The relevant TrueType font is missing both /ToUnicode *and* /Encoding entires, either of which would have prevented the (current) broken textLayer rendering.
My first idea was that we could use the `post` table in the TrueType font, see https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6post.html, to get the actual glyphNames and amend the fallback ToUnicode-map that way. Unfortunately that didn't work, since the `post` table only contained ".notdef" and "" (i.e. empty string) entries.
Instead we try to use the `name` table in the TrueType font, see https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6name.html, to determine if the platform is Windows and thus fallback to generate a ToUnicode-map from the `WinAnsiEncoding`.
This fixes a warning reported by CodeQL, and should also make general sense given that we parse the font-data to determine the *actual* `type`/`subtype` rather than trusting the PDF document.
This was deprecated in PR 15758 and given that it's quite unlikely that any third-party users are relying on this functionality, since it was only ever added to support telemetry reporting in the Firefox PDF Viewer, it should hopefully be fine to remove this fairly quickly.
These changes reduce the bundle size of the Firefox PDF Viewer by 4.5 kB in total.
- For text fields
* when printing, we generate a fake font which contains some widths computed thanks to
an OffscreenCanvas and its method measureText.
In order to avoid to have to layout the glyphs ourselves, we just render all of them
in one call in the showText method in using the system sans-serif/monospace fonts.
* when saving, we continue to create the appearance streams if the fonts contain the char
but when a char is missing, we just set, in the AcroForm dict, the flag /NeedAppearances
to true and remove the appearance stream. This way, we let the different readers handle
the rendering of the strings.
- For FreeText annotations
* when printing, we use the same trick as for text fields.
* there is no need to save an appearance since Acrobat is able to infer one from the
Content entry.
The purpose of this patch is twofold:
- Initialize the unicode-category data *lazily* during text-extraction, since this is completely unused during general parsing/rendering.
- Stop exposing this data in the API, since it's unused on the main-thread and it seems like it was *accidentally* included.
Obviously these changes are API-observable, but hopefully no user is depending on this. Furthermore, it's trivial for a user to re-create this unicode-category data manually with a regular expression (from the exposed `unicode` property).
Currently, during text-extraction, we're repeatedly normalizing and (when necessary) reversing the unicode-values every time. This seems a little unnecessary, since the result won't change, hence this patch moves that into the `Glyph`-instance and makes it *lazily* initialized.
Taking the `tracemonkey.pdf` document as an example: When extracting the text-content there's a total of 69236 characters but only 595 unique `Glyph`-instances, which mean a 99.1 percent cache hit-rate. Generally speaking, the longer a PDF document is the more beneficial this should be.
*Please note:* The old code is fast enough that it unfortunately seems difficult to measure a (clear) performance improvement with this patch, so I completely understand if it's deemed an unnecessary change.
With the changes in the previous patch we can move the glyph-cache lookup to the top of the method and thus avoid a bunch of, in *almost* every case, completely unnecessary re-parsing for every `charCode`.
This method, and its class, was originally added in PR 4453 to reduce memory usage when parsing text. Then PR 13494 extended the `Glyph`-representation slightly to also include the `charCode`, which made the `matchesForCache` method *effectively* redundant since most properties on a `Glyph`-instance indirectly depends on that one. The only exception is potentially `isSpace` in multi-byte strings.
Also, something that I noticed when testing this code: The `matchesForCache` method never worked correctly for `Glyph`s containing `accent`-data, since Objects are passed by reference in JavaScript. For affected fonts, of which there's only a handful of examples in our test-suite, we'd fail to find an already existing `Glyph` because of this.
Most of the `String.prototype.search` call-sites found throughout the code-base is actually not necessary, since we usually only want a *boolean*, and those can be replaced with `RegExp.prototype.test` instead.
Given that the change in PR 13393 was slightly speculative, given the lack of test-cases, let's just revert part of that to fix the referenced issue.
Based on a quick look at old issues and existing test-cases, it seems that most (if not all) PDF documents that benefit from using the font-data in this way lack any /ToUnicode maps which should mean that they're unaffected by these changes.
