pdf.js/web/text_layer_builder.js

/* -*- Mode: Java; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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.
 */
/* globals CustomStyle, PDFFindController, scrollIntoView, PDFJS */

'use strict';

var FIND_SCROLL_OFFSET_TOP = -50;
var FIND_SCROLL_OFFSET_LEFT = -400;
var MAX_TEXT_DIVS_TO_RENDER = 100000;
var RENDER_DELAY = 200; // ms

/**
 * TextLayerBuilder provides text-selection functionality for the PDF.
 * It does this by creating overlay divs over the PDF text. These divs
 * contain text that matches the PDF text they are overlaying. This object
 * also provides a way to highlight text that is being searched for.
 */
var TextLayerBuilder = function textLayerBuilder(options) {
  this.textLayerDiv = options.textLayerDiv;
  this.layoutDone = false;
  this.divContentDone = false;
  this.pageIdx = options.pageIndex;
  this.matches = [];
  this.lastScrollSource = options.lastScrollSource || null;
  this.viewport = options.viewport;
  this.isViewerInPresentationMode = options.isViewerInPresentationMode;
  this.textDivs = [];

  if (typeof PDFFindController === 'undefined') {
    window.PDFFindController = null;
  }

  this.renderLayer = function textLayerBuilder_renderLayer() {
    var textLayerFrag = document.createDocumentFragment();
    var textDivs = this.textDivs;
    var textDivsLength = textDivs.length;
    var canvas = document.createElement('canvas');
    var ctx = canvas.getContext('2d');

    // No point in rendering many divs as it would make the browser
    // unusable even after the divs are rendered.
    if (textDivsLength > MAX_TEXT_DIVS_TO_RENDER) {
      return;
    }

    for (var i = 0; i < textDivsLength; i++) {
      var textDiv = textDivs[i];
      if (textDiv.dataset.isWhitespace !== undefined) {
        continue;
      }

      ctx.font = textDiv.style.fontSize + ' ' + textDiv.style.fontFamily;
      var width = ctx.measureText(textDiv.textContent).width;
      if (width > 0) {
        textLayerFrag.appendChild(textDiv);
        var textScale = textDiv.dataset.canvasWidth / width;
        var rotation = textDiv.dataset.angle;
        var transform = 'scale(' + textScale + ', 1)';
        transform = 'rotate(' + rotation + 'deg) ' + transform;
        CustomStyle.setProp('transform' , textDiv, transform);
        CustomStyle.setProp('transformOrigin' , textDiv, '0% 0%');
      }
    }

    this.textLayerDiv.appendChild(textLayerFrag);
    this.renderingDone = true;
    this.updateMatches();
  };

  this.setupRenderLayoutTimer =
    function textLayerBuilder_setupRenderLayoutTimer() {
    // Schedule renderLayout() if the user has been scrolling,
    // otherwise run it right away.
    var self = this;
    var lastScroll = (this.lastScrollSource === null ?
                      0 : this.lastScrollSource.lastScroll);

    if (Date.now() - lastScroll > RENDER_DELAY) { // Render right away
      this.renderLayer();
    } else { // Schedule
      if (this.renderTimer) {
        clearTimeout(this.renderTimer);
      }
      this.renderTimer = setTimeout(function() {
        self.setupRenderLayoutTimer();
      }, RENDER_DELAY);
    }
  };

  this.appendText = function textLayerBuilder_appendText(geom, styles) {
    var style = styles[geom.fontName];
    var textDiv = document.createElement('div');
    this.textDivs.push(textDiv);
    if (!/\S/.test(geom.str)) {
      textDiv.dataset.isWhitespace = true;
      return;
    }
    var tx = PDFJS.Util.transform(this.viewport.transform, geom.transform);
    var angle = Math.atan2(tx[1], tx[0]);
    if (style.vertical) {
      angle += Math.PI / 2;
    }
    var fontHeight = Math.sqrt((tx[2] * tx[2]) + (tx[3] * tx[3]));
    var fontAscent = (style.ascent ? style.ascent * fontHeight :
      (style.descent ? (1 + style.descent) * fontHeight : fontHeight));

    textDiv.style.position = 'absolute';
    textDiv.style.left = (tx[4] + (fontAscent * Math.sin(angle))) + 'px';
    textDiv.style.top = (tx[5] - (fontAscent * Math.cos(angle))) + 'px';
    textDiv.style.fontSize = fontHeight + 'px';
    textDiv.style.fontFamily = style.fontFamily;

    textDiv.textContent = geom.str;
    textDiv.dataset.fontName = geom.fontName;
    textDiv.dataset.angle = angle * (180 / Math.PI);
    if (style.vertical) {
      textDiv.dataset.canvasWidth = geom.height * this.viewport.scale;
    } else {
      textDiv.dataset.canvasWidth = geom.width * this.viewport.scale;
    }
  };

  this.setTextContent = function textLayerBuilder_setTextContent(textContent) {
    this.textContent = textContent;

    var textItems = textContent.items;
    for (var i = 0, len = textItems.length; i < len; i++) {
      this.appendText(textItems[i], textContent.styles);
    }
    this.divContentDone = true;
    this.setupRenderLayoutTimer();
  };

  this.convertMatches = function textLayerBuilder_convertMatches(matches) {
    var i = 0;
    var iIndex = 0;
    var bidiTexts = this.textContent.items;
    var end = bidiTexts.length - 1;
    var queryLen = (PDFFindController === null ?
                    0 : PDFFindController.state.query.length);
    var ret = [];

    for (var m = 0, len = matches.length; m < len; m++) {
      // Calculate the start position.
      var matchIdx = matches[m];

