Katamari Hack

What is this?

This is a "bookmarklet" that turns any page into Katamari Damacy. Try clicking the Katamari! link above.

This was the winner of the 2011 Yahoo HackU contest at University of Washington.

How does it work?

Short version: css transforms (for things stuck to the katamari), canvas (drawing the katamari), and z-index (illusion of depth).

Long version: The bookmarklet loads kh.js into the current page.

Splits all the text on the page into words/spans. (StickyNodes::addWords)
Builds a grid data structure so that intersections with elements can be found quickly (StickyNodes::finalize). Essentially grid[floor(x / 100)][floor(y / 100)] is a list of elements in a 100x100 pixel block. This should probably be an R-tree, but the hot-spot in this program is definitely in the rendering.
The ball and stripes are drawn in a canvas that gets moved around the page (i.e. position: absolute; left: x; top: y;). See PlayerBall::drawBall.
When an element is attached to the katamari, a clone is made. The original element is hidden. The new element is moved around by setting -webkit-transform. The transform rotates the element about the rolling axis of the katamari and scales the element to make it look like it's coming out of the page. See PlayerBall::drawAttached, transform_test.html, and transform_test2.html.