The existing code is unable to *correctly* extract the color from the appearance-stream when the ColorSpace-data is "complex". To reproduce this:
- Open `freetexts.pdf` in the viewer.
- Note the purple color of the "Hello World from Preview" annotation.
- Enable any of the Editors.
- Note how the relevant annotation is now black.
Currently the `fontName`-property contains an actual /Name-instance, which is a problem given that its fallback value is an empty string; see ca7f546828/src/core/default_appearance.js (L35)
The reason that this is a problem can be seen in ca7f546828/src/core/primitives.js (L30-L34), since an empty string short-circuits the cache. Essentially, in PDF documents, a /Name-instance cannot be empty and the way that the `DefaultAppearanceEvaluator` does things is unfortunately not entirely correct.
Hence the `fontName`-property is changed to instead contain a string, rather than a /Name-instance, which simplifies the code overall.
*Please note:* I'm tagging this patch with "[api-minor]", since PR 12831 is included in the current pre-release (although we're not using the `fontName`-property in the display-layer).
Note how, in the `if (this.stateManager.stateStack.length !== 0) {` branch, we're attempting to access the not yet defined variable[1] `args`. If this code-path is ever hit, an Error will be thrown and parsing will thus be aborted immediately (likely leading to e.g. rendering bugs).
Note that I found this purely by accident, since I happened to glance at the LGTM report. However, I've since found that the error is also present during the unit-test[2] and with this patch we're actually testing the *intended* thing here.
As part of fixing this, and to avoid re-introducing a similar bug in the future, we'll now instead always reset `args.length` *before* attempting to read the next operator.
Also, we can use the existing `EvaluatorPreprocessor.savedStatesDepth` getter to simplify the save/restore detection a tiny bit.
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[1] The ESLint rule `no-use-before-define` would have helped catch this problem, but unfortunately we cannot enable that without quite a bit of refactoring all over the code-base.
[2] The unit-test was updated such that it would fail in the `master`-branch.
* Add a parser to get font data from the default appearance
- pdfium & poppler use a special parser too to get these info.
* Update src/core/default_appearance.js
Co-authored-by: Jonas Jenwald <jonas.jenwald@gmail.com>
Co-authored-by: Jonas Jenwald <jonas.jenwald@gmail.com>
