pdf.js/src/core/default_appearance.js

/* Copyright 2020 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 { isName, Name } from "./primitives.js";
import { OPS, warn } from "../shared/util.js";
import { ColorSpace } from "./colorspace.js";
import { escapePDFName } from "./core_utils.js";
import { EvaluatorPreprocessor } from "./evaluator.js";
import { StringStream } from "./stream.js";

class DefaultAppearanceEvaluator extends EvaluatorPreprocessor {
  constructor(str) {
    super(new StringStream(str));
  }

  parse() {
    const operation = {
      fn: 0,
      args: [],
    };
    const result = {
      fontSize: 0,
      fontName: Name.get(""),
      fontColor: new Uint8ClampedArray([0, 0, 0]) /* black */,
    };

    try {
      while (true) {
        operation.args.length = 0; // Ensure that `args` it's always reset.

        if (!this.read(operation)) {
          break;
        }
        if (this.savedStatesDepth !== 0) {
          continue; // Don't get info in save/restore sections.
        }
        const { fn, args } = operation;

        switch (fn | 0) {
          case OPS.setFont:
            const [fontName, fontSize] = args;
            if (isName(fontName)) {
              result.fontName = fontName;
            }
            if (typeof fontSize === "number" && fontSize > 0) {
              result.fontSize = fontSize;
            }
            break;
          case OPS.setFillRGBColor:
            ColorSpace.singletons.rgb.getRgbItem(args, 0, result.fontColor, 0);
            break;
          case OPS.setFillGray:
            ColorSpace.singletons.gray.getRgbItem(args, 0, result.fontColor, 0);
            break;
          case OPS.setFillColorSpace:
            ColorSpace.singletons.cmyk.getRgbItem(args, 0, result.fontColor, 0);
            break;
        }
      }
    } catch (reason) {
      warn(`parseDefaultAppearance - ignoring errors: "${reason}".`);
    }

    return result;
  }
}

// Parse DA to extract font and color information.
function parseDefaultAppearance(str) {
  return new DefaultAppearanceEvaluator(str).parse();
}

// Create default appearance string from some information.
function createDefaultAppearance({ fontSize, fontName, fontColor }) {
  let colorCmd;
  if (fontColor.every(c => c === 0)) {
    colorCmd = "0 g";
  } else {
    colorCmd =
      Array.from(fontColor)
        .map(c => (c / 255).toFixed(2))
        .join(" ") + " rg";
  }
  return `/${escapePDFName(fontName.name)} ${fontSize} Tf ${colorCmd}`;
}

export { createDefaultAppearance, parseDefaultAppearance };