Reduce number of forced reflows when rendering

lib/sequence-diagram.js

@@ -3387,13 +3387,17 @@ define('svg/SVGUtilities',[],() => {
 		return document.createTextNode(text);
 	}
 
-	function make(type, attrs = {}, children = []) {
+	function setAttributes(target, attrs) {
-		const o = document.createElementNS(NS, type);
 		for(const k in attrs) {
 			if(attrs.hasOwnProperty(k)) {
-				o.setAttribute(k, attrs[k]);
+				target.setAttribute(k, attrs[k]);
 			}
 		}
+	}
+
+	function make(type, attrs = {}, children = []) {
+		const o = document.createElementNS(NS, type);
+		setAttributes(o, attrs);
 		for(const c of children) {
 			o.appendChild(c);
 		}
@@ -3417,6 +3421,7 @@ define('svg/SVGUtilities',[],() => {
 		makeText,
 		make,
 		makeContainer,
+		setAttributes,
 		empty,
 	};
 });
@@ -3461,6 +3466,27 @@ define('svg/SVGTextBlock',['./SVGUtilities'], (svg) => {
 		});
 	}
 
+	function measureLine(tester, line) {
+		if(!line.length) {
+			return 0;
+		}
+
+		const labelKey = JSON.stringify(line);
+		const knownWidth = tester.widths.get(labelKey);
+		if(knownWidth !== undefined) {
+			return knownWidth;
+		}
+
+		// getComputedTextLength forces a reflow, so only call it if nothing
+		// else can tell us the length
+
+		svg.empty(tester.node);
+		populateSvgTextLine(tester.node, line);
+		const width = tester.node.getComputedTextLength();
+		tester.widths.set(labelKey, width);
+		return width;
+	}
+
 	const EMPTY = [];
 
 	class SVGTextBlock {
@@ -3472,8 +3498,6 @@ define('svg/SVGTextBlock',['./SVGUtilities'], (svg) => {
 				x: 0,
 				y: 0,
 			};
-			this.width = 0;
-			this.height = 0;
 			this.lines = [];
 			this.set(initialState);
 		}
@@ -3499,8 +3523,6 @@ define('svg/SVGTextBlock',['./SVGUtilities'], (svg) => {
 
 		_reset() {
 			this._rebuildLines(0);
-			this.width = 0;
-			this.height = 0;
 		}
 
 		_renderText() {
@@ -3516,7 +3538,6 @@ define('svg/SVGTextBlock',['./SVGUtilities'], (svg) => {
 
 			this._rebuildLines(formatted.length);
 
-			let maxWidth = 0;
 			this.lines.forEach((ln, i) => {
 				const id = JSON.stringify(formatted[i]);
 				if(id !== ln.latest) {
@@ -3524,9 +3545,7 @@ define('svg/SVGTextBlock',['./SVGUtilities'], (svg) => {
 					populateSvgTextLine(ln.node, formatted[i]);
 					ln.latest = id;
 				}
-				maxWidth = Math.max(maxWidth, ln.node.getComputedTextLength());
 			});
-			this.width = maxWidth;
 		}
 
 		_updateX() {
@@ -3540,7 +3559,6 @@ define('svg/SVGTextBlock',['./SVGUtilities'], (svg) => {
 			this.lines.forEach(({node}, i) => {
 				node.setAttribute('y', this.state.y + i * lineHeight + size);
 			});
-			this.height = lineHeight * this.lines.length;
 		}
 
 		firstLine() {
@@ -3587,47 +3605,62 @@ define('svg/SVGTextBlock',['./SVGUtilities'], (svg) => {
 			this.cache = new Map();
 		}
 
-		measure(attrs, formatted) {
+		_measureHeight({attrs, formatted}) {
-			if(!formatted || !formatted.length) {
+			return formatted.length * fontDetails(attrs).lineHeight;
-				return {width: 0, height: 0};
-			}
-			if(!Array.isArray(formatted)) {
-				throw new Error('Invalid formatted text: ' + formatted);
 		}
 
