A SaxonJS-based slide presentation tool.
SlidesJS presents (a specifically structured) HTML document as a series of slides, as one might display during a presentation. See, for example, the example presentation.
Given that many such tools exist, why this one? Three reasons:
- I have some specific requirements that I don’t think are met by any of the other tools.
- I’ve had a plain-old-JavaScript version of this code working for many years. We used a version of it to present a SaxonJS tutorial at Declarative Amsterdam in 2021. After that presentation, someone asked me if it was in SaxonJS.
- I thought converting it to SaxonJS would be an amusing exercise for a Friday afternoon. I was also curious about how easy it would be to integrate other JavaScript APIs into a SaxonJS application.
The most important requirement is the ability to include speaker notes on the slides and have those usefully displayed during a presentation. In other words, I want two browsers windows: one displaying the presentation for the audience and another displaying my speaker notes for the slides (on my laptop screen, for example, visible only to me). Navigation must be synchronized across the two windows.
I’ve worked out how to do this using the localStorage API.
I’ve also implemented progressive display of lists. But lots of tools can do that.
- Clone the repository.
- Edit
src/main/index.htmlreplacing the demo slide content with your own slides. Don’t change the overall structure of the HTML. - Edit
src/main/css/local.cssto add your own styles, for example the titlepage and slide background images. - Run
./gradlew publish - Arrange to serve
build/websiteover HTTP. - Open it up in your web browser.
- Profit.
Navigation between slides is done mostly with keybindings, see the online help. On touch screen devices, gestures are also supported.
The slides themselves are just HTML. You could write them by hand, or you could generate them from some other source. (I have tools to generate them from Emacs Org markup or DocBook, for example.) You can put anything you want in the slides themselves, but the top-level structure of the HTML document has to be marked up in a particular way:
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Presentation title</title> ①
<meta charset="utf-8" /> ②
<meta name="viewport" content="width=device-width, initial-scale=1, minimum-scale=1" />
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1" />
<meta name="localStorage.key" content="slidesjs" />
<meta name="timer" content="true"/>
<meta name="talk-length" content="30"/>
<script type="text/javascript" src="js/saxon-js/SaxonJS2.rt.js"></script> ③
<link rel="stylesheet" href="css/prism.css" />
<link rel="stylesheet" href="css/slides.css" />
<link rel="stylesheet" href="css/screen.css" media="screen"/>
<link rel="stylesheet" href="css/local.css" />
</head>
<body>
<main id="slidesjs_main">
<header> ④
<h1>Presentation title</h1>
<h2>If there’s a subtitle, put it here</h2>
<h3 class="date">2022-08-02</h3>
<h3 class="author">Your Name</h3>
<h3 class="conference">Conference Title</h3>
<div class="abstract">The abstract…</div>
<div class="copyright">Copyright © 2022 Your Name</div>
</header>
<div class="slide"> ⑤
<header>
<h1>First Slide Title</h1>
</header>
<!-- your slide content goes here -->
</div>
<section>
<header>
<h1>Section title</h1>
</header>
<div class="slide">
<header>
<h1>Section Slide Title</h1>
</header>
<!-- your slide content goes here -->
<aside>
<p>These are speaker notes.</p> ⑥
</aside>
</div>
</section>
<div class="slide">
<header>
<h1>Thank you</h1>
</header>
<!-- your slide content goes here -->
</div>
</main>
<div id="slidesjs_toc" class="hidden"> ⑦
</div>
<footer class="slidesjs_notes_footer">
<span id="slidesjs_time"></span>
<span id="slidesjs_message"></span>
<span id="slidesjs_time_reset"></span>
</footer>
<footer>
<div class="left">
<nav id="slidesjs_nav">
</nav>
<div id="slidesjs_copyright" class="copyright"></div>
</div>
<div id="slidesjs_pageno" class="pageno"></div>
</footer>
<script type="text/javascript" src="js/prism.js"></script> ⑧
<script type="text/javascript" src="js/start.js"></script>
</body>
</html>
Notes:
- ①
- You should change the presentation title.
- ②
- Page metadata; you can change some of these, see [metadata](#Metadata).
- ③
- Script and style links; you shouldn’t change these, though it’s fine to edit `local.css` or add your own CSS.
- ④
- The `body` must begin with a `main` that has the `id` shown, that must contain a `header`. The title is in the `h1`, an optional subtitle in an `h2`, and additional details in `h3` elements. If you want different kinds of headers, you’ll have to edit `src/main/xslt/slides.xsl` to display them.
