pdf.js/src/display/font_loader.js

/* Copyright 2012 Mozilla Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import {
  assert,
  bytesToString,
  FeatureTest,
  isNodeJS,
  shadow,
  string32,
  unreachable,
  warn,
} from "../shared/util.js";

class FontLoader {
  #systemFonts = new Set();

  constructor({
    ownerDocument = globalThis.document,
    styleElement = null, // For testing only.
  }) {
    this._document = ownerDocument;

    this.nativeFontFaces = new Set();
    this.styleElement =
      typeof PDFJSDev === "undefined" || PDFJSDev.test("TESTING")
        ? styleElement
        : null;

    if (typeof PDFJSDev === "undefined" || !PDFJSDev.test("MOZCENTRAL")) {
      this.loadingRequests = [];
      this.loadTestFontId = 0;
    }
  }

  addNativeFontFace(nativeFontFace) {
    this.nativeFontFaces.add(nativeFontFace);
    this._document.fonts.add(nativeFontFace);
  }

  removeNativeFontFace(nativeFontFace) {
    this.nativeFontFaces.delete(nativeFontFace);
    this._document.fonts.delete(nativeFontFace);
  }

  insertRule(rule) {
    if (!this.styleElement) {
      this.styleElement = this._document.createElement("style");
      this._document.documentElement
        .getElementsByTagName("head")[0]
        .append(this.styleElement);
    }
    const styleSheet = this.styleElement.sheet;
    styleSheet.insertRule(rule, styleSheet.cssRules.length);
  }

  clear() {
    for (const nativeFontFace of this.nativeFontFaces) {
      this._document.fonts.delete(nativeFontFace);
    }
    this.nativeFontFaces.clear();
    this.#systemFonts.clear();

    if (this.styleElement) {
      // Note: ChildNode.remove doesn't throw if the parentNode is undefined.
      this.styleElement.remove();
      this.styleElement = null;
    }
  }

  async loadSystemFont(info) {
    if (!info || this.#systemFonts.has(info.loadedName)) {
      return;
    }
    assert(
      !this.disableFontFace,
      "loadSystemFont shouldn't be called when `disableFontFace` is set."
    );

    if (this.isFontLoadingAPISupported) {
      const { loadedName, src, style } = info;
      const fontFace = new FontFace(loadedName, src, style);
      this.addNativeFontFace(fontFace);
      try {
        await fontFace.load();
        this.#systemFonts.add(loadedName);
      } catch {
        warn(
          `Cannot load system font: ${info.baseFontName}, installing it could help to improve PDF rendering.`
        );

        this.removeNativeFontFace(fontFace);
      }
      return;
    }

    unreachable(
      "Not implemented: loadSystemFont without the Font Loading API."
    );
  }

  async bind(font) {
    // Add the font to the DOM only once; skip if the font is already loaded.
    if (font.attached || (font.missingFile && !font.systemFontInfo)) {
      return;
    }
    font.attached = true;

    if (font.systemFontInfo) {
      await this.loadSystemFont(font.systemFontInfo);
      return;
    }

    if (this.isFontLoadingAPISupported) {
      const nativeFontFace = font.createNativeFontFace();
      if (nativeFontFace) {
        this.addNativeFontFace(nativeFontFace);
        try {
          await nativeFontFace.loaded;
        } catch (ex) {
          warn(`Failed to load font '${nativeFontFace.family}': '${ex}'.`);

          // When font loading failed, fall back to the built-in font renderer.
          font.disableFontFace = true;
          throw ex;
        }
      }
      return; // The font was, asynchronously, loaded.
    }

