GSoC/2019/StatusReports/JoãoNetto

Improving Okular JavaScript Support

Adobe defines a set of JavaScript functions in its JavaScript for Adobe API reference. Our plan is to support the execution of these scripts by the documents opened in Okular.

Work report

Supporting Animated PDF

Implementation

There is two LaTeX libraries that are able to produce animations, both use timers and JavaScript to do the frame switching needed for the animation, namely, the animate and TikZ beamer package.

For supporting the animate package, I had to modify Poppler to support changing the Forms AP stream. This AP stream is what says to Poppler what and where to render.

Then, to support the animation of a PDF we need to support the JavaScript functions are executed when certain actions are performed. The first thing done to support this was editing the code when a page is opened to execute the Widget opening script. This script was already given by Poppler, I only made Okular execute it.

Other features that were implemented:

Display - This feature defines if the form is visible and printable, there are four combinations defined in the API reference with these flags.

OCGs - These are the Optional Content Group of the PDF, or the layers, basically you can alter then to be visible or invisible and it will render different things on the PDF, they are already supported by Okular, I just made the JavaScript tap into these already existing features and using them.

Interval Functions - The base of the animation is to execute some actions in some pre defined interval, gladly we had QTimer to support this, I implemented them with a connection to execute the script given.