- ⑤
- After the `header`, your `main` must contain one or more sections or slides. A section is just a `section` element; a slide is a `div` with the class `slide`. If you use sections, each section must contain one or more slides. Nested sections are not supported. Each section and slide must contain a `header` with the title in an `h1`.
- ⑥
- If you wish to add speaker notes, they go in one or more `aside` elements directly inside the slide `div`.
- ⑦
- The `div` and `footer` elements are used by the presentation, do not change or remove them.
- ⑧
- The Prism script is optioal, but you must not remove the the `start.js` script!
If you mark a list (ul or ol) with the class progressive, then the items in that list can be progressively
revealed.
By default the Prism syntax highlighter is included. You can swap it out for a different highlighter by changing the script and CSS links.
Prism, and I expect many other JavaScript syntax highlighters, work by running some code when the page is loaded. SaxonJS is dynamically changing the page, so that approach won’t work.
To manage highlighting, the stylesheet calls a forceHighlight
function after each slide is rendered. You will probably need to
change the forceHighlight function in js/start.js if you
change the syntax highlighter.
(Aside: is slapping random things directly onto the window object
kosher? I don’t know, but it’s good enough for an afternoon’s hacking
on a tool that will only ever run locally with one user.)
The compiler and SaxonJS version can be configured with Gradle properties.
- saxonJsVersion
- The version of SaxonJS to use.
- xsltCompiler
- Selects the compiler; XX=the SaxonJS compiler, XJ=the SaxonJ compiler (you will need an EE license to use the Java compiler).
- saxonVersion
- The version of the SaxonJ compiler to use; only relevant if `xsltCompiler=XJ`.
Several features can be enabled by adding HTML metadata to your presentation.
If you specify a localStorage.key in the HTML metadata:
<meta name="localStorage.key" content="slidesjs" />That key will be used with the HTML local storage API to keep multiple browser windows in sync. This allows you, for example, to display the speaker notes view on one browser and the normal view on another. The browsers will remain in sync if you navigate in either of them.
If you want to have multiple, different presentations in sync simultaneously, they need to have different keys. Otherwise, the key is irrelevant.
If you specify a timer in the HTML metadata (with a value of true):
<meta name="timer" content="true"/>A timer will be displayed in the lower-left corner of the speaker
notes view. Clicking on the timer when it is running will pause
it. Clicking on it when it’s paused will start it running again.
Clicking reset (on the far right hand side
of the screen) will reset it.
If you specify the length of your talk in the HTML metadata:
<meta name="talk-length" content="30"/>A countdown timer will be displayed in the lower-left corner of the speaker view. It decrements whenever the ordinary timer is running. It will change color as the time runs out.
Specify the talk length in minutes (30 = 30 minutes), or hours and minutes (1:30 = 90 minutes).
SaxonJS runs the style.xsl transformation on the HTML. This stylesheet selects
a slide based on the slide number in the fragment identifier and displays it by replacing
the main element content with the slide. The stylesheet also registers a handler to
catch key press and click events, responding to them accordingly.
That part is straightforward SaxonJS.
The interesting part is managing the localStorage API. The browser API allows you to register a storage change event listener, but that’s not a bubbling event so we can’t capture it directly in XSLT.
My workarounds are mostly in js/start.js.
- We setup a
slidesEventQueue. Everything that the app does, it does in response to state changes added to this queue. This allows the browser window that you’re “driving” with the keyboard and the window that may be tracking changes through the local storage API to work in the same way. - We create a
manageSlidesobject. This is a mutable storage object that can be updated by bothstart.jsand the SaxonJS application. It’s initialized a little bit carefully so that reloading the page doesn’t accidentally break a running timer. - We register a plain old JavaScript event handler for the storage change event. This handler adds events to the queue.
- We register an “on hash change” event handler that tracks changes to the fragment identifier. This allows the browser back button to work as expected. Like the storage change handler, it works by adding events to the queue.
- In the stylesheet, we use
ixsl:schedule-actionto setup a template that runs every 50ms. That template inspects the contents of themanageSlidesobject and responds accordingly.
(The object is called manageSpeakerNotes because it started out as a
way of managing the presentation of speaker notes in a second browser
window. Over time, it became used for other things, but I haven’t
tried to give it a better name.)
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