73 lines
2.1 KiB
TypeScript
73 lines
2.1 KiB
TypeScript
import {SMALL_IMAGE} from '../core/util';
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export interface FontMetric {
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baseline: number;
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middle: number;
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}
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const SAMPLE_TEXT = 'Hidden Text';
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export class FontMetrics {
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private readonly _data: {[key: string]: FontMetric};
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private readonly _document: Document;
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constructor(document: Document) {
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this._data = {};
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this._document = document;
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}
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private parseMetrics(fontFamily: string, fontSize: string): FontMetric {
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const container = this._document.createElement('div');
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const img = this._document.createElement('img');
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const span = this._document.createElement('span');
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const body = this._document.body as HTMLBodyElement;
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container.style.visibility = 'hidden';
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container.style.fontFamily = fontFamily;
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container.style.fontSize = fontSize;
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container.style.margin = '0';
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container.style.padding = '0';
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container.style.whiteSpace = 'nowrap';
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body.appendChild(container);
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img.src = SMALL_IMAGE;
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img.width = 1;
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img.height = 1;
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img.style.margin = '0';
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img.style.padding = '0';
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img.style.verticalAlign = 'baseline';
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span.style.fontFamily = fontFamily;
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span.style.fontSize = fontSize;
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span.style.margin = '0';
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span.style.padding = '0';
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span.appendChild(this._document.createTextNode(SAMPLE_TEXT));
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container.appendChild(span);
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container.appendChild(img);
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const baseline = img.offsetTop - span.offsetTop + 2;
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container.removeChild(span);
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container.appendChild(this._document.createTextNode(SAMPLE_TEXT));
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container.style.lineHeight = 'normal';
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img.style.verticalAlign = 'super';
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const middle = img.offsetTop - container.offsetTop + 2;
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body.removeChild(container);
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return {baseline, middle};
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}
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getMetrics(fontFamily: string, fontSize: string): FontMetric {
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const key = `${fontFamily} ${fontSize}`;
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if (typeof this._data[key] === 'undefined') {
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this._data[key] = this.parseMetrics(fontFamily, fontSize);
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}
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return this._data[key];
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}
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}
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