The following are some highlights of this patch:
- In the Worker we only extract a *subset* of the potential contents of the `Usage` dictionary, to avoid having to implement/test a bunch of code that'd be completely unused in the viewer.
- In order to still allow the user to *manually* override the default visible layers in the viewer, the viewable/printable state is purposely *not* enforced during initialization in the `OptionalContentConfig` constructor.
- Printing will now always use the *default* visible layers, rather than using the same state as the viewer (as was the case previously).
This ensures that the printing-output will correctly take the `Usage` dictionary into account, and in practice toggling of visible layers rarely seem to be necessary except in the viewer itself (if at all).[1]
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[1] In the unlikely case that it'd ever be deemed necessary to support fine-grained control of optional content visibility during printing, some new (additional) UI would likely be needed to support that case.
The fact that the highlight-thickness can only be changed in "free" mode isn't really obvious visually in the toolbar, so attempt to provide at least some indication of the `disabled`-state by "dimming" the slider.
In implementing caret browsing mode in pdf.js, I didn't notice that selectstart isn't always triggered.
So this patch removes the use of selectstart and rely only on selectionchange.
In order to simplify the selection management, the selection code is moved in the AnnotationUIManager:
- it simplifies the code;
- it allows to have only one listener for selectionchange instead of having one by visible page
for selectstart.
I had to add a delay in the integration tests for highlighting (there's a comment with an explanation),
it isn't really nice, but it's the only way I found and in real life there always is a delay between
press and release.
The function caretPositionFromPoint return the position within the last visible element
and sometimes there are some elements on top of the ones in the text layer.
So the idea is to hide the visible elements which aren't in the text layer in order
to get the right caret position.
*Please note:* This is a micro optimization, hence I fully understand if the patch is rejected.
Currently we create two temporary Arrays and have to iterate twice in total when building the final `hexNumbers` Array.
With this patch there's only one temporary Array and a single iteration required to build the final `hexNumbers` Array.
When highlighting, the annotation editor layer is disabled to get pointer events
from the text layer, but the annotation layer must be then disabled either in
order to avoid bad interactions.
As part of the changes in PR 17686 we "accidentally" enabled source-maps for the *minified* builds, which seems unnecessary since those have never been included in the `pdfjs-dist` output.
Locally this patch reduces the run-time of `gulp minified` by ~15 percent.
Rather than first building the library and then use Terser "manually" to minify the files, we can utilize a Webpack plugin to combine these steps which helps to simplify the gulpfile.