-			let tester = this.cache.get(attrs);
+		_measureWidth({attrs, formatted}) {
+			if(!formatted.length) {
+				return 0;
+			}
+
+			const attrKey = JSON.stringify(attrs);
+			let tester = this.cache.get(attrKey);
 			if(!tester) {
-				tester = svg.make('text', attrs);
+				const node = svg.make('text', attrs);
-				this.testers.appendChild(tester);
+				this.testers.appendChild(node);
-				this.cache.set(attrs, tester);
+				tester = {
+					node,
+					widths: new Map(),
+				};
+				this.cache.set(attrKey, tester);
 			}
 
 			if(!this.testers.parentNode) {
 				this.container.appendChild(this.testers);
 			}
 
-			let width = 0;
+			return (formatted
-			formatted.forEach((line) => {
+				.map((line) => measureLine(tester, line))
-				svg.empty(tester);
+				.reduce((a, b) => Math.max(a, b), 0)
-				populateSvgTextLine(tester, line);
+			);
-				width = Math.max(width, tester.getComputedTextLength());
+		}
-			});
 
+		_getMeasurementOpts(attrs, formatted) {
+			if(!formatted) {
+				if(typeof attrs === 'object' && attrs.state) {
+					formatted = attrs.state.formatted || [];
+					attrs = attrs.state.attrs;
+				} else {
+					formatted = [];
+				}
+			} else if(!Array.isArray(formatted)) {
+				throw new Error('Invalid formatted text: ' + formatted);
+			}
+			return {attrs, formatted};
+		}
+
+		measure(attrs, formatted) {
+			const opts = this._getMeasurementOpts(attrs, formatted);
 			return {
-				width,
+				width: this._measureWidth(opts),
-				height: formatted.length * fontDetails(attrs).lineHeight,
+				height: this._measureHeight(opts),
 			};
 		}
 
 		measureHeight(attrs, formatted) {
-			if(!formatted) {
+			const opts = this._getMeasurementOpts(attrs, formatted);
-				return 0;
+			return this._measureHeight(opts);
-			}
-			if(!Array.isArray(formatted)) {
-				throw new Error('Invalid formatted text: ' + formatted);
-			}
-
-			return formatted.length * fontDetails(attrs).lineHeight;
 		}
 
 		resetCache() {
@@ -3838,6 +3871,7 @@ define('svg/SVGShapes',[
 		labelLayer,
 		boxRenderer = null,
 		SVGTextBlockClass = SVGTextBlock,
+		textSizer,
 	}) {
 		if(!formatted || !formatted.length) {
 			return {width: 0, height: 0, label: null, box: null};
@@ -3852,20 +3886,21 @@ define('svg/SVGShapes',[
 			y: y + padding.top,
 		});
 
-		const width = (label.width + padding.left + padding.right);
+		const size = textSizer.measure(label);
-		const height = (label.height + padding.top + padding.bottom);
+		const width = (size.width + padding.left + padding.right);
+		const height = (size.height + padding.top + padding.bottom);
 
 		let box = null;
 		if(boxRenderer) {
 			box = boxRenderer({
-				'x': anchorX - label.width * shift - padding.left,
+				'x': anchorX - size.width * shift - padding.left,
 				'y': y,
 				'width': width,
 				'height': height,
 			});
 		} else {
 			box = renderBox(boxAttrs, {
-				'x': anchorX - label.width * shift - padding.left,
+				'x': anchorX - size.width * shift - padding.left,
 				'y': y,
 				'width': width,
 				'height': height,
@@ -4064,6 +4099,7 @@ define('sequence/components/Block',[
 				boxLayer: blockInfo.hold,
 				labelLayer: clickable,
 				SVGTextBlockClass: env.SVGTextBlockClass,
+				textSizer: env.textSizer,
 			});
 
 			const labelRender = SVGShapes.renderBoxedText(label, {
@@ -4075,6 +4111,7 @@ define('sequence/components/Block',[
 				boxLayer: env.lineMaskLayer,
 				labelLayer: clickable,
 				SVGTextBlockClass: env.SVGTextBlockClass,
+				textSizer: env.textSizer,
 			});
 