When there are *multiple* empty glyphs at the start of the data, ensure that the "first" glyph gets a correct `endOffset` to avoid skipping it during parsing in the `sanitizeGlyph` function.
The call-sites are replaced by direct `typeof`-checks instead, which removes unnecessary function calls. Note that in the `src/`-folder we already had more `typeof`-cases than `isNum`-calls.
These changes were *mostly* done using regular expression search-and-replace, with two exceptions:
- In `Font._charToGlyph` we no longer unconditionally update the `width`, since that seems completely unnecessary.
- In `PDFDocument.documentInfo`, when parsing custom entries, we now do the `typeof`-check once.
- it aims to fix#14502 and bug 1721335;
- Acrobat and Pdfium do the same;
- it'll avoid to have truncated data when printed;
- change the factor to compute font size in using field height: lineHeight = 1.35*fontSize
- this is the value used by Acrobat.
- in order to not have truncated strings on the bottom, add few basic metrics for standard fonts.
If a PDF included an embedded TrueType font whose preferred character
map (cmap) was in "format 2", the code would select that character map
and then refuse to read it because of an unsupported format, thus
causing the characters not to be rendered. This commit implements
support for format 2 as described at the link below.
https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6cmap.html
In the referenced bug, the embedded fonts contain custom CMap-data that only include strings. Note how for embedded composite TrueType fonts we're using the CMap-data when building the glyph mapping, and currently we end up with a completely empty map because the code expects only CID *numbers*.
Furthermore, just fixing the glyph mapping alone isn't sufficient to fully address the bug, since we also need to consider this "special" kind of CMap-data when looking up glyph widths.
*This is similar to the "isSymbolicFont"-property, which is no longer exported by default after PR 11777.*
Both "isMonospace" and "isSerifFont" are internal properties, used during font parsing and building of the glyph mapping on the worker-thread.
However both of these properties are completely unused on the main-thread and/or in the API, and accessing them they will now require setting the `fontExtraProperties`-option when calling `getDocument`.
Currently we only exclude /Encoding entries that also contains a /Differences array, which is the cause of the text-selection problem in the referenced issue.
In order to address this we'll now also exclude /Encoding entries that contain one of the predefined *named* encodings, and no longer require that it also contains a /Differences array.
*Please note:* This patch cases a small "regression" in the `bug1130815-text` test-case, however this is actually an improvement when compared with Adobe Reader and PDFium (in Google Chrome).
This reduces some unnecessary duplication, since we currently have essentially the same code in a handful of places in the `Font.fallbackToSystemFont`-method.
*Please note:* All of this feels very handwavy, but at least it passes all tests locally. Hopefully we have enough tests for this part of the font code.
For non-embedded composite standard fonts with an "incomplete" /CIDToGIDMap, we'll now fallback to an *explicitly defined* /ToUnicode map even when that one happens to be an /Identity-H or /Identity-V map.
The `Font.fallbackToSystemFont` method is unfortunately getting more and more special-cases, however that might be unavoidable given all the weird non-embedded fonts found in the wild :-(
In the PDF document some of the glyphs have bogus `differences`-entries[1] that cannot be resolved to valid glyph names, thus causing the glyph mapping to fail.
My initial idea was to use a similar approach as in the `PartialEvaluator._simpleFontToUnicode`-method, to extract the charCodes from those entries, however it turned out that that didn't actually help in this case (the mapping was still wrong).
To fix this I'm thus proposing that we fallback to the /ToUnicode map when no other useable data exists (e.g. no post-table), since it *hopefully* shouldn't make things any worse than leaving parts of the glyph map empty (which currently happens).
