GUI tools are limiting

I used to do presentations with typical slideshow software, such as OpenOffice/LibreOffice Impress, but these tools felt restricted and limiting. I need to do a lot of reorganizing and moving around, and that might mean changing things from bullet lists to headings to text to pictures and back to bullet lists over again. This happens through the whole process. I might realize something that was just a bullet point needs to be a slide, or that a set of slides for time reasons need to be shortened down to bullet points. Much of the reorganization comes from seeing what fits on one slide and what does not, and how I need to pace the presentation, and to some extent even what kinda of pictures I can find to illustrate what I try to say, and if the pictures are funny or not.

Presentation software should give you complete freedom to reorganize your presentation on every level, not only by reorganizing slides.

The solution for me and many others, is to use a text-markup language, like reStructuredText, Markdown or similar, and then use a tool that generates an HTML slide show from that.

Text-markup gives you the convenience and freedom to quickly move parts around as you like.

I chose reStructuredText, because I know it and because it has a massive feature set. When I read the documentations of other text-markup langages it was not obvious if they has the features I needed or not.

Pan, rotate and zoom

The tools that exist to make presentations from text-markup will make slideshows that has a sequence of slides from left to right. But the fashion now is to have presentations that rotate and zoom in and out. One open source solution for that is impress.js.

With impress.js you can make modern cool presentations.

But impress.js requires you to write your presentation as HTML, which is annoying, and the markup isn't flexible enough to let you quickly reorganize things from bullet points to headings etc.

You also have to position each slide separately, and if you insert a new slide in the middle, you have to reposition all the slides that follow.

Hovercraft!

So what I want is a tool that takes the power, flexibility and convenience of reStructuredText and allows me to generate pan, rotate and zoom presentations with impress.js, without having to manually reposition each slide if I reorganize a little bit of the presentation. I couldn't find one, so I made Hovercraft.

Hovercraft’s power comes from the combination of reStructuredText’s convenience with the cool of impress.js, together with a flexible and powerful solution to position the slides.

There are four ways to position slides:

Hovercraft! also includes a presenter console that will show you your notes, slide previews and the time, essential tools for any presentation.

Shortcut/Navigation Keys:

A help popup appears upon launching a presentation; it shows the keyboard shortcuts.

Parameters

hovercraft [-h] [-t TEMPLATE] [-c CSS] [-j JS] [-a] [-s] [-n] [-p PORT] <presentation> [<targetdir>]

Positional arguments:

Optional arguments:

Presenter Console

The presenter console feature is designed for showing an annotated version of the presentation on the local laptop display, while showing the presentation itself on a projector.

To use this feature, open the presentation in a browser, and press p. A new browser tab will be created, and the browser focus will switch to that tab automatically. At this point, the two tabs are linked, and the slide navigation controls will affect both tabs.

Now, you'll need to move the presenter console tab into its own browser window. With Firefox, right-click on the tab title, and click on Move Tab --> Move to New Window. With Chromium, drag the tab title down and the tab will be moved into a new browser window.

Finally, drag the presentation window onto the projector's part of the desktop, and press F11 to make the presentation fullscreen.

Built in templates

There are two templates that come with Hovercraft! One is called default and will be used unless you specify a template. This is the template you will use most of the time.

The second is called simple and right now it only lacks the Goto function. You can ignore it.

A note on terminology

Traditionally a presentation is made up of slides. Calling them "slides" is not really relevant in an impress.js context, as they can overlap and doesn't necessarily slide. The name "steps" is better, but it's also more ambiguous. Hence impress.js uses the terms "slide" and "step" as meaning the same thing, and so does Hovercraft!

Hovercraft! syntax

Presentations are reStructuredText files. If you are reading this documentation from the source code, then you are looking at a reStructuredText document already.

It's fairly simple, you underline headings to mark them as headings:

This becomes a h1
=================
And this a h2
-------------

The different ways of underlining them doesn't mean anything, instead the order of them is relevant, so the first type of underline encountered in the file will make a level 1 heading, the second type a level 2 heading and so on. In this file = is used for level 1, and - for level 2.

You can also mark text as italic or bold, with *single asterixes* or **double asterixes** respectively.