 			const labelHeight = Math.max(
@@ -4434,6 +4471,7 @@ define('sequence/components/AgentCap',[
 				boxLayer: clickable,
 				labelLayer: clickable,
 				SVGTextBlockClass: env.SVGTextBlockClass,
+				textSizer: env.textSizer,
 			});
 			clickable.insertBefore(svg.make('rect', {
 				'x': x - text.width / 2,
@@ -5003,6 +5041,7 @@ define('sequence/components/Connect',[
 				boxLayer: env.lineMaskLayer,
 				labelLayer: clickable,
 				SVGTextBlockClass: env.SVGTextBlockClass,
+				textSizer: env.textSizer,
 			});
 			const labelW = (label ? (
 				renderedText.width +
@@ -5129,6 +5168,7 @@ define('sequence/components/Connect',[
 				boxLayer: env.lineMaskLayer,
 				labelLayer,
 				SVGTextBlockClass: env.SVGTextBlockClass,
+				textSizer: env.textSizer,
 			});
 		}
 
@@ -5348,15 +5388,16 @@ define('sequence/components/Note',['./BaseComponent', 'svg/SVGUtilities'], (Base
 				formatted: label,
 				y,
 			});
+			const size = env.textSizer.measure(labelNode);
 
 			const fullW = (
-				labelNode.width +
+				size.width +
 				config.padding.left +
 				config.padding.right
 			);
 			const fullH = (
 				config.padding.top +
-				labelNode.height +
+				size.height +
 				config.padding.bottom
 			);
 			if(x0 === null && xMid !== null) {
@@ -5638,6 +5679,7 @@ define('sequence/components/Divider',[
 					boxLayer: env.fullMaskLayer,
 					labelLayer: clickable,
 					SVGTextBlockClass: env.SVGTextBlockClass,
+					textSizer: env.textSizer,
 				});
 				labelWidth = boxed.width;
 			}
@@ -6171,12 +6213,13 @@ define('sequence/Renderer',[
 
 		updateBounds(stagesHeight) {
 			const cx = (this.minX + this.maxX) / 2;
-			const titleY = ((this.title.height > 0) ?
+			const titleSize = this.sizer.measure(this.title);
-				(-this.theme.titleMargin - this.title.height) : 0
+			const titleY = ((titleSize.height > 0) ?
+				(-this.theme.titleMargin - titleSize.height) : 0
 			);
 			this.title.set({x: cx, y: titleY});
 
-			const halfTitleWidth = this.title.width / 2;
+			const halfTitleWidth = titleSize.width / 2;
 			const margin = this.theme.outerMargin;
 			const x0 = Math.min(this.minX, cx - halfTitleWidth) - margin;
 			const x1 = Math.max(this.maxX, cx + halfTitleWidth) + margin;
@@ -6186,15 +6229,15 @@ define('sequence/Renderer',[
 			this.width = x1 - x0;
 			this.height = y1 - y0;
 
-			this.fullMaskReveal.setAttribute('x', x0);
+			const fullSize = {
-			this.fullMaskReveal.setAttribute('y', y0);
+				'x': x0,
-			this.fullMaskReveal.setAttribute('width', this.width);
+				'y': y0,
-			this.fullMaskReveal.setAttribute('height', this.height);
+				'width': this.width,
+				'height': this.height,
+			};
 