---
[1] As can be seem below, some of the entries are completely normal while others are non-standard:
```
Differences (array)
0 = 65
1 = /g5167
2 = /space
3 = /g11927
4 = /g17737
5 = /g11540
6 = /g2180
7 = /K
8 = /P
9 = /two
10 = /zero
11 = /one
12 = /five
13 = /four
14 = /g6932
15 = /g7246
16 = /g1691
17 = /g2343
18 = /g14792
19 = /g3325
20 = /g4280
21 = /g20383
22 = /g18166
23 = /g16988
24 = /g17943
25 = /g19223
26 = /g10830
27 = 97
28 = /g982
29 = /g1226
30 = /g5059
31 = /g2677
32 = /g1042
33 = /g11568
34 = /L
35 = /three
36 = /seven
37 = /g2364
38 = /g12063
39 = /g5356
40 = /g2173
41 = /g17877
42 = /g7273
43 = /g7647
44 = /g7224
45 = /g19327
46 = /g5054
47 = /g2342
48 = /g10136
49 = /g6856
50 = /g13381
51 = /g7257
52 = /g12093
53 = /g2359
```
- All the scale factors in for the substitution font were wrong because of different glyph positions between Liberation and the other ones:
- regenerate all the factors
- Text may have polish chars for example and in this case the glyph widths were wrong:
- treat substitution font as a composite one
- add a map glyphIndex to unicode for Liberation in order to generate width array for cid font
- In order to better compute text fields size, use line height with no gaps (and consequently guessed height for text are slightly better in general).
- Fix default background color in fields.
- font line height is taken into account by acrobat when it isn't with masterpdfeditor: I extracted a font from a pdf, modified some ascent/descent properties thanks to ttx and the reinjected the font in the pdf: only Acrobat is taken it into account. So in this patch, line heights for some substituted fonts are added.
- it seems that Acrobat is using a line height of 1.2 when the line height in the font is not enough (it's the only way I found to fix correctly bug 1718741).
- don't use flex in wrapper container (which was causing an horizontal overflow in the above bug).
- consequently, the above fixes introduced a lot of small regressions, so in order to see real improvements on reftests, I fixed the regressions in this patch:
- replace margin by padding in some case where padding is a part of a container dimensions;
- remove some flex display: some containers are wrongly sized when rendered;
- set letter-spacing to 0.01px: it helps to be sure that text is not broken because of not enough width in Firefox.
According to a comment in `readCmapTable`, we're assuming that the cmap tables (when more than one exist) are sorted in ascending order. If that's not the case, keep checking the following cmap tables in order to fix the referenced issue.
- partial fix for https://bugzilla.mozilla.org/show_bug.cgi?id=1716980;
- some pdf can contain an invalid font family (e.g. 'Windings 3') so in this case remove the space;
- the font family in typeface attribute doesn't always match the one defined in the FontDescriptor dictionary.
- some containers doesn't always have their 2 dimensions and those dimensions re based on contents;
- so in order to measure text, we must get the glyph widths (for the xfa fonts) before starting the layout;
- implement a word-wrap algorithm;
- handle font change during text layout.
Rather than having to create and check a *separate* `ToUnicodeMap` to handle these cases, we can simply use the `fallbackToUnicode`-data (when it exists) to directly supplement *missing* /ToUnicode entires in the regular `ToUnicodeMap` instead.
Note that all standard Encodings have the same length (i.e. `256` elements) and that missing entries are always represented by empty strings, hence why a separate exists-check isn't necessary in the `baseEncoding` case.
*This is somewhat similiar to the recent changes, in PR 13277, for fonts with an /Encoding entry.*
Currently we're *completely* ignoring the `builtInEncoding`, from the font data itself, for fonts which have a built-in /ToUnicode map.
While it (obviously) doesn't seem like a good idea in general to simply overwrite existing built-in /ToUnicode entries, it should however not hurt to use the `builtInEncoding` to supplement *missing* /ToUnicode entires.
- a lot of xfa files are using Myriad pro or Arial fonts without embedding them and some containers have some dimensions based on those font metrics. So not having the exact same font leads to a wrong display.
- since it's pretty hard to find a replacement font with the exact same metrics, this patch gives the possibility to read glyf table, rescale each glyph and then write a new table.
- so once PR #12726 is merged we could rescale for example Helvetica to replace Myriad Pro.
