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,
  IsEvalSupportedCached,
  shadow,
  string32,
  unreachable,
  UNSUPPORTED_FEATURES,
  warn,
} from "../shared/util.js";

class BaseFontLoader {
  constructor({ docId, onUnsupportedFeature }) {
    if (this.constructor === BaseFontLoader) {
      unreachable("Cannot initialize BaseFontLoader.");
    }
    this.docId = docId;
    this._onUnsupportedFeature = onUnsupportedFeature;

    this.nativeFontFaces = [];
    this.styleElement = null;
  }

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

  insertRule(rule) {
    let styleElement = this.styleElement;
    if (!styleElement) {
      styleElement = this.styleElement = document.createElement("style");
      styleElement.id = `PDFJS_FONT_STYLE_TAG_${this.docId}`;
      document.documentElement
        .getElementsByTagName("head")[0]
        .appendChild(styleElement);
    }

    const styleSheet = styleElement.sheet;
    styleSheet.insertRule(rule, styleSheet.cssRules.length);
  }

  clear() {
    this.nativeFontFaces.forEach(function (nativeFontFace) {
      document.fonts.delete(nativeFontFace);
    });
    this.nativeFontFaces.length = 0;

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

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

    if (this.isFontLoadingAPISupported) {
      const nativeFontFace = font.createNativeFontFace();
      if (nativeFontFace) {
        this.addNativeFontFace(nativeFontFace);
        try {
          await nativeFontFace.loaded;
        } catch (ex) {
          this._onUnsupportedFeature({
            featureId: UNSUPPORTED_FEATURES.errorFontLoadNative,
          });
          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.
      }
      await new Promise(resolve => {
        const request = this._queueLoadingCallback(resolve);
        this._prepareFontLoadEvent([rule], [font], request);
      });
      // The font was, asynchronously, loaded.
    }
  }

  _queueLoadingCallback(callback) {
    unreachable("Abstract method `_queueLoadingCallback`.");
  }

  get isFontLoadingAPISupported() {
    const supported = typeof document !== "undefined" && !!document.fonts;
    return shadow(this, "isFontLoadingAPISupported", supported);
  }

  // eslint-disable-next-line getter-return
  get isSyncFontLoadingSupported() {
    unreachable("Abstract method `isSyncFontLoadingSupported`.");
  }

  // eslint-disable-next-line getter-return
  get _loadTestFont() {
    unreachable("Abstract method `_loadTestFont`.");
  }

  _prepareFontLoadEvent(rules, fontsToLoad, request) {
    unreachable("Abstract method `_prepareFontLoadEvent`.");
  }
}

let FontLoader;
if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("MOZCENTRAL")) {
  FontLoader = class MozcentralFontLoader extends BaseFontLoader {
    get isSyncFontLoadingSupported() {
      return shadow(this, "isSyncFontLoadingSupported", true);
    }
  };
} else {
  // PDFJSDev.test('CHROME || GENERIC')

  FontLoader = class GenericFontLoader extends BaseFontLoader {
    constructor(docId) {
      super(docId);
      this.loadingContext = {
        requests: [],
        nextRequestId: 0,
      };
      this.loadTestFontId = 0;
    }

    get isSyncFontLoadingSupported() {
      let supported = false;
      if (typeof PDFJSDev === "undefined" || !PDFJSDev.test("CHROME")) {
        if (typeof navigator === "undefined") {
          // Node.js - we can pretend that sync font loading is supported.
          supported = true;
        } else {
          // 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.
          const m = /Mozilla\/5.0.*?rv:(\d+).*? Gecko/.exec(
            navigator.userAgent
          );
          if (m && m[1] >= 14) {
            supported = true;
          }
          // TODO - other browsers...
        }
      }
      return shadow(this, "isSyncFontLoadingSupported", supported);
    }

    _queueLoadingCallback(callback) {
      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 (context.requests.length > 0 && context.requests[0].done) {
          const otherRequest = context.requests.shift();
          setTimeout(otherRequest.callback, 0);
        }
      }

      const context = this.loadingContext;
      const request = {
        id: `pdfjs-font-loading-${context.nextRequestId++}`,
        done: false,
        complete: completeRequest,
        callback,
      };
      context.requests.push(request);
      return request;
    }

    get _loadTestFont() {
      const getLoadTestFont = function () {
        // This is a CFF font with 1 glyph for '.' that fills its entire width
        // and height.
        return 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", getLoadTestFont());
    }

    _prepareFontLoadEvent(rules, fonts, request) {
      /** 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 = document.createElement("canvas");
      canvas.width = 1;
      canvas.height = 1;
      const ctx = canvas.getContext("2d");

      let called = 0;
      function isFontReady(name, callback) {
        called++;
        // 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 names = [];
      for (i = 0, ii = fonts.length; i < ii; i++) {
        names.push(fonts[i].loadedName);
      }
      names.push(loadTestFontId);

      const div = 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 (i = 0, ii = names.length; i < ii; ++i) {
        const span = document.createElement("span");
        span.textContent = "Hi";
        span.style.fontFamily = names[i];
        div.appendChild(span);
      }
      document.body.appendChild(div);

      isFontReady(loadTestFontId, function () {
        document.body.removeChild(div);
        request.complete();
      });
      /** Hack end */
    }
  };
} // End of PDFJSDev.test('CHROME || GENERIC')

class FontFaceObject {
  constructor(
    translatedData,
    {
      isEvalSupported = true,
      disableFontFace = false,
      ignoreErrors = false,
      onUnsupportedFeature = null,
      fontRegistry = 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._onUnsupportedFeature = onUnsupportedFeature;
    this.fontRegistry = fontRegistry;
  }

  createNativeFontFace() {
    if (!this.data || this.disableFontFace) {
      return null;
    }
    const nativeFontFace = new FontFace(this.loadedName, this.data, {});

    if (this.fontRegistry) {
      this.fontRegistry.registerFont(this);
    }
    return nativeFontFace;
  }

  createFontFaceRule() {
    if (!this.data || this.disableFontFace) {
      return null;
    }
    const data = bytesToString(new Uint8Array(this.data));
    // Add the @font-face rule to the document.
    const url = `url(data:${this.mimetype};base64,${btoa(data)});`;
    const rule = `@font-face {font-family:"${this.loadedName}";src:${url}}`;

    if (this.fontRegistry) {
      this.fontRegistry.registerFont(this, url);
    }
    return rule;
  }

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

    let cmds, current;
    try {
      cmds = objs.get(this.loadedName + "_path_" + character);
    } catch (ex) {
      if (!this.ignoreErrors) {
        throw ex;
      }
      if (this._onUnsupportedFeature) {
        this._onUnsupportedFeature({
          featureId: UNSUPPORTED_FEATURES.errorFontGetPath,
        });
      }
      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 && IsEvalSupportedCached.value) {
      let args,
        js = "";
      for (let i = 0, ii = cmds.length; i < ii; i++) {
        current = cmds[i];

        if (current.args !== undefined) {
          args = current.args.join(",");
        } else {
          args = "";
        }
        js += "c." + current.cmd + "(" + args + ");\n";
      }
      // eslint-disable-next-line no-new-func
      return (this.compiledGlyphs[character] = new Function("c", "size", js));
    }
    // ... 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 (let i = 0, ii = cmds.length; i < ii; i++) {
        current = cmds[i];

        if (current.cmd === "scale") {
          current.args = [size, -size];
        }
        c[current.cmd].apply(c, current.args);
      }
    });
  }
}

export { FontFaceObject, FontLoader };