You can also have bullet lists:

* Bullet 1
  * Bullet 1.1
* Bullet 2
* Bullet 3

And numbered lists:

1. Item 1
    1.1. Item 1.1
2. Item 2
3. Item 3

You can include images:

.. image:: path/to/image.png
    :height: 600px
    :width: 800px

As you see you can also specify height and width and loads of other parameters, but they are all optional.

You can also include videos:

.. raw:: html
    <video width="100%" controls>
        <source src="./path/to/your/video.mp4" type="video/mp4">
        Your browser does not support the video element.
    </video>

or audio:

.. raw:: html
    <audio controls>
        <source src="./path/to/your/audio.mp3" type="audio/mpeg">
        Your browser does not support the audio element.
    </audio>

And you can mark text as being preformatted. You do that by ending the previous row with double colons, or have a row of double colons by itself:

::
    This code here will be preformatted
     and shown with a  monospaced font
    and    all    spaces     preserved.

If you want to add source code, you can use the code directive, and get syntax highlighting:

.. code:: python
    def some_example_code(foo):
        return foo * foo

The syntax highlighting is done by Pygments and supports lots and lots of languages.

You are also likely to want to put a title on the presentation. You do that by having a .. title:: statement before the first slide:

.. title:: This is the presentation title

That is the most important things you'll need to know about reStructuredText for making presentations. There is a lot more to know, and a lot of advanced features like links, footnotes, and more. It is in fact advanced enough so you can write a whole book in it, but for all that you need to read the documentation.

Presenter notes

To add presenter notes, that will be displayed in the presenter console, use the following syntax:

.. note::
    Here goes the presenter note.

External files

Any image file referenced in the presentation by a relative path will be copied to the target directory, keeping it's relative path to the presentation. The same goes for images or fonts referenced in any CSS files used by the presentation or the template.

Images or fonts referenced by absolute paths or URI's will not be copied.

Styling your Presentation

The css that is included by the default template are:

For this reason you want to include your own CSS to style your slides. To include a CSS file you add a :css:-field at the top of the presentation:

:css: css/presentation.css

You can also optionally specify that the css should be only valid for certain CSS media:

:css-screen,projection: css/presentation.css
:css-print: css/print.css

You can specify any number of css files in this way. You can also add one extra CSS-file via a command-line parameter:

hovercraft --css=my_extra.css presentationfile.rst outdir/

Styling the console

You can also optionally add styles to your slides that are only used when the slide is shown in the presenter console:

:css-preview: css/slidepreview.css

You can also style the presenter console itself:

:css-console: css/console.css

There are default styles that are automatic, anything you add in the file for the css-console will just be to override the existing styling.

Adding Javascript

In a similar fashion you can add Javascript files to either header or body:

:js-header: js/firstjsfile.js
:js-body: js/secondjsfile.js

You can also add one extra Javascript-file via a command-line parameter:

hovercraft --js=my_extra.js presentationfile.rst outdir/

Adding Headers and Footers

If you want static content, content that doesn't move with each slide; for example a header, footer, your company logo or a slide background pattern, then you can insert that content with the header and footer commands:

.. header::
   .. image:: images/company-logo.png
.. footer::
    "How to use Hovercraft", Yern Busfern, ImaginaryCon 2017

The header will be located in the resulting HTML before the first slide and the footer will be located after the last slide. However, they will be displayed statically on every slide, and you will have to position them with CSS. By default the header will be displayed behind the slides and the footer in front of the slides, so the header is useful for background designs and the footer for designs that should be in the foreground.

It doesn't matter where in the presentation you add these commands, I would recommend that you add them before the first slide.

Styling a specific slide

If you want to have specific styling for a specific slide, it is a good idea to give that slide a unique ID:

:id: the-slide-id

You can then style that slide specifically with:

div#the-slide-id {
    /* Custom CSS here */
}

If you don't give it a specific ID, it will get an ID based on its sequence number. And that means the slide's ID will change if you insert or remove slides that came before it, and in that case your custom stylings of that slide will stop working.