-			this.lineMaskReveal.setAttribute('x', x0);
+			svg.setAttributes(this.fullMaskReveal, fullSize);
-			this.lineMaskReveal.setAttribute('y', y0);
+			svg.setAttributes(this.lineMaskReveal, fullSize);
-			this.lineMaskReveal.setAttribute('width', this.width);
-			this.lineMaskReveal.setAttribute('height', this.height);
 
 			this.base.setAttribute('viewBox', (
 				x0 + ' ' + y0 + ' ' +

scripts/sequence/Readme_spec.js

@@ -1,4 +1,4 @@
-defineDescribe('Readme', [
+define([
 	'./SequenceDiagram',
 	'image/ImageRegion',
 	'image/ImageSimilarity',
@@ -70,6 +70,8 @@ defineDescribe('Readme', [
 	return (fetch('README.md')
 		.then((response) => response.text())
 		.then(findSamples)
-		.then((samples) => samples.forEach(makeSampleTests))
+		.then((samples) => describe('Readme', () => {
+			samples.forEach(makeSampleTests);
+		}))
 	);
 });

scripts/sequence/Renderer.js

@@ -494,12 +494,13 @@ define([
 
 		updateBounds(stagesHeight) {
 			const cx = (this.minX + this.maxX) / 2;
-			const titleY = ((this.title.height > 0) ?
+			const titleSize = this.sizer.measure(this.title);
-				(-this.theme.titleMargin - this.title.height) : 0
+			const titleY = ((titleSize.height > 0) ?
+				(-this.theme.titleMargin - titleSize.height) : 0
 			);
 			this.title.set({x: cx, y: titleY});
 
-			const halfTitleWidth = this.title.width / 2;
+			const halfTitleWidth = titleSize.width / 2;
 			const margin = this.theme.outerMargin;
 			const x0 = Math.min(this.minX, cx - halfTitleWidth) - margin;
 			const x1 = Math.max(this.maxX, cx + halfTitleWidth) + margin;
@@ -509,15 +510,15 @@ define([
 			this.width = x1 - x0;
 			this.height = y1 - y0;
 
-			this.fullMaskReveal.setAttribute('x', x0);
+			const fullSize = {
-			this.fullMaskReveal.setAttribute('y', y0);
+				'x': x0,
-			this.fullMaskReveal.setAttribute('width', this.width);
+				'y': y0,
-			this.fullMaskReveal.setAttribute('height', this.height);
+				'width': this.width,
+				'height': this.height,
+			};
 
-			this.lineMaskReveal.setAttribute('x', x0);
+			svg.setAttributes(this.fullMaskReveal, fullSize);
-			this.lineMaskReveal.setAttribute('y', y0);
+			svg.setAttributes(this.lineMaskReveal, fullSize);
-			this.lineMaskReveal.setAttribute('width', this.width);
-			this.lineMaskReveal.setAttribute('height', this.height);
 
 			this.base.setAttribute('viewBox', (
 				x0 + ' ' + y0 + ' ' +

scripts/sequence/SequenceDiagram_spec.js

@@ -153,4 +153,35 @@ defineDescribe('SequenceDiagram', [
 		expect(content).toContain('<g class="region collapsed"');
 	});
 
+	it('measures OS fonts correctly on the first render', (done) => {
+		const code = 'title message';
+		const sd = new SequenceDiagram(code);
+		const widthImmediate = sd.getSize().width;
+		expect(widthImmediate).toBeGreaterThan(40);
+
+		sd.set(code);
+		expect(sd.getSize().width).toEqual(widthImmediate);
+
+		setTimeout(() => {
+			sd.set(code);
+			expect(sd.getSize().width).toEqual(widthImmediate);
+			done();
+		}, 500);
+	});
+
+	it('measures embedded fonts correctly on the first render', (done) => {
+		const code = 'theme sketch\ntitle message';
+		const sd = new SequenceDiagram(code);
+		const widthImmediate = sd.getSize().width;
+		expect(widthImmediate).toBeGreaterThan(40);
+
+		sd.set(code);
+		expect(sd.getSize().width).toEqual(widthImmediate);
+
+		setTimeout(() => {
+			sd.set(code);
+			expect(sd.getSize().width).toEqual(widthImmediate);
+			done();
+		}, 500);
+	});
 });

scripts/sequence/components/AgentCap.js

@@ -50,6 +50,7 @@ define([
 				boxLayer: clickable,
 				labelLayer: clickable,
 				SVGTextBlockClass: env.SVGTextBlockClass,
+				textSizer: env.textSizer,
 			});
 			clickable.insertBefore(svg.make('rect', {
 				'x': x - text.width / 2,

