The primary goal of many of the talks I’ve given is to duplicate a mental structure from my mind into the minds of my listeners so that they can understand it well enough to make their own judgments and possibly make use of the ideas. Or perhaps this is secondary to the goal of getting out of paying to attend the conference, but how better to continue doing that than to consistently help the audience to learn?
Often these mental structures are represented in my mind by visual or spatial relationships. In these cases my slide-based presentations tended to incorporate lots of diagrams so that my audience could see roughly how the ideas look to me. Often diagrams on different slides would duplicate substantial amounts of information from previously seen diagrams, in order to represent various things such as changes over time, added detail, or how a previous diagram fit into a more comprehensive idea.
But although there were real relationships between the diagrams on different slides, I felt slide-based presentation tools used effects in a way that obscured these relationships. For example, slides often move off to the left to reveal the next slide, suggesting to the audience that the previous diagram somehow belongs over there. Other effects such as fades, sliding vertically, flipping over, etc. are rarely any more helpful.
TractionSVG is my humble attempt to build something that allows me to illuminate rather than obscure these relationships. I can use it to show an audience an undetailed diagram, then zoom in to different parts and show more detail. Rather than duplicating parts of diagrams, I can add or change visual elements of a single diagram and therefore hopefully introduce less mental discontinuity in audience members.
You can take a look at how I used it at Clojure/conj 2011 here: https://chouser.us/conj-2011-cljs.svg
—Chouser, Dec 2011
Just point a supported browser at the presentation `.svg` file, and you should see the first step of the presentation. Speaker’s notes will pop up in a separate window, so you may need to disable your popup blocker if you want to see them.
To advance to the next step, do any of:
- Press space
- Press the right arrow
- Click on the right-hand half of the presentation window
- Click on the header for the next step in the speaker’s notes window
To zoom to the previous step, do any of:
- Press the left arrow
- Click on the left-hand half of the presentation window
- Click on the header for the previous step in the speaker’s notes window
You can also jump to any arbitrary step by clicking its header in the speaker’s notes window.
In Chrome on Linux you can press F11 to enter fullscreen mode. This is perfect for showing on a projector while keeping the speaker’s notes on your laptop screen.
TractionSVG has been tested most thoroughly on Chrome and Safari for iPhone, but has been reported to work on Safari and Firefox as well.
The browser loads the `.svg` file which contains a link to (or a copy of) the `traction.js` JavaScript file. This JavaScript finds the presentation config, either from inside the `.svg` or in a separate config file. It uses instructions in this config to adjust the SVG DOM in various minor ways, opens a speaker’s notes window, and begins playing the presentation.
The presentation’s `.svg` file may contain everything required for the presentation, including images, the config and the contents of `traction.js`. Used this way, an entire presentation can be single file called an “uber-traction”, usable directly from any supported browser. The file may minimally contain however just a link to `traction.js` and the SVG elements to be displayed.
A presentation’s config will refer to the XML `id` attributes of elements in the `.svg` file. Also, every SVG `rect` element whose XML `id` begins with `view-` will be hidden immediately when the browser loads the presentation. These view rects will be used to control pre-set areas the browser’s view can be zoomed to.
The config for a presentation is an XML fragment that may be put either inside the `.svg` file, which allows for building an uber-traction, or in separate file named `config.xml`.
The separate `config.xml` file must be in the same directory as the `.svg` file [note: the specifics of how the `config.xml` file is found are likely to change]. This is ideal for presentation development as it allows you to make and save changes to the `config.xml` and `.svg` files from different tools (such as a text editor and inkscape, respectively) at the same time. However, some browsers will not allow SVG at a `file:` URL to load the separate `config.xml` file, so you may need to run a local web server to make both the `.svg` and `config.xml` available to the browser during development.
If a `config.xml` file is found, it takes precedence over any config element that may be included in the `.svg`.
The JavaScript is of course the heart of the TractionSVG system, but should not require any customization from one presentation to another. It is generated by the ClojureScript compiler from sources in this repo’s `src` directory, but the resulting `tranction.js` is also checked in for convenient use without having to install or use the ClojureScript compiler. A presentation’s `.svg` file simply needs to refer to, or have a copy of, the `traction.js` file.
The recommended way to create a presentation is to use an SVG editor such as inkscape, an XML editor (vim or emacs works well), a lighttpd, and a supported web browser. Note that only a browser is needed for viewing a completed presentation.
Let’s say you want to create a presentation named ‘mypres’. Start in the directory that contains this README. Then:
$ cp -a example ~/mypres $ cd ~/mypres $ mv example.svg mypres.svg $ lighttpd -D -f lighttpd.conf
Now point your web browser to `http://localhost:8080/mypres.svg` and you should see a friendly welcome message. Edit the `config.xml` and `mypres.svg` files at will, and reload the page in the browser to see your changes.
SVG elements that are very small may not be rendered at all in some browsers, even when you zoom in. To compensate for this, the body of the graphic is very large – much larger than a 8.5x11 page.
View rectangles are in a separate inkscape layer, which makes them easy to hide interactively. They are also colored green to help them stand out from the background. TractionSVG ignores all this however, and only pays attention to the XML element ids. View rectangles are simply `rect` elements whose ids start with “view-“.
You can share your presentation directory if you’d like, which might work especially well if you host it on a web site somewhere. However, if you’d like to be able to email your presentation or otherwise send it around without a properly configured web server involved, it may be best to pull all of your files into a single uber-traction presentation file.
Currently this is a manual process, so you’ll need to open your `.svg` file in an XML or text editor. It’s a good idea to close your SVG editor before doing this so you don’t accidentally have it overwrite textual changes you’ll be making to the `.svg` file.
Simply paste the contents of your `config.xml` file into your `.svg` file. Immediately inside the opening `<svg>` tag is a file place to put it. Note that if TractionSVG can find a `config.xml` in the same directory as your `.svg` file, that will take precedence over what you just pasted, so you may want to build your uber-traction file in a new file in a separate directory or something.
Your `.svg` may now look something like this:
<svg …> <steps xmlns=”http://chouser.n01se.net/traction/config”> <init>…</init> <step>…</step> … </steps> <script xlink:href=”traction.js” type=”text/ecmascript”> <defs>…</defs> … </svg>
It may look different later if you load the `.svg` file in inkscape and save it back out. Inkscape may adjust where XML namespaces are declared and such, but this shouldn’t cause any problems for TractionSVG.
The snippet above shows the script tag that is used to load the TractionSVG JavaScript. To include the contents of the JavaScript instead of just having a reference to it, replace that script tag with one like this:
<script type=”text/ecmascript”><![CDATA[ … ]]> </script>
Then replace `…` with the contents of the `traction.js` file.
Here are some ideas to inspire you in your quest to find improvements you could contribute:
- Add a way to link from the `.svg` to a specific config file (rather than always using `config.xml` in the same directory)
- Add view transforms besides zoom, such as rotate.
- Add animation attributes besides opacity, such as position, rotation, etc.
- Provide a speakers-notes view within page (instead of only as popup) for more pleasant viewing by individuals later.
- Add in-browser presentation editor (start small – allow fixing of typos, then config tweaks, eventually allow editing of SVG and all supported features)
- Include an easy-to-start web server to support development (serving of config file, and eventually saving of changes made in the in-browser presentation editor)