Adding a custom class to slides

If you want to apply the same style to one or more slides you may prefer adding a class to those slides instead (or in addition to) a unique ID:

:class: my-custom-class

You can then style those slides by adding CSS rules with:

.my-custom-class {
    /* Custom CSS here */
}

Adding a custom directive

If you want to use a custom docutils directive, you'll want to run hovercraft in the same process where you register your directive. For example, you can create a custom startup script like the following:

from docutils import nodes
from docutils.parsers.rst import Directive, directives
import hovercraft
class HelloWorld(Directive):
    def run(self):
        para = nodes.paragraph(text='Hello World')
        return [para]
directives.register_directive('hello-world', HelloWorld)
if __name__ == "__main__":
    cmd = ['--skip-help', 'slides.rst']
    hovercraft.main(cmd)

While creating your own directive might be daunting, it's possible to reuse useful directives from other projects. For example, you can reuse Pelican's custom code block, which adds an hl_lines option to highlight specific lines of code. To use that directive, simply add the following import to the above script:

import pelican.rstdirectives

Portable presentations

Since Hovercraft! generates HTML5 presentations, you can use any computer that has a modern browser installed to view or show the presentation. This allows you both to put up the presentation online and to use a borrowed computer for your conference or customer presentation.

When you travel you don't know what equipment you have to use when you show your presentaton, and it's surprisingly common to encounter a projector that refuses to talk to your computer. It is also very easy to forget your dongle if you have a MacBook, and there have even been cases of computers going completely black and dead when you connect them to a projector, even though all other computers seem to work fine.

The main way of making sure your presentation is portable is to try it on different browsers and different computers. But the latter can be unfeasible, not everyone has both Windows, Linux and OS X computers at home. To help make your presentations portable it is a good idea to define your own @font-face's and use them, so you are sure that the target browser will use the same fonts as you do. Hovercraft! will automatically find @font-face definitions and copy the font files to the target directory.

impress.js fields

The documentation on impress.js is contained as comments in the demo html file. It is not always very clear, so here comes a short summary for convenience.

The different data fields that impress.js will use in 0.5.3, which is the current version, are the following:

Hovercraft! specialties

Hovercraft! has some specific ways it uses reStructuredText. First of all, the reStructuredText "transition" is used to mark the separation between different slides or steps. A transition is simply a line with four or more dashes:

----

You don't have to use dashes, you can use any of the characters used to underline headings, = - ` : . ' " ~ ^ _ * + #. And just as width headings, using different characters indicates different "levels". In this way you can make a hierarchical presentation with multiple "levels" of steps. However, impress.js does not support that, so this is only useful if you make your own templates that uses another Javascript library, for example Reveal.js. If you have more than one transition level with the templates included with Hovercraft, the resulting presentation may behave strangely.

All reStructuredText fields are converted into attributes on the current tag. Most of these will typically be ignored by the rendering to HTML, but there are two places where the tags will make a difference, and that is by putting them first in the document, or first on a slide.

Any fields you put first in a document will be rendered into attributes on the main impress.js <div>. The only ones that Hovercraft! will use are data-transition-duration, skip-help, auto-console and slide-numbers.

Any fields you put first in a slide will be rendered into attributes on the slide <div>. This is used primarily to set the position/zoom/rotation of the slide, either with the data-x, data-y and other impress.js settings, or the hovercraft-path setting, more on that later.

Hovercraft! will start making the first slide when it first encounters either a transition or a header. Everything that comes before that will belong to the presentation as a whole.

A presentation can therefore look something like this:

:data-transition-duration: 2000
:skip-help: true
.. title: Presentation Title
----
This is the first slide
=======================
Here comes some text.
----
:data-x: 300
:data-y: 2000
This is the second slide
========================
#. Here we have
#. A numbered list
#. It will get correct
#. Numbers automatically

Showing lists item by item

A common feature in presentation software is to have a list that appears item by item. This is called "substeps" and is enabled by setting the substep class on the items to be shown. In Hovercraft! the easiest was to do this is to use paragraphs, since you can set the class on multiple paragraphs at once:

.. class:: substep
    This paragraph will be shown when you press <next>
    This will show on the second <next> press
    And this will be shown third

You can also set the class just on individual paragraphs, in which case all other paragraphs will be visible from the beginning:

This paragraph will always be visible
.. class:: substep
    This paragraph will be shown when you press <next>
And this paragraph will also be always visible
.. class:: substep
    And this paragraph will show second

You can also do it with bullet lists or numbered lists:

.. class:: substep
    * This is an unordered list
        * In two levels
        * One new item will be shown on every <next> press

And, as with pagarphs you can have individual control of each item. But due to the ReStructuredText syntax you can't have individual control on the first item of a list, it will always be shown from the start:

#. This will be shown when you get to this slide
   .. class:: substep
#. The second item shows only after you press <next>
#. This also will always be shown.
   .. class:: substep
#. And this will be shown after another <next> press.

