Oliver Steele

Isn’t Scott Kim one of the people interviewed in Programmers at Work? Cool.

Mind giving a few details on how you implemented this?

Thanks! It’s an OpenLaszlo application; the core looks like this:

[code language="xml"]


width="${canvas.width}" height="${canvas.height}"
resource="oflip.swf" stretches="both"/>


x="${-canvas.width/2}" y="${-canvas.height/2}"
onclick="spin()">

[/code]

class defines a view that’s scaled to the canvas size and that embeds a Flash movie of the image. The three levels of view hierarchy are because ‘rotation’ is relative to the origin (the upper left corner); the x@ and @y on inner place the center of the image at the origin of the rotor, and the x@ and @y on outer place the origin of the rotor at the center of the canvas. With matrices you rotate around a point by sandwiching the rotation between a translation and its inverse; instead I represent each transformation as a view and let the rendering engine do this, so that I can animate the rotation attribute and let the animation system handle the rest.

To get the shadow, move the x@ and @y from inner to the definition of oflip in the code above, and then make two more copies of oflip right above rotor. An interval timer copies the rotations from inner -> s1@ -> @s2 on each frame.

[code language="xml"]

[/code]

Mouse tracking uses Math.atan2 and the mouse position relative to outer. Motion blur animates the blur effect’s blur radius up to 4 when the image is spinning and back down to 0 when it stops. Both of these piggy-back on the same interval timer that makes the shadow. I tried to turn off the effects when the frame rate got slow, but I don’t think this worked, and I ran out of time.