The purpose of PR 11844 was to reduce memory usage once fonts have been attached to the DOM, since the font-data can be quite large in many cases.
Unfortunately the new `clearData` method added in PR 20197 doesn't actually remove *anything*, it just replaces the font-data with zeros which doesn't help when the underlying `ArrayBuffer` itself isn't modified.
The method does include a commented-out `resize` call[1], but uncommenting that just breaks rendering completely.
To address this regression, without having to make large or possibly complex changes, this patch simply changes the `clearData` method to replace the internal buffer/view with its contents *before* the font-data.
While this does lead to a data copy, the size of this data is usually orders of magnitude smaller than the font-data that we're removing.
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[1] Slightly off-topic, but I don't think that patches should include commented-out code since there's a very real risk that those things never get found/fixed.
At the very least such cases should be clearly marked with `// TODO: ...` comments, and should possibly also have an issue filed about fixing the TODO.
Follow up on https://github.com/mozilla/pdf.js/pull/20197,
This serializes pattern data into an ArrayBuffer which is
then transferred from the worker to the main thread.
It sets up the stage for us to eventually switch to a
SharedArrayBuffer in the future.
This PR serializes font data into an ArrayBuffer
that is then transfered from the worker to the
main thread. It's more efficient than the current
solution which clones the "export data" object
which includes the font data as a Uint8Array.
It prepares us to switch to a SharedArrayBuffer
in the future, which would allow us to share
the font data with multiple agents, which would be
crucial for the upcoming "renderer" worker.