scripts/sequence/components/Block.js

@@ -56,6 +56,7 @@ define([
 				boxLayer: blockInfo.hold,
 				labelLayer: clickable,
 				SVGTextBlockClass: env.SVGTextBlockClass,
+				textSizer: env.textSizer,
 			});
 
 			const labelRender = SVGShapes.renderBoxedText(label, {
@@ -67,6 +68,7 @@ define([
 				boxLayer: env.lineMaskLayer,
 				labelLayer: clickable,
 				SVGTextBlockClass: env.SVGTextBlockClass,
+				textSizer: env.textSizer,
 			});
 
 			const labelHeight = Math.max(

scripts/sequence/components/Connect.js

@@ -227,6 +227,7 @@ define([
 				boxLayer: env.lineMaskLayer,
 				labelLayer: clickable,
 				SVGTextBlockClass: env.SVGTextBlockClass,
+				textSizer: env.textSizer,
 			});
 			const labelW = (label ? (
 				renderedText.width +
@@ -353,6 +354,7 @@ define([
 				boxLayer: env.lineMaskLayer,
 				labelLayer,
 				SVGTextBlockClass: env.SVGTextBlockClass,
+				textSizer: env.textSizer,
 			});
 		}
 

scripts/sequence/components/Divider.js

@@ -63,6 +63,7 @@ define([
 					boxLayer: env.fullMaskLayer,
 					labelLayer: clickable,
 					SVGTextBlockClass: env.SVGTextBlockClass,
+					textSizer: env.textSizer,
 				});
 				labelWidth = boxed.width;
 			}

scripts/sequence/components/Note.js

@@ -42,15 +42,16 @@ define(['./BaseComponent', 'svg/SVGUtilities'], (BaseComponent, svg) => {
 				formatted: label,
 				y,
 			});
+			const size = env.textSizer.measure(labelNode);
 
 			const fullW = (
-				labelNode.width +
+				size.width +
 				config.padding.left +
 				config.padding.right
 			);
 			const fullH = (
 				config.padding.top +
-				labelNode.height +
+				size.height +
 				config.padding.bottom
 			);
 			if(x0 === null && xMid !== null) {

scripts/stubs/SVGTextBlock.js

@@ -25,8 +25,6 @@ define(['svg/SVGUtilities'], (svg) => {
 				x: 0,
 				y: 0,
 			};
-			this.width = 0;
-			this.height = 0;
 			this.nodes = [];
 			this.set(initialState);
 		}
@@ -53,8 +51,6 @@ define(['svg/SVGUtilities'], (svg) => {
 
 		_reset() {
 			this._rebuildNodes(0);
-			this.width = 0;
-			this.height = 0;
 		}
 
 		_renderText() {
@@ -66,13 +62,10 @@ define(['svg/SVGUtilities'], (svg) => {
 			const formatted = this.state.formatted;
 			this._rebuildNodes(formatted.length);
 
-			let maxWidth = 0;
 			this.nodes.forEach(({text, element}, i) => {
 				const ln = formatted[i].reduce((v, pt) => v + pt.text, '');
 				text.nodeValue = ln;
-				maxWidth = Math.max(maxWidth, ln.length);
 			});
-			this.width = maxWidth;
 		}
 
 		_updateX() {
@@ -85,7 +78,6 @@ define(['svg/SVGUtilities'], (svg) => {
 			this.nodes.forEach(({element}, i) => {
 				element.setAttribute('y', this.state.y + i);
 			});
-			this.height = this.nodes.length;
 		}
 
 		firstLine() {
@@ -123,6 +115,11 @@ define(['svg/SVGUtilities'], (svg) => {
 
 	class SizeTester {
 		measure(attrs, formatted) {
+			if(attrs.state) {
+				formatted = attrs.state.formatted;
+				attrs = attrs.state.attrs;
+			}
+
 			if(!formatted || !formatted.length) {
 				return {width: 0, height: 0};
 			}

scripts/svg/SVGShapes.js

@@ -74,6 +74,7 @@ define([
 		labelLayer,
 		boxRenderer = null,
 		SVGTextBlockClass = SVGTextBlock,
+		textSizer,
 	}) {
 		if(!formatted || !formatted.length) {
 			return {width: 0, height: 0, label: null, box: null};
@@ -88,20 +89,21 @@ define([
 			y: y + padding.top,
 		});
 