    // !this.isFontLoadingAPISupported
    const rule = font.createFontFaceRule();
    if (rule) {
      this.insertRule(rule);

      if (this.isSyncFontLoadingSupported) {
        return; // The font was, synchronously, loaded.
      }
      if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("MOZCENTRAL")) {
        throw new Error("Not implemented: async font loading");
      }
      await new Promise(resolve => {
        const request = this._queueLoadingCallback(resolve);
        this._prepareFontLoadEvent(font, request);
      });
      // The font was, asynchronously, loaded.
    }
  }

  get isFontLoadingAPISupported() {
    const hasFonts = !!this._document?.fonts;
    if (typeof PDFJSDev === "undefined" || PDFJSDev.test("TESTING")) {
      return shadow(
        this,
        "isFontLoadingAPISupported",
        hasFonts && !this.styleElement
      );
    }
    return shadow(this, "isFontLoadingAPISupported", hasFonts);
  }

  get isSyncFontLoadingSupported() {
    if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("MOZCENTRAL")) {
      return shadow(this, "isSyncFontLoadingSupported", true);
    }

    let supported = false;
    if (typeof PDFJSDev === "undefined" || !PDFJSDev.test("CHROME")) {
      if (isNodeJS) {
        // Node.js - we can pretend that sync font loading is supported.
        supported = true;
      } else if (
        typeof navigator !== "undefined" &&
        // User agent string sniffing is bad, but there is no reliable way to
        // tell if the font is fully loaded and ready to be used with canvas.
        /Mozilla\/5.0.*?rv:\d+.*? Gecko/.test(navigator.userAgent)
      ) {
        // Firefox, from version 14, supports synchronous font loading.
        supported = true;
      }
    }
    return shadow(this, "isSyncFontLoadingSupported", supported);
  }

  _queueLoadingCallback(callback) {
    if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("MOZCENTRAL")) {
      throw new Error("Not implemented: _queueLoadingCallback");
    }

    function completeRequest() {
      assert(!request.done, "completeRequest() cannot be called twice.");
      request.done = true;

      // Sending all completed requests in order of how they were queued.
      while (loadingRequests.length > 0 && loadingRequests[0].done) {
        const otherRequest = loadingRequests.shift();
        setTimeout(otherRequest.callback, 0);
      }
    }

    const { loadingRequests } = this;
    const request = {
      done: false,
      complete: completeRequest,
      callback,
    };
    loadingRequests.push(request);
    return request;
  }

  get _loadTestFont() {
    if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("MOZCENTRAL")) {
      throw new Error("Not implemented: _loadTestFont");
    }

    // This is a CFF font with 1 glyph for '.' that fills its entire width
    // and height.
    const testFont = atob(
      "T1RUTwALAIAAAwAwQ0ZGIDHtZg4AAAOYAAAAgUZGVE1lkzZwAAAEHAAAABxHREVGABQA" +
        "FQAABDgAAAAeT1MvMlYNYwkAAAEgAAAAYGNtYXABDQLUAAACNAAAAUJoZWFk/xVFDQAA" +
        "ALwAAAA2aGhlYQdkA+oAAAD0AAAAJGhtdHgD6AAAAAAEWAAAAAZtYXhwAAJQAAAAARgA" +
        "AAAGbmFtZVjmdH4AAAGAAAAAsXBvc3T/hgAzAAADeAAAACAAAQAAAAEAALZRFsRfDzz1" +
        "AAsD6AAAAADOBOTLAAAAAM4KHDwAAAAAA+gDIQAAAAgAAgAAAAAAAAABAAADIQAAAFoD" +
        "6AAAAAAD6AABAAAAAAAAAAAAAAAAAAAAAQAAUAAAAgAAAAQD6AH0AAUAAAKKArwAAACM" +
        "AooCvAAAAeAAMQECAAACAAYJAAAAAAAAAAAAAQAAAAAAAAAAAAAAAFBmRWQAwAAuAC4D" +
        "IP84AFoDIQAAAAAAAQAAAAAAAAAAACAAIAABAAAADgCuAAEAAAAAAAAAAQAAAAEAAAAA" +
        "AAEAAQAAAAEAAAAAAAIAAQAAAAEAAAAAAAMAAQAAAAEAAAAAAAQAAQAAAAEAAAAAAAUA" +
        "AQAAAAEAAAAAAAYAAQAAAAMAAQQJAAAAAgABAAMAAQQJAAEAAgABAAMAAQQJAAIAAgAB" +
        "AAMAAQQJAAMAAgABAAMAAQQJAAQAAgABAAMAAQQJAAUAAgABAAMAAQQJAAYAAgABWABY" +
        "AAAAAAAAAwAAAAMAAAAcAAEAAAAAADwAAwABAAAAHAAEACAAAAAEAAQAAQAAAC7//wAA" +
        "AC7////TAAEAAAAAAAABBgAAAQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" +
        "AAAAAAAAAAAAAAAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" +
        "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" +
        "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" +
        "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" +
        "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAMAAAAAAAD/gwAyAAAAAQAAAAAAAAAAAAAAAAAA" +
        "AAABAAQEAAEBAQJYAAEBASH4DwD4GwHEAvgcA/gXBIwMAYuL+nz5tQXkD5j3CBLnEQAC" +
        "AQEBIVhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYAAABAQAADwACAQEEE/t3" +
        "Dov6fAH6fAT+fPp8+nwHDosMCvm1Cvm1DAz6fBQAAAAAAAABAAAAAMmJbzEAAAAAzgTj" +
        "FQAAAADOBOQpAAEAAAAAAAAADAAUAAQAAAABAAAAAgABAAAAAAAAAAAD6AAAAAAAAA=="
    );
    return shadow(this, "_loadTestFont", testFont);
  }

