f90f9466e3
Following the STR in the issue, this patch reduces the number of `PartialEvaluator.getTextContent`-related `postMessage`-calls by approximately 78 percent.[1]
Note that by enforcing a relatively low value when batching text chunks, we should thus improve worst-case scenarios while not negatively affect all `textLayer` building.
While working on these changes I noticed, thanks to our unit-tests, that the implementation of the `appendEOL` function unfortunately means that the number and content of the textItems could actually be affected by the particular chunking used.
That seems *extremely* unfortunate, since in practice this means that the particular chunking used is thus observable through the API. Obviously that should be a completely internal implementation detail, which is why this patch also modifies `appendEOL` to mitigate that.[2]
Given that this patch adds a *minimum* batch size in `enqueueChunk`, there's obviously nothing preventing it from becoming a lot larger then the limit (depending e.g. on the PDF structure and the CPU load/speed).
While sending more text chunks at once isn't an issue in itself, it could become problematic at the main-thread during `textLayer` building. Note how both the `PartialEvaluator` and `CanvasGraphics` implementations utilize `Date.now()`-checks, to prevent long-running parsing/rendering from "hanging" the respective thread. In the `textLayer` building we don't utilize such a construction[3], and streaming of textContent is thus essentially acting as a *simple* stand-in for that functionality.
Hence why we want to avoid choosing a too large minimum batch size, since that could thus indirectly affect main-thread performance negatively.
---
[1] While it'd be possible to go even lower, that'd likely require more invasive re-factoring/changes to the `PartialEvaluator.getTextContent`-code to ensure that the batches don't become too large.
[2] This should also, as far as I can tell, explain some of the regressions observed in the "enhance" text-selection tests back in PR 13257.
Looking closer at the `appendEOL` function it should potentially be changed even more, however that should probably not be done here.
[3] I'd really like to avoid implementing something like that for the `textLayer` building as well, given that it'd require adding a fair bit of complexity.
PDF.js 
PDF.js is a Portable Document Format (PDF) viewer that is built with HTML5.
PDF.js is community-driven and supported by Mozilla. Our goal is to create a general-purpose, web standards-based platform for parsing and rendering PDFs.
Contributing
PDF.js is an open source project and always looking for more contributors. To get involved, visit:
- Issue Reporting Guide
- Code Contribution Guide
- Frequently Asked Questions
- Good Beginner Bugs
- Projects
Feel free to stop by our Matrix room for questions or guidance.
Getting Started
Online demo
Please note that the "Modern browsers" version assumes native support for
features such as e.g. async/await, ReadableStream, optional chaining, and
nullish coalescing.
-
Modern browsers: https://mozilla.github.io/pdf.js/web/viewer.html
-
Older browsers: https://mozilla.github.io/pdf.js/legacy/web/viewer.html
Browser Extensions
Firefox
PDF.js is built into version 19+ of Firefox.
Chrome
- The official extension for Chrome can be installed from the Chrome Web Store. This extension is maintained by @Rob--W.
- Build Your Own - Get the code as explained below and issue
gulp chromium. Then open Chrome, go toTools > Extensionand load the (unpackaged) extension from the directorybuild/chromium.
Getting the Code
To get a local copy of the current code, clone it using git:
$ git clone https://github.com/mozilla/pdf.js.git
$ cd pdf.js
Next, install Node.js via the official package or via nvm. You need to install the gulp package globally (see also gulp's getting started):
$ npm install -g gulp-cli
If everything worked out, install all dependencies for PDF.js:
$ npm install
Finally, you need to start a local web server as some browsers do not allow opening
PDF files using a file:// URL. Run:
$ gulp server
and then you can open:
Please keep in mind that this requires a modern and fully up-to-date browser; refer to Building PDF.js for non-development usage of the PDF.js library.
It is also possible to view all test PDF files on the right side by opening:
Building PDF.js
In order to bundle all src/ files into two production scripts and build the generic
viewer, run:
$ gulp generic
If you need to support older browsers, run:
$ gulp generic-legacy
This will generate pdf.js and pdf.worker.js in the build/generic/build/ directory (respectively build/generic-legacy/build/).
Both scripts are needed but only pdf.js needs to be included since pdf.worker.js will
be loaded by pdf.js. The PDF.js files are large and should be minified for production.
Using PDF.js in a web application
To use PDF.js in a web application you can choose to use a pre-built version of the library
or to build it from source. We supply pre-built versions for usage with NPM and Bower under
the pdfjs-dist name. For more information and examples please refer to the
wiki page on this subject.
Including via a CDN
PDF.js is hosted on several free CDNs:
- https://www.jsdelivr.com/package/npm/pdfjs-dist
- https://cdnjs.com/libraries/pdf.js
- https://unpkg.com/pdfjs-dist/
Learning
You can play with the PDF.js API directly from your browser using the live demos below:
More examples can be found in the examples folder. Some of them are using the pdfjs-dist package, which can be built and installed in this repo directory via gulp dist-install command.
For an introduction to the PDF.js code, check out the presentation by our contributor Julian Viereck:
More learning resources can be found at:
The API documentation can be found at:
Questions
Check out our FAQs and get answers to common questions:
Talk to us on Matrix:
File an issue:
Follow us on twitter: @pdfjs