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Build a fallback ToUnicode map for simple fonts (issue 8229)

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In some fonts, the included `ToUnicode` data is incomplete causing text-selection to not work properly. For simple fonts that contain encoding data, we can manually build a `ToUnicode` map to attempt to improve things.

Please note that since we're currently using the `ToUnicode` data during glyph mapping, in an attempt to avoid rendering regressions, I purposely didn't want to amend to original `ToUnicode` data for this text-selection edge-case.
Instead, I opted for the current solution, which will (hopefully) give slightly better text-extraction results in PDF file with incomplete `ToUnicode` data.

According to the PDF specification, see [section 9.10.2](http://www.adobe.com/content/dam/acom/en/devnet/acrobat/pdfs/PDF32000_2008.pdf#G8.1873172):

> A conforming reader can use these methods, in the priority given, to map a character code to a Unicode value.
> ...

Reading that paragraph literally, it doesn't seem too unreasonable to use *different* methods for different charcodes.

Fixes 8229.
This commit is contained in:
Jonas Jenwald 2017-11-26 13:29:43 +01:00
parent ffbfc3c2a7
commit 61e19bee43
5 changed files with 21 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

8
src/core/evaluator.js
View file

@ -2021,6 +2021,14 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
// Section 9.10.2 Mapping Character Codes to Unicode Values
if (properties.hasIncludedToUnicodeMap) {
// Some fonts contain incomplete ToUnicode data, causing issues with
// text-extraction. For simple fonts, containing encoding information,
// use a fallback ToUnicode map to improve this (fixes issue8229.pdf).
if (!properties.composite && properties.hasEncoding) {
properties.fallbackToUnicode =
this._buildSimpleFontToUnicode(properties);
}
return Promise.resolve(properties.toUnicode);
}

8
src/core/fonts.js
View file

@ -211,9 +211,9 @@ var Glyph = (function GlyphClosure() {
})();
var ToUnicodeMap = (function ToUnicodeMapClosure() {
function ToUnicodeMap(cmap) {
function ToUnicodeMap(cmap = []) {
// The elements of this._map can be integers or strings, depending on how
// |cmap| was created.
// `cmap` was created.
this._map = cmap;
}
@ -516,6 +516,7 @@ var Font = (function FontClosure() {
this.defaultEncoding = properties.defaultEncoding;
this.toUnicode = properties.toUnicode;
this.fallbackToUnicode = properties.fallbackToUnicode || new ToUnicodeMap();
this.toFontChar = [];
@ -2766,7 +2767,8 @@ var Font = (function FontClosure() {
width = isNum(width) ? width : this.defaultWidth;
var vmetric = this.vmetrics && this.vmetrics[widthCode];
var unicode = this.toUnicode.get(charcode) || charcode;
let unicode = this.toUnicode.get(charcode) ||
this.fallbackToUnicode.get(charcode) || charcode;
if (typeof unicode === 'number') {
unicode = String.fromCharCode(unicode);
}