-		const width = (label.width + padding.left + padding.right);
+		const size = textSizer.measure(label);
-		const height = (label.height + padding.top + padding.bottom);
+		const width = (size.width + padding.left + padding.right);
+		const height = (size.height + padding.top + padding.bottom);
 
 		let box = null;
 		if(boxRenderer) {
 			box = boxRenderer({
-				'x': anchorX - label.width * shift - padding.left,
+				'x': anchorX - size.width * shift - padding.left,
 				'y': y,
 				'width': width,
 				'height': height,
 			});
 		} else {
 			box = renderBox(boxAttrs, {
-				'x': anchorX - label.width * shift - padding.left,
+				'x': anchorX - size.width * shift - padding.left,
 				'y': y,
 				'width': width,
 				'height': height,

scripts/svg/SVGShapes_spec.js

@@ -54,8 +54,17 @@ defineDescribe('SVGShapes', ['./SVGShapes'], (SVGShapes) => {
 	});
 
 	describe('renderBoxedText', () => {
+		let o = null;
+		let sizer = null;
+
+		beforeEach(() => {
+			o = document.createElement('p');
+			sizer = {
+				measure: () => ({width: 64, height: 128}),
+			};
+		});
+
 		it('renders a label', () => {
-			const o = document.createElement('p');
 			const rendered = SVGShapes.renderBoxedText([[{text: 'foo'}]], {
 				x: 1,
 				y: 2,
@@ -64,6 +73,7 @@ defineDescribe('SVGShapes', ['./SVGShapes'], (SVGShapes) => {
 				labelAttrs: {'font-size': 10, 'line-height': 1.5, 'foo': 'bar'},
 				boxLayer: o,
 				labelLayer: o,
+				textSizer: sizer,
 			});
 			expect(rendered.label.state.formatted).toEqual([[{text: 'foo'}]]);
 			expect(rendered.label.state.x).toEqual(5);
@@ -72,7 +82,6 @@ defineDescribe('SVGShapes', ['./SVGShapes'], (SVGShapes) => {
 		});
 
 		it('positions a box beneath the rendered label', () => {
-			const o = document.createElement('p');
 			const rendered = SVGShapes.renderBoxedText([[{text: 'foo'}]], {
 				x: 1,
 				y: 2,
@@ -81,16 +90,19 @@ defineDescribe('SVGShapes', ['./SVGShapes'], (SVGShapes) => {
 				labelAttrs: {'font-size': 10, 'line-height': 1.5},
 				boxLayer: o,
 				labelLayer: o,
+				textSizer: sizer,
 			});
 			expect(rendered.box.getAttribute('x')).toEqual('1');
 			expect(rendered.box.getAttribute('y')).toEqual('2');
-			expect(rendered.box.getAttribute('height')).toEqual('55');
+			expect(rendered.box.getAttribute('width'))
+				.toEqual(String(4 + 16 + 64));
+			expect(rendered.box.getAttribute('height'))
+				.toEqual(String(8 + 32 + 128));
 			expect(rendered.box.getAttribute('foo')).toEqual('bar');
 			expect(rendered.box.parentNode).toEqual(o);
 		});
 
