- Web Slideshows -

The World Wide Web is a great technology for hypertext, allowing users to collect documents from around the world with a single click, in any order they choose. But what if you, HTML author extraordinaire, want to create a sequential presentation (i.e. slideshow) for browsers?

The first idea that comes to mind is a link at the bottom of every page, leading to the next. But there's another way -- several other ways, actually. In this column we'll look at what you, as a CCN user or Information Provider, can use to give your Web pages slideshow-like effects.

Client Pull (full-page slideshows)

Client Pull works with Netscape 1.1 and above, as well as most other browsers. (Please note that it does not work with Lynx!) It allows you to specify, using HTML, that the user's Web browser should automatically load another Web page after a specified delay.

To do this, you need to put a special HTML tag in the <HEAD> section of your document, preferably as the first tag in that section. The tag looks like this:
<meta http-equiv="Refresh" content="4; URL=">

This tag instructs the Web browser to wait 4 seconds, and then load, which could then in turn contain another <META> tag instructing the browser to load another document. Using this technique you could put together an infinite loop -- that is, one document which leads to another which leads back to the first.

Replace the 4 in the above <META> tag with the desired delay, and replace with the URL of the next document. Note that this must be an absolute (full) URL: that is, you need to specify the full machine name and location. (More information on absolute vs. relative URLs can be found in IP Training 2.)

Remember to make your delay long enough so that the user can read the document. It's usually best to let the user know that the next page will be loaded automatically so that s/he is not surprised. Also, please put a link to the next document at the bottom, top, or both -- not all browsers support client-pull. If you create an infinite loop, please provide a link out -- going to another document is the only way for the user to stop the loop. If your browser supports client-pull, try this example. For more information on client-pull, read Netscape's information on dynamic documents.

GIF Animation (changing images)

If you simply want an animated image, with the rest of the document staying the same, then GIF animation should do the trick. GIF animation is a way of storing multiple frames of an animation in one GIF file, and is supported by newer browsers such as Netscape 2.0 and Microsoft Internet Explorer 2.0, to name a few.

Creating animated GIFs can, unfortunately, be tedious and complicated. This task is made easier by "wizards" which can be found in most GIF animation programs.

There are many such programs available. Some of these programs (such as GIF Construction Set) will also allow you to create transparent GIFs. Transparent GIFs are images with "see-through" parts which show the Web page's background color or image. This allows you to create an image of, say, a red circle, and make it look like the circle is "floating" on top of the Web page's background instead of an ugly rectangle. Transparent GIFs are supported by nearly all browsers.

Below is an incomplete list of GIF animators. For a larger selection, Quick Search the Virtual Software Library for your platform using the search terms "gif" and "animat". ("animat", not "animate")

Remember, not all browsers support animated GIFs. In most cases these older browsers will display just the first frame of the GIF -- so take that into account when designing your animation. Also, note that animated GIFs can be used just like normal GIFs -- as inline animated images with the <IMG> tag, and as animated links to other documents. I have seen this technique in use on several Web pages, and it looks very slick if used properly.

[Animated Tips for Power Users logo]

Java Animation (not recommended)

Java (Sun's new programming language for the Web) will probably have many practical uses, but animation is not one of them. Some sites use Java "applets" within their pages to display a series of images when an animated GIF would be smaller, faster, and supported by more browsers.


Chebucto Connections TIPS FOR POWER USERS
is edited by Michael Smith
who is happy to receive Questions, Comments or Suggestions.
If your browser does not support mail, write to Michael later at aa529@ccn·cs·dal·ca.

Last Month: May 1996