In PR 11912 we started caching images that occur on multiple pages globally, which improved performance a lot in many PDF documents.
However, one slightly annoying limitation of the implementation is the need to re-parse the image once the global-caching threshold has been reached. Previously this was difficult to avoid, since large image-resources will cause cleanup to run on the main-thread after rendering has finished. In PR 16108 we started delaying this cleanup a little bit, to improve performance if a user e.g. zooms and/or rotates the document immediately after rendering completes.
Taking those two PRs together, we now have a situation where it's much more likely that the main-thread has "globally used" images cached at the page-level. Hence we can instead attempt to *copy* a locally cached image into the global object-cache on the main-thread and thus reduce unnecessary re-parsing of large/complex global images, which significantly reduces the rendering time in many cases.
For the PDF document in issue 11878, the rendering time of *the second page* changes as follows (on my computer):
- With the `master`-branch it takes >600 ms to render.
- With this patch that goes down to ~50 ms, which is one order of magnitude faster.
(Note that all other pages are, as expected, completely unaffected by these changes.)
This new main-thread copying is limited to "large" global images, since:
- Re-parsing of small images, on the worker-thread, is usually fast enough to not be an issue.
- With the delayed cleanup after rendering, it's still not guaranteed that an image is available in a page-level cache on the main-thread.
- This forces the worker-thread to wait for the main-thread, which is a pattern that you always want to avoid unless absolutely necessary.
This commit changes the code to use a template string and to use `const`
instead of `var`. Combined with the previous commits this allows for
enabling the ESLint `no-var` rule for this file now.
The test helper code largely predates the introduction of modern
JavaScript features and should be refactored to improve readability.
In particular callbacks make the code harder to understand and maintain.
This commit:
- replaces the callback argument with returning a promise;
- replaces the recursive function calls with a simple loop;
- uses `const`/`let` instead of `var`;
- uses arrow functions for shorter code;
- uses template strings for shorter string formatting code.
The test helper code largely predates the introduction of modern
JavaScript features and should be refactored to improve readability.
In particular callbacks make the code harder to understand and maintain.
This commit:
- replaces the callback argument with returning a promise;
- uses `const` instead of `var`;
- uses arrow functions for shorter code;
- uses template strings for shorter string formatting code;
- uses `Array.includes` for shorter response code checking code.
This test intermittently fails, likely because the auto-print is triggered fast enough
that we don't manage to get it.
So this patch aims to try to set a listener very early in order to be sure that
we'll be aware that a print has been triggered.
It seems this unit-test now fails consistently in "all" up-to-date Node.js versions. We should probably try and understand why, but for now just disable it to get passing CI tests.
There's obviously a few things wrong with the Annotations in the referenced PDF document, however parsing of an Annotation shouldn't just break if the /BS-entry isn't a dictionary.