 		it('returns the size of the rendered box', () => {
-			const o = document.createElement('p');
 			const rendered = SVGShapes.renderBoxedText([[{text: 'foo'}]], {
 				x: 1,
 				y: 2,
@@ -99,9 +111,10 @@ defineDescribe('SVGShapes', ['./SVGShapes'], (SVGShapes) => {
 				labelAttrs: {'font-size': 10, 'line-height': 1.5},
 				boxLayer: o,
 				labelLayer: o,
+				textSizer: sizer,
 			});
-			expect(rendered.width).toBeGreaterThan(20 - 1);
+			expect(rendered.width).toEqual(4 + 16 + 64);
-			expect(rendered.height).toEqual(55);
+			expect(rendered.height).toEqual(8 + 32 + 128);
 		});
 	});
 });

scripts/svg/SVGTextBlock.js

@@ -38,6 +38,27 @@ define(['./SVGUtilities'], (svg) => {
 		});
 	}
 
+	function measureLine(tester, line) {
+		if(!line.length) {
+			return 0;
+		}
+
+		const labelKey = JSON.stringify(line);
+		const knownWidth = tester.widths.get(labelKey);
+		if(knownWidth !== undefined) {
+			return knownWidth;
+		}
+
+		// getComputedTextLength forces a reflow, so only call it if nothing
+		// else can tell us the length
+
+		svg.empty(tester.node);
+		populateSvgTextLine(tester.node, line);
+		const width = tester.node.getComputedTextLength();
+		tester.widths.set(labelKey, width);
+		return width;
+	}
+
 	const EMPTY = [];
 
 	class SVGTextBlock {
@@ -49,8 +70,6 @@ define(['./SVGUtilities'], (svg) => {
 				x: 0,
 				y: 0,
 			};
-			this.width = 0;
-			this.height = 0;
 			this.lines = [];
 			this.set(initialState);
 		}
@@ -76,8 +95,6 @@ define(['./SVGUtilities'], (svg) => {
 
 		_reset() {
 			this._rebuildLines(0);
-			this.width = 0;
-			this.height = 0;
 		}
 
 		_renderText() {
@@ -93,7 +110,6 @@ define(['./SVGUtilities'], (svg) => {
 
 			this._rebuildLines(formatted.length);
 
-			let maxWidth = 0;
 			this.lines.forEach((ln, i) => {
 				const id = JSON.stringify(formatted[i]);
 				if(id !== ln.latest) {
@@ -101,9 +117,7 @@ define(['./SVGUtilities'], (svg) => {
 					populateSvgTextLine(ln.node, formatted[i]);
 					ln.latest = id;
 				}
-				maxWidth = Math.max(maxWidth, ln.node.getComputedTextLength());
 			});
-			this.width = maxWidth;
 		}
 
 		_updateX() {
@@ -117,7 +131,6 @@ define(['./SVGUtilities'], (svg) => {
 			this.lines.forEach(({node}, i) => {
 				node.setAttribute('y', this.state.y + i * lineHeight + size);
 			});
-			this.height = lineHeight * this.lines.length;
 		}
 
 		firstLine() {
@@ -164,47 +177,62 @@ define(['./SVGUtilities'], (svg) => {
 			this.cache = new Map();
 		}
 
-		measure(attrs, formatted) {
+		_measureHeight({attrs, formatted}) {
-			if(!formatted || !formatted.length) {
+			return formatted.length * fontDetails(attrs).lineHeight;
-				return {width: 0, height: 0};
-			}
-			if(!Array.isArray(formatted)) {
-				throw new Error('Invalid formatted text: ' + formatted);
 		}
 
-			let tester = this.cache.get(attrs);
+		_measureWidth({attrs, formatted}) {
+			if(!formatted.length) {
+				return 0;
+			}
+
+			const attrKey = JSON.stringify(attrs);
+			let tester = this.cache.get(attrKey);
 			if(!tester) {
-				tester = svg.make('text', attrs);
+				const node = svg.make('text', attrs);
-				this.testers.appendChild(tester);
+				this.testers.appendChild(node);
-				this.cache.set(attrs, tester);
+				tester = {
+					node,
+					widths: new Map(),
+				};
+				this.cache.set(attrKey, tester);
 			}
 
 			if(!this.testers.parentNode) {
 				this.container.appendChild(this.testers);
 			}
 