      // Loop over the divIdxs.
      while (i !== end && matchIdx >= (iIndex + bidiTexts[i].str.length)) {
        iIndex += bidiTexts[i].str.length;
        i++;
      }

      if (i === bidiTexts.length) {
        console.error('Could not find a matching mapping');
      }

      var match = {
        begin: {
          divIdx: i,
          offset: matchIdx - iIndex
        }
      };

      // Calculate the end position.
      matchIdx += queryLen;

      // Somewhat the same array as above, but use > instead of >= to get
      // the end position right.
      while (i !== end && matchIdx > (iIndex + bidiTexts[i].str.length)) {
        iIndex += bidiTexts[i].str.length;
        i++;
      }

      match.end = {
        divIdx: i,
        offset: matchIdx - iIndex
      };
      ret.push(match);
    }

    return ret;
  };

  this.renderMatches = function textLayerBuilder_renderMatches(matches) {
    // Early exit if there is nothing to render.
    if (matches.length === 0) {
      return;
    }

    var bidiTexts = this.textContent.items;
    var textDivs = this.textDivs;
    var prevEnd = null;
    var isSelectedPage = (PDFFindController === null ?
      false : (this.pageIdx === PDFFindController.selected.pageIdx));
    var selectedMatchIdx = (PDFFindController === null ?
                            -1 : PDFFindController.selected.matchIdx);
    var highlightAll = (PDFFindController === null ?
                        false : PDFFindController.state.highlightAll);
    var infinity = {
      divIdx: -1,
      offset: undefined
    };

    function beginText(begin, className) {
      var divIdx = begin.divIdx;
      textDivs[divIdx].textContent = '';
      appendTextToDiv(divIdx, 0, begin.offset, className);
    }

    function appendTextToDiv(divIdx, fromOffset, toOffset, className) {
      var div = textDivs[divIdx];
      var content = bidiTexts[divIdx].str.substring(fromOffset, toOffset);
      var node = document.createTextNode(content);
      if (className) {
        var span = document.createElement('span');
        span.className = className;
        span.appendChild(node);
        div.appendChild(span);
        return;
      }
      div.appendChild(node);
    }

    var i0 = selectedMatchIdx, i1 = i0 + 1;
    if (highlightAll) {
      i0 = 0;
      i1 = matches.length;
    } else if (!isSelectedPage) {
      // Not highlighting all and this isn't the selected page, so do nothing.
      return;
    }

    for (var i = i0; i < i1; i++) {
      var match = matches[i];
      var begin = match.begin;
      var end = match.end;
      var isSelected = (isSelectedPage && i === selectedMatchIdx);
      var highlightSuffix = (isSelected ? ' selected' : '');
     
      if (isSelected && !this.isViewerInPresentationMode) {
        scrollIntoView(textDivs[begin.divIdx],
                       { top: FIND_SCROLL_OFFSET_TOP,
                         left: FIND_SCROLL_OFFSET_LEFT });
      }

      // Match inside new div.
      if (!prevEnd || begin.divIdx !== prevEnd.divIdx) {
        // If there was a previous div, then add the text at the end.
        if (prevEnd !== null) {
          appendTextToDiv(prevEnd.divIdx, prevEnd.offset, infinity.offset);
        }
        // Clear the divs and set the content until the starting point.
        beginText(begin);
      } else {
        appendTextToDiv(prevEnd.divIdx, prevEnd.offset, begin.offset);
      }

      if (begin.divIdx === end.divIdx) {
        appendTextToDiv(begin.divIdx, begin.offset, end.offset,
                        'highlight' + highlightSuffix);
      } else {
        appendTextToDiv(begin.divIdx, begin.offset, infinity.offset,
                        'highlight begin' + highlightSuffix);
        for (var n0 = begin.divIdx + 1, n1 = end.divIdx; n0 < n1; n0++) {
          textDivs[n0].className = 'highlight middle' + highlightSuffix;
        }
        beginText(end, 'highlight end' + highlightSuffix);
      }
      prevEnd = end;
    }

    if (prevEnd) {
      appendTextToDiv(prevEnd.divIdx, prevEnd.offset, infinity.offset);
    }
  };

  this.updateMatches = function textLayerBuilder_updateMatches() {
    // Only show matches when all rendering is done.
    if (!this.renderingDone) {
      return;
    }

    // Clear all matches.
    var matches = this.matches;
    var textDivs = this.textDivs;
    var bidiTexts = this.textContent.items;
    var clearedUntilDivIdx = -1;

    // Clear all current matches.
    for (var i = 0, len = matches.length; i < len; i++) {
      var match = matches[i];
      var begin = Math.max(clearedUntilDivIdx, match.begin.divIdx);
      for (var n = begin, end = match.end.divIdx; n <= end; n++) {
        var div = textDivs[n];
        div.textContent = bidiTexts[n].str;
        div.className = '';
      }
      clearedUntilDivIdx = match.end.divIdx + 1;
    }

    if (PDFFindController === null || !PDFFindController.active) {
      return;
    }

    // Convert the matches on the page controller into the match format
    // used for the textLayer.
    this.matches = this.convertMatches(PDFFindController === null ?
      [] : (PDFFindController.pageMatches[this.pageIdx] || []));
    this.renderMatches(this.matches);
  };
};