Mathematical equations

If you add a math directive then hovercraft! will add a link to the MathJax CDN so that this:

.. math:: e^{i \pi} + 1 = 0

will be rendered by the MathJax javascript library. The math directive can also be used as a "role" with the equations inlined with the text flow. Note that if you use the math statement, by default the MathJax library will be loaded from the internet, meaning that your presentation will need network connectivity to work, which can be a problem when presenting and conferences, which often have bad network connectivity.

This can be solved by specifying a local copy of mathjax with the --mathjax command line.

Relative positioning

Hovercraft! gives you the ability to position slides relative to each other. You do this by starting the coordinates with "r". This will position the slide 500 pixels to the right and a thousand pixels above the previous slide:

:data-x: r500
:data-y: r-1000

Relative paths allow you to insert and remove slides and have other slides adjust automatically. It's generally the most useful way of positioning.

Automatic positioning

If you don't specify an attribute, the slide settings will be the same as the previous slide. This means that if you used relative positioning, the next slide will move the same distance.

This gives a linear movement, and your slides will end up in a straight line.

By default the movement is 1600 pixels to the right, which means that if you don't position any slides at all, you get a standard presentation where the slides will simply slide from right to left.

SVG Paths

Hovercraft! supports positioning slides along an SVG path. This is handy, as you can create a drawing in a software that supports SVG, and then copy-paste that drawings path into your presentation.

You specify the SVG path with the :hovercraft-path: field. For example:

:hovercraft-path: m275,175 v-150 a150,150 0 0,0 -150,150 z

Every following slide that does not have any explicit positioning will be placed on this path.

There are some things you need to be careful about when using SVG paths.

Relative and absolute coordinates

SVG coordinates can either be absolute, with a reference to the page origin; or relative, which is in reference to the last point. Hovercraft! can handle both, but what it can not handle very well is a mixture of them.

Specifically, if you take an SVG path that starts with a relative movement and extract that from the SVG document, you will lose the context. All coordinates later must then also be relative. If you have an absolute coordinate you then suddenly regain the context, and everything after the first absolute coordinate will be misplaced compared to the points that come before.

Most notable, the open source software "Inkscape" will mix absolute and relative coordinates, if you allow it to use relative coordinates. You therefore need to go into it's settings and uncheck the checkbox that allows you to use relative coordinates. This forces Inkscape to save all coordinates as absolute, which will work fine.

Start position

By default the start position of the path, and hence the start position of the first slide, will be whatever the start position would have been if the slide had no positioning at all. If you want to change this position then just include :data-x: or :data-y: fields. Both relative and absolute positioning will work here.

In all cases, the first m or M command of the SVG path is effectively ignored, but you have to include it anyway.

SVG transforms

SVG allows you to draw up path and then transform it. Hovercraft! has no support for these transforms, so before you extract the path you should make sure the SVG software doesn't use transforms. In Inkscape you can do this by the "Simplify" command.

Other SVG shapes

Hovercraft! doesn't support other SVG shapes, just the path. This is because organising slides in squares, etc, is quite simple anyway, and the shapes can be made into paths. Usually in the software you will have to select the shape and tell your software to make it into a path. In Inkscape, transforming an object into a path will generally mean that the whole path is made of CubicBezier curves, which are unnecessarily complex. Using the "Simplify" command in Inkscape is usually enough to make the shapes into paths.

Shape-scaling

Hovercraft! will scale the path so that all the slides that need to fit into the path will fit into the path. If you therefore have several paths in your presentation, they will not keep their relative sizes, but will be resized so the slides fit. If you need to have the shapes keep their relative sizes, you need to combine them into one path.

Examples

To see how to use Hovercraft! in practice, there are three example presentations included with Hovercraft!

Take it easy

Don't go too heavy on the zoom. Having a difference between two slides in scale of more than 5 is rarely going to look good. It would make for a nice cool zooming effect if it did, but this is not what browsers are designed for, so it won't.

And the 3D effects can be really cool if used well. But not all the time, it gets tiring for the audience.

Try, if you can, to use the zoom and 3D effects when they make sense in the presentation. You can for example mention the main topics on one slide, and then zoom in on each topic when you discuss it in more detail. That way the effects help clarify the presentation, rather than distract from it.