  _prepareFontLoadEvent(font, request) {
    if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("MOZCENTRAL")) {
      throw new Error("Not implemented: _prepareFontLoadEvent");
    }

    /** Hack begin */
    // There's currently no event when a font has finished downloading so the
    // following code is a dirty hack to 'guess' when a font is ready.
    // It's assumed fonts are loaded in order, so add a known test font after
    // the desired fonts and then test for the loading of that test font.

    function int32(data, offset) {
      return (
        (data.charCodeAt(offset) << 24) |
        (data.charCodeAt(offset + 1) << 16) |
        (data.charCodeAt(offset + 2) << 8) |
        (data.charCodeAt(offset + 3) & 0xff)
      );
    }
    function spliceString(s, offset, remove, insert) {
      const chunk1 = s.substring(0, offset);
      const chunk2 = s.substring(offset + remove);
      return chunk1 + insert + chunk2;
    }
    let i, ii;

    // The temporary canvas is used to determine if fonts are loaded.
    const canvas = this._document.createElement("canvas");
    canvas.width = 1;
    canvas.height = 1;
    const ctx = canvas.getContext("2d");

    let called = 0;
    function isFontReady(name, callback) {
      // With setTimeout clamping this gives the font ~100ms to load.
      if (++called > 30) {
        warn("Load test font never loaded.");
        callback();
        return;
      }
      ctx.font = "30px " + name;
      ctx.fillText(".", 0, 20);
      const imageData = ctx.getImageData(0, 0, 1, 1);
      if (imageData.data[3] > 0) {
        callback();
        return;
      }
      setTimeout(isFontReady.bind(null, name, callback));
    }

    const loadTestFontId = `lt${Date.now()}${this.loadTestFontId++}`;
    // Chromium seems to cache fonts based on a hash of the actual font data,
    // so the font must be modified for each load test else it will appear to
    // be loaded already.
    // TODO: This could maybe be made faster by avoiding the btoa of the full
    // font by splitting it in chunks before hand and padding the font id.
    let data = this._loadTestFont;
    const COMMENT_OFFSET = 976; // has to be on 4 byte boundary (for checksum)
    data = spliceString(
      data,
      COMMENT_OFFSET,
      loadTestFontId.length,
      loadTestFontId
    );
    // CFF checksum is important for IE, adjusting it
    const CFF_CHECKSUM_OFFSET = 16;
    const XXXX_VALUE = 0x58585858; // the "comment" filled with 'X'
    let checksum = int32(data, CFF_CHECKSUM_OFFSET);
    for (i = 0, ii = loadTestFontId.length - 3; i < ii; i += 4) {
      checksum = (checksum - XXXX_VALUE + int32(loadTestFontId, i)) | 0;
    }
    if (i < loadTestFontId.length) {
      // align to 4 bytes boundary
      checksum = (checksum - XXXX_VALUE + int32(loadTestFontId + "XXX", i)) | 0;
    }
    data = spliceString(data, CFF_CHECKSUM_OFFSET, 4, string32(checksum));

    const url = `url(data:font/opentype;base64,${btoa(data)});`;
    const rule = `@font-face {font-family:"${loadTestFontId}";src:${url}}`;
    this.insertRule(rule);

