.render({layer: clickable, lineMask}, env, {
 			x: rendered.p2.x - dx2,
 			y: rendered.p2.y,
 		}, {dx: 1, dy: 0});
+
+		applyMask(rendered.shape, lineMask, env, {
+			height: y2 - y1 + MASK_PAD * 2,
+			width: xR + rad - Math.min(x1, x2) + MASK_PAD * 2,
+			x: Math.min(x1, x2) - MASK_PAD,
+			y: y1 - MASK_PAD,
+		});
 	}
 
 	renderSelfConnect({label, agentIDs, options}, env, from, yBegin) {
@@ -296,8 +364,20 @@ export class Connect extends BaseComponent {
 		const p1 = {x: rendered.p1.x - d1 * dx, y: rendered.p1.y - d1 * dy};
 		const p2 = {x: rendered.p2.x + d2 * dx, y: rendered.p2.y + d2 * dy};
 
-		lArrow.render(clickable, env.theme, p1, {dx, dy});
-		rArrow.render(clickable, env.theme, p2, {dx: -dx, dy: -dy});
+		const lineMask = [];
+
+		lArrow.render({layer: clickable, lineMask}, env, p1, {dx, dy});
+		rArrow.render({layer: clickable, lineMask}, env, p2, {
+			dx: -dx,
+			dy: -dy,
+		});
+
+		applyMask(rendered.shape, lineMask, env, {
+			height: Math.abs(y2 - y1) + MASK_PAD * 2,
+			width: Math.abs(x2 - x1) + MASK_PAD * 2,
+			x: Math.min(x1, x2) - MASK_PAD,
+			y: Math.min(y1, y2) - MASK_PAD,
+		});
 
 		return {
 			lArrow,

scripts/sequence/themes/Basic.mjs

@@ -170,6 +170,10 @@ export default class BasicTheme extends BaseTheme {
 							'stroke-linejoin': 'miter',
 						},
 					},
+					'fade': {
+						short: 2,
+						size: 16,
+					},
 					'cross': {
 						short: 7,
 						radius: 3,

scripts/sequence/themes/Chunky.mjs

@@ -179,6 +179,10 @@ export default class ChunkyTheme extends BaseTheme {
 							'stroke-linecap': 'round',
 						},
 					},
+					'fade': {
+						short: 3,
+						size: 12,
+					},
 					'cross': {
 						short: 10,
 						radius: 5,

scripts/sequence/themes/Monospace.mjs

@@ -170,6 +170,10 @@ export default class MonospaceTheme extends BaseTheme {
 							'stroke-linejoin': 'miter',
 						},
 					},
+					'fade': {
+						short: 2,
+						size: 10,
+					},
 					'cross': {
 						short: 8,
 						radius: 4,

scripts/sequence/themes/Sketch.mjs

@@ -201,6 +201,10 @@ export default class SketchTheme extends BaseTheme {
 						}, PENCIL.normal),
 						render: this.renderArrowHead.bind(this),
 					},
+					'fade': {
+						short: 0,
+						size: 12,
+					},
 					'cross': {
 						short: 5,
 						radius: 3,

spec/images/list.mjs

@@ -1,14 +1,15 @@
 export default [
-	'Connect.svg',
-	'SelfConnect.svg',
-	'Divider.svg',
-	'DividerMasking.svg',
+	'AgentOptions.svg',
 	'Asynchronous.svg',
 	'Block.svg',
 	'CollapsedBlocks.svg',
+	'Connect.svg',
+	'Divider.svg',
+	'DividerMasking.svg',
+	'Fade.svg',
+	'Markdown.svg',
+	'Parallel.svg',
 	'Reference.svg',
 	'ReferenceLayering.svg',
-	'Markdown.svg',
-	'AgentOptions.svg',
-	'Parallel.svg',
+	'SelfConnect.svg',
 ];

web/lib/editor.js

@@ -200,6 +200,10 @@
 			code: '[ -> {Agent1}: {Message1}\n{Agent1} -> ]: {Message2}',
 			title: 'Arrows to/from the sides',
 		},
+		{
+			code: '{Agent1} -~ ]: {Message1}\n{Agent1} <-~ ]: {Message2}',
+			title: 'Fading arrows',
+		},
 		{
 			code: 'text right: {Message}',
 			preview: (

web/scripts/interface/ComponentsLibrary.mjs

@@ -197,6 +197,10 @@ export default [
 		code: '[ -> {Agent1}: {Message1}\n{Agent1} -> ]: {Message2}',
 		title: 'Arrows to/from the sides',
 	},
+	{
+		code: '{Agent1} -~ ]: {Message1}\n{Agent1} <-~ ]: {Message2}',
+		title: 'Fading arrows',
+	},
 	{
 		code: 'text right: {Message}',
 		preview: (