Custom fonts

Browsers tend to render things subtly differently.

They also have different default fonts, and different operating systems have different implementations of the same fonts. So to make sure you have as much control over the design as possible, you should always include fonts with the presentation. A good source for free fonts are Google Webfonts. Those fonts are free and open source, so you can use them with no cost and no risk of being sued. They can also be downloaded or included online.

Online vs Downloaded

If you are making a presentation that is going to run on your computer at a conference or customer meeting, always download the fonts and have them as a part of the presentation. Put them in a folder called fonts under the folder where your presentation is.

You also need to define the font-family in your CSS. Font Squirrel's webfont generator will provide you with a platform-independent toolkit for generating both the varius font formats and the CSS.

If the presentation is online only, you can put an @include-statement in your CSS to include Googles webfonts directly:

@import url(http://fonts.googleapis.com/css?family=Libre+Baskerville|Racing+Sans+One|Satisfy);

But don't use this for things you need to show on your computer, as it requires you to have internet access.

Test with different browsers

If you are putting the presentation online, test it with a couple of major browsers, to make sure nothing breaks and that everything still looks good. Not only are there subtle differences in how things may get positioned, different browsers are also good at different things.

I've tested some browsers, all on Ubuntu, and it is likely that they behave differently on other operating systems, so you have to try for yourself.

Firefox

Firefox 18 is quite slow to use with impress.js, especially for 3D stuff, so it can have very jerky movements from slide to slide. It does keep text looking good no matter how much you zoom. On the other hand, it refuses to scale text infinitely, so if you scale too much characters will not grow larger, they will instead start moving around.

Firefox 19 is better, but for 3D stuff it's still a bit slow.

Chrome

Chrome 24 is fast, but will not redraw text in different sizes, but will instead create an image of them and rescale them, resulting in the previous slide having a fuzzy pixelated effect.

Epiphany

Epiphany 3.4.1 is comparable to Firefox 19, possibly a bit smoother, and the text looks good. But it has bugs in how it handles 3D data, and the location bar is visible in fullscreen mode, making it less suitable for any sort of presentation.

The template configuration file

The configuration file is normally called template.cfg, but if you have several configuration files in one template directory, you can specify which one to use by specifying the full path to the configuration file. However, if you just specify the template directory, template.cfg will be used.

Template files are in configparser format, which is an extended ini-style format. They are very simple, and have only one section, [hovercraft]. Any other sections will be ignored. Many of the parameters are lists that often do not fit on one line. In that case you can split the line up over several lines, but indenting the lines. The amount of indentation doesn't make any difference, except aesthetically.

The parameters in the [hovercraft] section are:

An example:

[hovercraft]
template = template.xsl
css = css/screen.css
css-print = css/print.css
js-header = js/dateinput.js
js-body = js/impress.js
          js/hovercraft.js
resources = images/back.png
            images/forward.png
            images/up.png
            images/down.png

The template file

The file specified with the template parameters is the actual XSLT template that will perform the translation from XML to HTML.

Most of the time you can just copy the default template file in hovercraft/templates/default/template.xsl and modify it. XSLT is very complex, but modifying the templates HTML is quite straightforward as long as you don't have to touch any of the <xsl:...> tags.

Also, the HTML that is generated is XHTML compatible and quite straightforward, so for the most case all you would need to generate another version of HTML, for example strict XHTML, would be to change the doctype.

But if you need to add or change the main generated HTML you can add and change HTML statements in this main file as you like. See for example how the little help-popup is added to the bottom of the HTML.

If you want to change the way the reStructuredText is rendered things get slightly more complex. The XSLT rules that convert the reStructuredText XML into HTML are contained in a separate file, reST.xsl. For the most part you can just include it in the template file with the following code:

<xsl:import href="resource:templates/reST.xsl" />

The resource: part here is not a part of XSLT, but a part of Hovercraft! It tells the XSLT translation that the file specified should not be looked up on the file system, but as a Python package resource. Currently the templates/reST.xsl file is the only XSLT resource import available.

If you need to change the way reStructuredText is rendered you need to make a copy of that file and modify it. You then need to make a copy of the main template and change the reference in it to your modified XSLT file.

None of the XSLT files need to be copied to the target, and should not be listed as a resource in the template configuration file.