    const div = this._document.createElement("div");
    div.style.visibility = "hidden";
    div.style.width = div.style.height = "10px";
    div.style.position = "absolute";
    div.style.top = div.style.left = "0px";

    for (const name of [font.loadedName, loadTestFontId]) {
      const span = this._document.createElement("span");
      span.textContent = "Hi";
      span.style.fontFamily = name;
      div.append(span);
    }
    this._document.body.append(div);

    isFontReady(loadTestFontId, () => {
      div.remove();
      request.complete();
    });
    /** Hack end */
  }
}

class FontFaceObject {
  constructor(
    translatedData,
    {
      isEvalSupported = true,
      disableFontFace = false,
      ignoreErrors = false,
      inspectFont = null,
    }
  ) {
    this.compiledGlyphs = Object.create(null);
    // importing translated data
    for (const i in translatedData) {
      this[i] = translatedData[i];
    }
    this.isEvalSupported = isEvalSupported !== false;
    this.disableFontFace = disableFontFace === true;
    this.ignoreErrors = ignoreErrors === true;
    this._inspectFont = inspectFont;
  }

  createNativeFontFace() {
    if (!this.data || this.disableFontFace) {
      return null;
    }
    let nativeFontFace;
    if (!this.cssFontInfo) {
      nativeFontFace = new FontFace(this.loadedName, this.data, {});
    } else {
      const css = {
        weight: this.cssFontInfo.fontWeight,
      };
      if (this.cssFontInfo.italicAngle) {
        css.style = `oblique ${this.cssFontInfo.italicAngle}deg`;
      }
      nativeFontFace = new FontFace(
        this.cssFontInfo.fontFamily,
        this.data,
        css
      );
    }

    this._inspectFont?.(this);
    return nativeFontFace;
  }

  createFontFaceRule() {
    if (!this.data || this.disableFontFace) {
      return null;
    }
    const data = bytesToString(this.data);
    // Add the @font-face rule to the document.
    const url = `url(data:${this.mimetype};base64,${btoa(data)});`;
    let rule;
    if (!this.cssFontInfo) {
      rule = `@font-face {font-family:"${this.loadedName}";src:${url}}`;
    } else {
      let css = `font-weight: ${this.cssFontInfo.fontWeight};`;
      if (this.cssFontInfo.italicAngle) {
        css += `font-style: oblique ${this.cssFontInfo.italicAngle}deg;`;
      }
      rule = `@font-face {font-family:"${this.cssFontInfo.fontFamily}";${css}src:${url}}`;
    }

    this._inspectFont?.(this, url);
    return rule;
  }

  getPathGenerator(objs, character) {
    if (this.compiledGlyphs[character] !== undefined) {
      return this.compiledGlyphs[character];
    }

    let cmds;
    try {
      cmds = objs.get(this.loadedName + "_path_" + character);
    } catch (ex) {
      if (!this.ignoreErrors) {
        throw ex;
      }
      warn(`getPathGenerator - ignoring character: "${ex}".`);

      return (this.compiledGlyphs[character] = function (c, size) {
        // No-op function, to allow rendering to continue.
      });
    }

    // If we can, compile cmds into JS for MAXIMUM SPEED...
    if (this.isEvalSupported && FeatureTest.isEvalSupported) {
      const jsBuf = [];
      for (const current of cmds) {
        const args = current.args !== undefined ? current.args.join(",") : "";
        jsBuf.push("c.", current.cmd, "(", args, ");\n");
      }
      // eslint-disable-next-line no-new-func
      return (this.compiledGlyphs[character] = new Function(
        "c",
        "size",
        jsBuf.join("")
      ));
    }
    // ... but fall back on using Function.prototype.apply() if we're
    // blocked from using eval() for whatever reason (like CSP policies).
    return (this.compiledGlyphs[character] = function (c, size) {
      for (const current of cmds) {
        if (current.cmd === "scale") {
          current.args = [size, -size];
        }
        // eslint-disable-next-line prefer-spread
        c[current.cmd].apply(c, current.args);
      }
    });
  }
}

export { FontFaceObject, FontLoader };