1、第 1 页 附录一英文原文 Animated conversation Developing decent web animations has been more like a climb up the Eiger than a walk in the park. However, the latest breed of software available has been built to capture the designers imagination without killing off the muse. Alistair Dabbs goes through the moti
2、ons. Lets face it, the Web is a disappointment. Its that tiny little screen, the narrow bandwidth and the uncertainty that vast numbers of your audience might not be able to see what you want them to. Everything to do with Web design is about downsizing. And if it wasnt bad enough having to make all
3、 your static graphics 72dpi, any attempt at animation involves considerable cramming effort. What this means, at least until large screens and fast Internet connections become the norm, is you cant yet do much with video. You can stream QuickTime, but without a leased line connection its terrible. T
4、hankfully, you still have a range of choices when it comes to graphics animation. So, lets take a look at the main techniques, and their drawbacks, for getting your site animated today. Back in 1994, the backroom boys in commercial Web development came up with an extremely basic form of animation by
5、 sending consecutive GIF images live to the browser. Advertisers had been using this method to change ad banners every 30 seconds or so without waiting for the user to refresh the page. By sending a sequence of frames on a constant basis, an elementary animation effect was possible. The drawback, of
6、 course, was that graphic data was constantly being downloaded over the line after the page itself had loaded. On a 14.4K modem, this meant the browser was always flickering and the hard disk churning, and frames were usually interspersed with blanks as each subsequent frame loaded. Soon after, the
7、animated GIF was born, effectively packing the GIF frame sequence into one file which downloaded once. The animated GIF has been a staple of ad banners and simple attention-grabbing effects ever since. Even sites which promote and showcase Flash and Shockwave interfaces still use animated GIFs becau
8、se designers know that its the one animation technology supported in every Web browser that lets you see graphics at all. The limitations of animated GIFs are well-known, but lets summarise them anyway. GIFs are bitmap images, so come at a fixed size regardless of browser window size. They can reach
9、 quite exciting sizes if they include more than 10 frames or so, because compression is based on the number of different colours in each image. They also tend to appear in a jerky fashion during the download, leaving the user staring at a seemingly inexplicable sequence running at one frame every fi
10、ve seconds the first time round. More recently, designers have been able to produce basic path motion for static images using DHTML. Instead of running an animation in one fixed place, DHTML techniques let you take a single image and move it around over the top of your page as an independent, floati
11、ng object. The nice thing about this approach is that the animation, for what it is, starts almost immediately and the movement is perfectly smooth, not being frame-based. The graphic can also have a transparent background just like any GIF. The big drawback is that it doesnt do anything else terrib
12、ly interesting. As a result it can come across as just plain annoying or tacky. And its not really animation. While the World Wide Web Consortium squandered most of the 1990s considering some proper animation technologies, Macromedia just went for it. The result was Flash, a system of playing back s
13、elf-contained movies containing vector-based graphics and text within a Web page or independently running in a Web browser. The advantages of the Flash approach are considerable, and getting more compelling as time goes on. In the first instance, the vector nature of Flash movies allows you to inclu
14、de quite complex graphics and sequences in the confidence that theyll compress down to almost unfeasibly small file sizes. In practically every test, from simple rollover type and button effects to complete sequences, youll find that Flash files are smaller than animated GIFs and load up faster than
15、 Java actions. Vectors also mean that the movies can resize themselves automatically to fit the browser screen, anti-aliasing on the fly. Better still, Flash movies can incorporate events and react to user input, making it terrific for developing custom Web page interfaces which HTML couldnt hope to
16、 imitate. Not least, Flash can include embedded audio. And perhaps best of all from an experienced designers point of view, the movies can be set to start running as soon as the download commences without waiting for it to complete. There are two principal drawbacks to the Flash format. First, it re
17、quires your audience to have a plug-in Flash player installed. However, to Macromedias credit, the Flash plug-in is a relatively small and speedy download at just a couple of hundred kilobytes. You should also be aware that Microsoft 3 intends dumping most of the plug-ins it currently ships with Int
18、ernet Explorer in future - but Flash is the very notable exception. The second drawback might not concern you, but its that Flash isnt actually a standard in the same way as HTML, GIF, JPG, PNG or something like Java. Flash is a 100 per cent proprietary format owned by Macromedia and licensed out to
19、 other graphics software developers on a commercial basis. In practice, of course, it doesnt matter that Flash isnt an officially recognised standard because well over 90 per cent of Internet users already have the plug-in installed: were talking about hundreds of millions of people, ready to go wit
20、h your animation content. Fun and sexy though Flash is, its not a complete multimedia environment. Originally, Flash arose from a project at Macromedia to make Shockwave animations, already developed for Web playback, even more compact and accessible by people with slow modems. Shockwave is still ve
21、ry much alive and well, and in many cases leaves Flash way behind in terms of visual quality, interactivity and multifunctionality. Theres even a lively market for cartoons and games using Shockwave and its offline player ShockMachine. Unlike Flash, however, the Shockwave plug-in is a long download
22、and requires a somewhat fiddly installation process which includes exiting your Web browser at one point. The big limitation of both Flash and Shockwave from a graphic artists point of view is that the really clever interactive features depend on scripting. Or to choose another word, programming. If
23、 youre happy about scripting, indeed if you have some JavaScript experience, youll find Flash is reasonably approachable； if not, youll be limited to more conventional animation tasks. Inevitably, everyone is always on the hunt for a Web animation system that doesnt expect the audience to locate and
24、 install third-party plug-ins. These exist, but they do so with solutions that are even more proprietary than Flash, and usually protected by their creators with ridiculously extreme caution. One example of an alternative to Flash that doesnt require a plug-in is CyberSpot. To all intents and purpos
25、es, a CyberSpot sequence looks a bit like a basic Flash movie with audio but it loads up in an instant without any preliminaries. The problem with it is that CyberSpot is marketed as a bespoke service by the company that developed it. You commission them to create a 30-second movie on your behalf, rather than create your own using standard software packages. As you can imagine, this is of limited use except as standalone ads. The hot technology everyone is talking about at the moment that could rival Flash at some point in the future is Scalable Vector Graphics, or SVG. It began