-			let width = 0;
+			return (formatted
-			formatted.forEach((line) => {
+				.map((line) => measureLine(tester, line))
-				svg.empty(tester);
+				.reduce((a, b) => Math.max(a, b), 0)
-				populateSvgTextLine(tester, line);
+			);
-				width = Math.max(width, tester.getComputedTextLength());
+		}
-			});
 
+		_getMeasurementOpts(attrs, formatted) {
+			if(!formatted) {
+				if(typeof attrs === 'object' && attrs.state) {
+					formatted = attrs.state.formatted || [];
+					attrs = attrs.state.attrs;
+				} else {
+					formatted = [];
+				}
+			} else if(!Array.isArray(formatted)) {
+				throw new Error('Invalid formatted text: ' + formatted);
+			}
+			return {attrs, formatted};
+		}
+
+		measure(attrs, formatted) {
+			const opts = this._getMeasurementOpts(attrs, formatted);
 			return {
-				width,
+				width: this._measureWidth(opts),
-				height: formatted.length * fontDetails(attrs).lineHeight,
+				height: this._measureHeight(opts),
 			};
 		}
 
 		measureHeight(attrs, formatted) {
-			if(!formatted) {
+			const opts = this._getMeasurementOpts(attrs, formatted);
-				return 0;
+			return this._measureHeight(opts);
-			}
-			if(!Array.isArray(formatted)) {
-				throw new Error('Invalid formatted text: ' + formatted);
-			}
-
-			return formatted.length * fontDetails(attrs).lineHeight;
 		}
 
 		resetCache() {

scripts/svg/SVGTextBlock_spec.js

@@ -68,12 +68,6 @@ defineDescribe('SVGTextBlock', [
 			expect(hold.children[1].innerHTML).toEqual('bar');
 		});
 
-		it('populates width and height with the size of the text', () => {
-			block.set({formatted: [[{text: 'foo'}], [{text: 'bar'}]]});
-			expect(block.width).toBeGreaterThan(0);
-			expect(block.height).toEqual(30);
-		});
-
 		it('re-uses text nodes when possible, adding more if needed', () => {
 			block.set({formatted: [[{text: 'foo'}], [{text: 'bar'}]]});
 			const line0 = hold.children[0];
@@ -129,8 +123,7 @@ defineDescribe('SVGTextBlock', [
 			block.set({formatted: []});
 			expect(hold.children.length).toEqual(0);
 			expect(block.state.formatted).toEqual([]);
-			expect(block.width).toEqual(0);
+			expect(block.lines.length).toEqual(0);
-			expect(block.height).toEqual(0);
 		});
 	});
 
@@ -148,6 +141,13 @@ defineDescribe('SVGTextBlock', [
 				expect(size.height).toEqual(15);
 			});
 
+			it('calculates the size of text blocks', () => {
+				block.set({formatted: [[{text: 'foo'}]]});
+				const size = tester.measure(block);
+				expect(size.width).toBeGreaterThan(0);
+				expect(size.height).toEqual(15);
+			});
+
 			it('measures multiline text', () => {
 				const size = tester.measure(attrs, [
 					[{text: 'foo'}],

scripts/svg/SVGUtilities.js

@@ -7,13 +7,17 @@ define(() => {
 		return document.createTextNode(text);
 	}
 
-	function make(type, attrs = {}, children = []) {
+	function setAttributes(target, attrs) {
-		const o = document.createElementNS(NS, type);
 		for(const k in attrs) {
 			if(attrs.hasOwnProperty(k)) {
-				o.setAttribute(k, attrs[k]);
+				target.setAttribute(k, attrs[k]);
 			}
 		}
+	}
+
+	function make(type, attrs = {}, children = []) {
+		const o = document.createElementNS(NS, type);
+		setAttributes(o, attrs);
 		for(const c of children) {
 			o.appendChild(c);
 		}
@@ -37,6 +41,7 @@ define(() => {
 		makeText,
 		make,
 		makeContainer,
+		setAttributes,
 		empty,
 	};
 });