by Charles Ying

Posts Tagged ‘Mobile’

Building CoverFlow for Safari on iPhone

Thursday, November 6th, 2008

Did you know that 3D graphics and animation is possible with Safari on iPhone?

If you have an iPhone, try out the CoverFlow (zflow) demo live with a live Flickr feed.

This CoverFlow demo is part of a new open source project I’ve started, CSS-VFX. The idea with CSS-VFX is to demonstrate all the cool things that are possible with Apple’s CSS Visual Effects extensions.

How does it work?

The zflow demo in CSS-VFX uses the Apple CSS Visual Effects extensions for hardware accelerated (on iPhone!) 3D perspective correct transforms and easily animated transitions. HTML 5 Canvas is used for simulating reflections.

  • zflow starts by loading each image from the images array. When each image is loaded, we scale the image to fit in a square region, and apply 3D CSS transforms to scale it in place.
  • Reflections – zflow then takes the scaled image and creates a Canvas element that contains a gradient alpha mask of the image’s reflection (using a “reflect” function to do this) and positions the canvas element in place.
  • Touch Controller – zflow creates a TouchController object, who’s job is to field touch events from Mobile Safari and calculate an appropriate offset.
  • Clicking – zflow detects when no move events have been made, and zooms + rotates the focused image forward by setting a “CSS Transition”ed 3D transform on the focused image. Clicking again transitions the image back.
  • Inertia – zflow achieves inertia by setting the “transition timing function” of the “tray” to an “ease-out” function, which slows things down. On the touch end event, we calculate the projected velocity and set the tray’s target position to that location. CSS Transitions handles the decay in velocity as the transition timing function executes — slowing the tray down gradually.

What’s next?

I hope that CSS-VFX can become a series of graphics gems that clearly illustrate how to use CSS Visual Effects, as well as talk about some of the corner cases and best practices to get the best performance. If you come up with something you’d like to include, please let me know. I’ll be tinkering with a few more gems myself, just watch the project for more as time goes on.

And tell a friend, I can’t wait to see what everyone else does with these great new features in Safari on iPhone.

Where to learn more

The CSS-VFX open source project is a good place to start. You can just use the zflow code in your own iPhone web pages (there’s docs on how to do that); and deep dive into the innerworkings of zflow to understand what exactly is going on.

Also, check out Apple’s proposed extensions: CSS 3D Transforms, CSS Transitions, and CSS Animation. They provide full specifications on what’s possible. Of course, there are a few gotchas when using these in practice, and I hope to document these as things progress.

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